ACS Publications. Most Trusted. Most Cited. Most Read
Quick View

OR SEARCH CITATIONS

My Activity
Publications
CONTENT TYPES

Figure 1Loading Img
Download Hi-Res ImageDownload to MS-PowerPointCite This:ACS Phys. Chem Au 2022, 2, 3, 191-198
RETURN TO ISSUEPREVArticleNEXT

First-Principles Calculation of Optoelectronic Properties in 2D Materials: The Polytypic WS2 Case

Cite this: ACS Phys. Chem Au 2022, 2, 3, 191–198
Publication Date (Web):January 10, 2022
https://doi.org/10.1021/acsphyschemau.1c00038

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY-NC-ND 4.0.
  • Open Access

Article Views

2647

Altmetric

-

Citations

5
LEARN ABOUT THESE METRICS
PDF (4 MB)
Get e-Alerts
Supporting Info (1)»
SUBJECTS:

Abstract

High Resolution Image
Download MS PowerPoint Slide

The phenomenon of polytypism, namely unconventional crystal phases displaying a mixture of stacking sequences, represents a powerful handle to design and engineer novel physical properties in two-dimensional (2D) materials. In this work, we characterize from first-principles the optoelectronic properties associated with the 2H/3R polytypism occurring in WS2 nanomaterials by means of density functional theory (DFT) calculations. We evaluate the band gap, optical response, and energy-loss function associated with 2H/3R WS2 nanomaterials and compare our predictions with experimental measurements of electron energy-loss spectroscopy (EELS) carried out in nanostructures exhibiting the same polytypism. Our results provide further input to the ongoing efforts toward the integration of polytypic 2D materials into functional devices.

This publication is licensed under

CC-BY-NC-ND 4.0.
  • cc licence
  • by licence
  • nc licence
  • nd licence
KEYWORDS:

Introduction

ARTICLE SECTIONS
Jump To
Two-dimensional (2D) materials of the transition metal dichalcogenide (TMD) family have attracted ample interest due to the wide range of tunability of their electronic and optical properties. (1−6) This flexibility in tailoring the physical properties of TMD materials can be traced back to their marked sensitivity with respect to the dimensionality, (7,8) specific edge configurations, (9−11) and stacking sequences. (12−15) The most common stacking sequences (polytypes) present in TMD materials are those based on the octahedral coordination (1T) and on the trigonal prismatic coordination (2H and 3R). (16−19) Furthermore, it has been reported that mixed 2H and 3R polytypes can also occur within the same TMD-based nanomaterial. This phenomenon, known as polytypism, leads to unconventional crystal phases displaying a mixture of stacking sequences and has been reported among several other TMD materials, including MoSe2, MoS2, and WS2. (20−22)
The different stacking sequences or polytypes exhibited by TMD nanostructures have associated specific variations in the resulting electronic and optical properties. For instance, 1T-MoS2 nanosheets are found to be metallic, (18) while their 2H and 3R counterparts display instead a semiconductor behavior. While extensive investigations of the optoeletronic properties of both the 2H and 3R polytypes in TMD materials have been carried out, much less is known about the implications of the 2H/3R mixed crystal phase. In this respect, achieving a deeper understanding of the optoelectronic properties associated with this 2H/3R polytypism is a key component of the ongoing efforts toward integrating polytypism-based TMD materials into functional devices.
Motivated by this, in this work we carry out first-principle calculations of the optoelectronic properties associated with the 2H/3R polytypism occurring in WS2 nanomaterials by means of density functional theory (DFT) (23,24) as implemented in the WIEN2k framework. We ascertain the semiconducting nature of 2H/3R polytypism and evaluate the corresponding band gap, the value of which is found to be in agreement with a recent experimental determination. (25) To obtain accurate estimates of the band gap and band structure associated with the different polytypes of WS2, we use the GW approximation as implemented in the GAP2 code by Jiang et al. (26,27) and that takes as input the output of the DFT calculations from WIEN2k. By combining DFT with GW calculations, we are able to evaluate the density of states (DOS), the band structure, the joint density of states (JDOS), and the energy-loss function (ELF) corresponding to 2H/3R WS2 nanomaterials. Furthermore, the calculations of the ELF can also be compared with the experimental measurements from electron energy-loss spectroscopy (EELS) carried out on WS2 nanostructures displaying the same 2H/3R polytypism.
Our analysis hence makes possible disentangling the dependence of the electronic and optical behavior of the 2H/3R mixed WS2 nanostructures on the underlying crystal structure. In turn, our results can be used to motivate further investigations of the growth mechanism of polytypes in 2D materials, and ultimately explore the possibilities in terms of achieving heterostructures based in a single TMD material.

Computational Techniques

ARTICLE SECTIONS
Jump To
The electronic properties of the 2H, 3R, and mixed 2H/3R polytypes of WS2 are investigated using both the linearized augmented plane wave (LAPW) and local orbitals (lo) methods as implemented in the WIEN2k Density Functional Theory package. (28) For the density of states (DOS) calculation, the van der Waals (vdW) interaction characteristic of WS2 polytypes is taken into account by implementing the nonlocal vdW functional model. (29,30) The nonlocal vdW interactions use optB88 (31) for the exchange term, the local density approximation (32) (LDA) for the correlation term, and the DRSLL kernel for the nonlocal term. (33) For the nonlocal vdW integration, the cutoff density rc is set to 0.3 bohr–3, while the plane wave expansion cutoff Gmax is set to 20 bohr–1. No spin polarization is considered.
The equilibrium lattice parameters for each of the three polytypes considered are found by volume and force optimization of the different unit cells, such that the force on each atom is less than 1.0 mRy/bohr. The total energy convergence criteria is set to be 0.1 mRy between self-consistent field (SCF) cycles, while the charge convergence criteria is set to 10–3e, with e being the elementary unit charge. The core and valence electron states were separated by an energy gap of −6.0 Ry. Furthermore, the calculations used a Rkmax value of 7.0, where R is the radius of the smallest Muffin Tin sphere and kmax is the largest k-vector.

Geometry Optimization

A geometrical optimization is carried out in order to find the equilibrium lattice parameter corresponding to the three 2H, 3R, and mixed 2H/3R WS2 polytypes. For each polytype, a specific amount of k-point sampling is employed until convergence is achieved with respect to the k-points, as indicated in Table 1. The k-points sampling of the first Brillouin zone for the lattice parameter calculations and all subsequent calculations using the DFT formalism are carried out using the tetrahedron method of Blöchl et al. (34)
Table 1. Values of the k-Mesh Used for the DFT Calculations and Crystal Structuresa
polytypek-meshcalculated lattice parameters
2H16 × 16 × 3a = b = 3.194 Å, c = 12.458 Å
3R14 × 14 × 14a = b = 3.199 Å, c = 18.733 Å
2H/3R24 × 24 × 3a = b = 3.205 Å, c = 19.057 Å
a

We also indicate, for each WS2 polytype, the calculated lattice parameters a, b, and c. For the 2H and 3R polytypes these values are consistent with the experimental values reported in the literature. (35).

The DFT calculations presented in this work are based on the structural atomic models displayed in Figure 1. Figure 1 schematics a and b display the atomic model of the 2H and 3R polytypes, respectively. The 2H polytype exhibits the characteristic hexagonal stacking order (AA′), where the adjacent layers are rotated 180° and stacked directly upon one another. The 3R polytype is characterized by the rhombohedral stacking order (BA), in which the adjacent layers are slightly displaced from each other without any rotation. Figure 1c shows the atomic model of the mixed 2H/3R WS2 polytypes, which is characterized by a layer stacking order of the type BAA′. This stacking order arises from the mixture of the 2H (AA′) and 3R (BA) polytypes. (36)

Figure 1

Figure 1. Schematic for the different polytypes of WS2. In the top panels, it is shown how all three polytypes exhibit a hexagonal structure when viewed from the [0001] direction; (a) the 2H crystal phase exhibits a honeycomb lattice, while the (b) 3R and (c) 2H/3R polytypes both have an atom in the middle of their honeycomb structures. The stacking sequences of the 2H, 3R, and their mixed 2H/3R polytypes can be better assessed when viewed from a lateral viewpoint with respect to the layers, as illustrated in the bottom panels.

High Resolution Image
Download MS PowerPoint Slide
The equilibrium lattice parameters obtained (see Figure S1 in the Supporting Information) for the three polytypes are shown in Table 1. The lattice parameters found for 2H and 3R are consistent with previously reported values in the literature. (35) For the mixed 2H/3R polytype, the lattice parameters are found to be a = b = 3.205 Å, and c = 19.057 Å. Furthermore, using the symmetry package available in WIEN2k, one can identify that the mixed 2H/3R phases belongs to the P3m1 space group.

GW Approximation

After geometry optimization, the equilibrium lattice parameters obtained are used for the calculations using the GW approximation as implemented in the GAP2 code. There, the Green’s function G and the screened Coulomb interaction W are calculated in the RPA framework. For the 2H and mixed 2H/3R crystal phases, we use a 6 × 6 × 1 k-mesh sampling of the Brillouin zone, while a 6 × 6 × 6 k-mesh sampling is used instead for the 3R crystal phase case. Fourier interpolation is used to interpolate a fine k-mesh from the sparse-mesh originally used in the GW calculations to obtain quasiparticle energies. (37) Spin–orbit coupling effects are taken into account in a perturbative one-shot manner. Table 2 displays the values of the k-mesh used for the GW calculation and for the calculation of the DOS, band structure, and ELF. These k-meshes are kept the same for the calculations with and without spin-orbit coupling.
Table 2. Values of the k-Mesh Used for the GW Calculation and for the Calculation of the DOS, Band Structure, and ELFa
crystal phaseGW calculationDOS, band structure, ELF
2H/3R6 × 6 × 123 × 23 × 3
2H6 × 6 × 120 × 20 × 4
3R4 × 4 × 416 × 16 × 16
a

These k-meshes are kept the same for the calculations with and without spin-orbit coupling.

Results and Discussion

ARTICLE SECTIONS
Jump To

Density of States and Band Structure

Figure 2 panels a and b display the total density of states (TDOS), the projected density of states (PDOS), and the electronic band structure corresponding to the mixed 2H/3R polytype, together with their counterparts for the 2H and 3R polytypes, Figure 2 panels c and d and panels e and f, respectively. The TDOS corresponding to the three polytypes are similar with and without SOC effects. By comparing the TDOS with the PDOS of the mixed 2H/3R, 2H, and 3R, one can observe how the W d-orbitals are the primarily allowed occupied and unoccupied states near the Fermi energy. This finding is consistent with related DFT studies based on the MoS2 bulk crystal structure. (2,38)

Figure 2

Figure 2. Left panels: the calculated density of states associated with the (a) 2H/3R, (c) 2H, and (e) 3R polytypes with and without spin–orbit coupling (SOC) taken into account. Right panels: the resulting band structures of the (b) 2H/3R, (d) 2H, and (f) 3R polytypes evaluated with and without SOC.

High Resolution Image
Download MS PowerPoint Slide
For the band structure calculations, the k-paths in the primitive Brillouin zones are chosen in a way such that the complete irreducible set of symmetry lines is obtained. In the case of 2H and mixed 2H/3R polytypes, identical k-paths (Γ → M → K → Γ → A → L →H → A) in the Brillouin zone are chosen since their primitive Brillouin zone have the same symmetry points, see Supporting Information Figure S2. Notice that for the 3R polytype we follow the prescriptions of refs (39−44) for the selection of the k-path in the primitive Brillouin zone, see also Supporting Information Figure S3.
The DOS and band structure of the 2H and 2H/3R polytypes (with and without SOC effects) reveal that the conduction band (CB) minima is found to be at the same point in the Brillouin zone, located between the K and Γ points. The valence band (VB) maximum for the 2H polytype happens at the Γ point, while for the mixed 2H/3R polytype it lies at the A point. In the band structure of the mixed 2H/3R polytypes, near the Fermi energy an extra band appears (Figure 2b) as compared to the two bands in the 2H case (Figure 2d). This extra band near the Fermi energy in the mixed 2H/3R polytype is the origin of the shift of the VB maximum from the Γ point to the A point. As a consequence of the extra band near the Fermi energy, an additional band can be found near the K point, leading to additional bands appearing when taking spin–orbit coupling into account (see Supporting Information Figure S4). Therefore, the mixed 2H/3R polytype in bulk form exhibits an indirect band gap like in the 2H bulk form. Concerning the band gap energy of the mixed 2H/3R polytype, our calculations indicate a value of 1.40 eV (1.48 eV) with (without) SOC effects. These values are about 5% higher than for the 2H polytype, where the calculated band gap energy is instead 1.34 eV with SOC and 1.39 eV without SOC.
In the case of the 3R crystal structure, the VB maximum lies at the Z point, while the CB minimum lies between the Γ and X points in the Brillouin zone. Furthermore, the band near the Fermi energy is split into two bands at the B, X, and Q points in the Brillouin zone when including spin–orbit coupling. The CB minimum lies between the Γ and X points and is pushed down in energy when including spin–orbit coupling, while the maximum of the VB is not modified significantly by the inclusion of the spin–orbit coupling. Therefore, the resulting band gap for the 3R polytype turns out to be 1.54 eV without SOC and 1.39 eV with SOC. Hence one observes that the SOC effects have a more significant effect for the 3R polytype as compared to the 2H and 2H/3R cases, and indeed in Figure 2e one can see how the band gap value markedly decreases once SOC is taken into account. This effect might originate from the one-shot postinclusion of spin–orbit coupling in the GW calculations.
The indirect band gap value of the mixed 2H/3R polytype is consistent with the experimental one reported in refs (22and25). Furthermore, such a value lies in between those of the 2H and 3R polytypes in the cases with and without spin–orbit coupling.

Energy-Loss Function

An improved understanding of the optical response of the unconventional mixed 2H/3R polytype can also be achieved by means of the calculation of the energy-loss function (ELF). With this motivation, we now compare the ELF calculated at the DFT and at the GW levels, with and without taking into account the spin–orbit coupling interaction effects.
Figure 3 panels a and b display the ELF calculated along the out-of-plane direction (c-axes), a configuration which matches that of the underlying experimental EELS measurements. In the low-loss region below 10 eV, the DFT calculations exhibit distinctive features at 7 and 10 eV, while the GW calculations exhibit a well-defined peak at around 8 eV. For the region with energy losses between 10 and 30 eV, the main feature for both the DFT with (without) SOC and the GW with (without) SOC calculations is a peak located at 20.9 eV (21.4 eV) and 21.1 eV (21.7 eV), which can be identified with the bulk plasmon of WS2. Interestingly, the bulk plasmon locations differ by no more than 0.25 eV for both the DFT and GW calculations with and without SOC effects. This result can be understood since all the band structures contribute to the bulk plasmon feature, therefore the effect of the GW calculation is less significant when compared to that of the low-loss region where the features depend more sensitively on bands near the Fermi energy.

Figure 3

Figure 3. (a,b) Out-of-plane energy-loss function of the mixed 2H/3R polytype calculated on the DFT and GW level with and without taking spin–orbit coupling into account. (c,d) Experimental EELS measurements acquired on a WS2 nanostructure characterized by the same 2H/3R polytypism. Note that the zero-loss peak (ZLP) has not been subtracted from the EELS data in the bottom left panel.

High Resolution Image
Download MS PowerPoint Slide
Figure 3 panels c and d display then experimental EELS measurements acquired on a WS2 nanostructure also characterized by the same 2H/3R polytypism (22) in the same energy-loss range that the corresponding theoretical calculations determined. Note that the zero-loss peak (ZLP) has not been subtracted from the EELS data in the bottom left panel. In these experimental measurements, one observes in the low-loss region two peaks located at 3.5 and 8 eV. The peak at 8 eV, which can be associated to the interlayer coupling, is consistent with the features of the GW calculation both including and excluding SOC effects. On the other hand, the feature at 3.5 eV is not visible in the calculated ELF, but the calculated DOS in Figure 2a indicates that this peak is associated to a electronic transition from the occupied d states to the unoccupied d states of W. The absence of the feature at 3.5 eV energy loss can be explained due to limitations of the GW approach. Indeed, GW accurately describes a single-particle process; however, for optical excitations the effect of interactions between holes and electrons needs to be taken into account. Properly describing electron–hole interactions could be achieved by solving the Bethe-Salpeter Equations (BSE). (45−47) Further details about the origin of these two observed peaks in the low-loss region can be found in the JDOS discussion below.
Concerning the properties of the bulk plasmon, it is found to be located at around 23 eV in both the experimental EELS measurements and in the DFT and GW calculations, though in the latter case it appears at somewhat smaller energies. The minor difference between the calculated and experimentally measured positions of the bulk plasmon peak of the mixed 2H/3R polytype can be attributed to the exclusion of local field effects and nonzero momentum transfer effects while calculating the dielectric response of the material, as implemented in the optic package. (48−50)

Joint Density of States

We consider now the results for the joint density of states (JDOS) calculated at the GW level with and without taking spin–orbit coupling effects. We also evaluate the contribution of separate bands to the joint density of states to elucidate which ones are important in specific energy losses regions. We note that in the cases including spin–orbit coupling, we double the amount of bands needed with respect to the case without spin–orbit coupling to properly describe the energy-loss spectra. To properly describe the bulk plasmon peaks appearing in the energy-loss regions in the range between 10 to 30 eV range, a larger amount of bands needs to be incorporated into the joint density of states calculation; this is consistent with the concept of plasmons arising as collective excitations of the electrons in the material.
If one starts with the calculation of the joint density of states by including one valence band (VB), the top valence band, and one conduction band, specifically the bottom conduction band (CB), no contributions are observed, see Figure 4. As then one includes more valence and conduction bands in addition to the top valence band and the bottom conduction band, we can clearly assess the contributions of the different bands with respect to the features observed in the low-loss region (see Figure 4a–d). In particular, one can reproduce the features at 3 and 3.5 eV when adding the contributions from a total of 20 VBs and CBs in the JDOS calculation. The feature at around 4 eV does not arise in the experimental EELS data, perhaps due to limitations in the energy resolution. In addition, features at 5 and 6 eV are also observed in the JDOS but not in the experimental EELS measurements.

Figure 4

Figure 4. Calculated joint density of states of the 2H/3R crystal structure with the GW framework without (a,b) and with (c,d) spin–orbit coupling effects taken into account. Here VB and CB stand for valence band and conduction band, respectively.

High Resolution Image
Download MS PowerPoint Slide
In the energy-loss region below 10 eV, we observe that the top 20 valence bands and lower 20 conduction bands can almost completely describe the energy-loss region for the 2H/3R mixed phase. To describe the energy-loss region for energy loss near the bulk plasmon, all the conduction and valence bands available are needed, consistent with the collective excitation behavior of bulk plasmons. Furthermore, as we proceed toward smaller energy losses we can see that a decreasing amount of valence and conduction bands are needed to explain the peaks in the corresponding energy region for all the polytypes.

Discussion

ARTICLE SECTIONS
Jump To
Our first-principles calculations for the value of the band gap and the location of the bulk plasmon peak for the 2H crystal structure of WS2 are found to be in good agreement with previous theoretical and experimental work. (51,52) Therefore, we are confident that we can reliably apply the same theoretical infrastructure to predict the electrical and optical properties of the corresponding 2H/3R polytype.
In the case of 2H/3R polytypism, the location of the bulk plasmon peak ascertained in WS2 nanostructures by means of EELS (22,25) is rather similar to that of the bulk plasmon peak in the 2H polytype, in agreement with the theoretical predictions in this work. Furthermore, here we have also calculated that the 2H/3R polytype should exhibit an indirect band gap with a value in the range between 1.40 and 1.48 eV. This prediction is in excellent agreement with the experimental result reported in refs (22and25) in which a band gap value of 1.6–0.2+0.3 eV was extracted after subtracting the EELS zero-loss peak from the EELS data using machine learning techniques.
Finally, in the case of the 3R polytype we have calculated an indirect band gap with a value in between 1.39 and 1.54 eV. The large discrepancy for the band gap calculations in the cases with and without taking into account the spin–orbit coupling effects could be related to an insufficiently dense k-mesh used in the GW calculation for the 3R polytype. For this crystal structure, we also calculate a bulk plasmon peak, the position of which is close to that of the 2H and 2H/3R polytypes. To the best of our knowledge, no experimental measurements of the position of the bulk plasmon peak, the band gap type, or the band gap value have been reported for the 3R polytype, and hence it is not possible to compare our predictions to experimental data.

Conclusions

ARTICLE SECTIONS
Jump To
In this work we have carried out ab initio calculations using Density Functional Theory and the GW approximation of the optoelectronic properties of the 2H, 3R, and 2H/3R polytypes of WS2. We have demonstrated how the band gap value of the 2H/3R polytypism lies between the band gap values of the 2H and 3R polytypes, where it is observed to be closer to the 2H band gap value compared to the 3R band gap value. Furthermore, this first-principle calculation is in good agreement with corresponding experimental determination from EELS measurements. Comparable band structures were found of the 2H and 2H/3R polytypes, where the top of the valence band of the 2H/3R polytypism lies at the A high symmetry point. We have shown that the bulk plasmon peaks of all the polytypes occurs at similar energy-loss values. For the energy-loss function, we have determined the contribution of the different valence and conduction bands to the energy-loss intensity for different energy-loss regions. Our results provide key input toward assessing the feasibility of TMD-based heterostructures composed of a single material with mixed crystalline phases.

Supporting Information

ARTICLE SECTIONS
Jump To

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsphyschemau.1c00038.

  • Figures illustrating geometrical optimization of the 2H/3R, 2H, and 3R structures; the primitive Brillouin zone of the 2H, 3R, and mixed 2H/3R crystalline phases of WS2; a magnified image of the band structure of the 2H and 2H/3R crystal phases near the Fermi energy; and additional details about the computational methods(PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

ARTICLE SECTIONS
Jump To
  • Corresponding Author
  • Authors
    • Louis Maduro - Kavli Institute of Nanoscience, Delft University of Technology, Delft, 2628CJ, The Netherlands
    • Sabrya E. van Heijst - Kavli Institute of Nanoscience, Delft University of Technology, Delft, 2628CJ, The Netherlands;  Orcidhttps://orcid.org/0000-0001-5436-4019
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

ARTICLE SECTIONS
Jump To

The authors would like to thank Hong Jiang for assistance with the use of the GAP code. S.C.-B. acknowledge financial support from ERC through the Starting Grant “TESLA” grant agreement No. 805021. L.M. acknowledges support from The Netherlands Organizational for Scientific Research (NWO) through the NanoFront program.

References

ARTICLE SECTIONS
Jump To

This article references 52 other publications.

  1. 1
    Manzeli, S.; Ovchinnikov, D.; Pasquier, D.; Yazyev, O. V.; Kis, A. 2D transition metal dichalcogenides. Nature Reviews Materials 2017, 2, 17033,  DOI: 10.1038/natrevmats.2017.33
    Google Scholar
    1
    2D transition metal dichalcogenides
    Manzeli, Sajedeh; Ovchinnikov, Dmitry; Pasquier, Diego; Yazyev, Oleg V.; Kis, Andras
    Nature Reviews Materials (2017), 2 (2), 17033CODEN: NRMADL; ISSN:2058-8437. (Nature Publishing Group)
    A review. Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of at.-scale thickness, direct bandgap, strong spin-orbit coupling and favorable electronic and mech. properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examd. and their properties are discussed, with particular attention to their charge d. wave, superconductive and topol. phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVWmtr%252FO&md5=83d0f2b1adaae4e8cf09dceb3597f2da
  2. 2
    Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M. Band structure tunability in MoS2 under interlayer compression: A DFT and GW study. Phys. Rev. B 2013, 87, 245114,  DOI: 10.1103/PhysRevB.87.245114
    Google Scholar
    2
    Band structure tunability in MoS2 under interlayer compression: a DFT and GW study
    Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M.
    Physical Review B: Condensed Matter and Materials Physics (2013), 87 (24), 245114/1-245114/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    The electronic band structures of MoS2 monolayer and 2H1 bulk polytype are studied within d.-functional theory (DFT) and many-body perturbation theory (GW approxn.). Interlayer van der Waals (vdW) interactions, responsible for bulk binding, are calcd. with the postprocessing Wannier functions method. From both fat bands and Wannier functions anal., it is shown that the transition from a direct band gap in the monolayer to an indirect band gap in bilayer or bulk systems is triggered by medium- to short-range electronic interactions between adjacent layers, which arise at the equil. interlayer distance detd. by the balance between vdW attraction and exchange repulsion. The semiconductor-to-semimetal (S-SM) transition is found from both theor. methods: around c = 10.7 Å and c = 9.9 Å for DFT and GW, resp. A metallic transition is also obsd. for the interlayer distance c = 9.7 Å. Dirac cone-like band structures and linear bands near Fermi level are found for shorter c lattice parameter values. The VdW correction to total energy was used to est. the pressure at which S-SM transition takes place from a fitting to a model equation of state.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1yms7fL&md5=89b3dd8bb0d22ea4720db63134fe9e30
  3. 3
    Johari, P.; Shenoy, V. B. Tunable Dielectric Properties of Transition Metal Dichalcogenides. ACS Nano 2011, 5, 5903– 5908,  DOI: 10.1021/nn201698t
    Google Scholar
    3
    Tunable Dielectric Properties of Transition Metal Dichalcogenides
    Johari, Priya; Shenoy, Vivek B.
    ACS Nano (2011), 5 (7), 5903-5908CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Since discovery of graphene, layered materials have drawn considerable attention because of their possible exfoliation into single and multilayer 2-dimensional sheets. Because of strong surface effects, the properties of these materials vary drastically with the no. of layers in a sheet. The authors have performed 1st-principles d. functional based calcns. to evaluate the electron energy loss spectrum (EELS) of bulk, monolayer, and bilayer configurations of several transition metal dichalcogenides, which include semiconducting as well as metallic compds. The authors' study shows that the peaks in the EELS spectra move toward larger wavelengths (red shift) with the decrease in no. of layers. The π plasmon peak shifts slightly by 0.5-1.0 eV, while a significant shift of ∼5.5-13.0 eV was obtained for π + σ plasmon, when exfoliated from bulk to single-layer. This underscores the importance of the interlayer coupling on the loss spectra and the dielec. properties. The authors' results are in very good agreement with the recent measurements performed by Coleman et al. (Science2011, 331, 568).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotlGis7o%253D&md5=5275a9e222e519449dd03407a299d2c2

    PMID: 21707067.

  4. 4
    Ramasubramaniam, A.; Naveh, D.; Towe, E. Tunable band gaps in bilayer transition-metal dichalcogenides. Phys. Rev. B 2011, 84, 205325,  DOI: 10.1103/PhysRevB.84.205325
    Google Scholar
    4
    Tunable band gaps in bilayer transition-metal dichalcogenides
    Ramasubramaniam, Ashwin; Naveh, Doron; Towe, Elias
    Physical Review B: Condensed Matter and Materials Physics (2011), 84 (20), 205325/1-205325/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    We investigate band-gap tuning in bilayer transition-metal dichalcogenides by external elec. fields applied perpendicular to the layers. Using d. functional theory, we show that the fundamental band gap of MoS2, MoSe2, MoTe2, and WS2 bilayer structures continuously decreases with increasing applied elec. fields, eventually rendering them metallic. We interpret our results in the light of the giant Stark effect and obtain a robust relationship, which is essentially characterized by the interlayer spacing, for the rate of change of band gap with applied external field. Our study expands the known space of layered materials with widely tunable band gaps beyond the classic example of bilayer graphene and suggests potential directions for fabrication of novel electronic and photonic devices.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFKltb3P&md5=9a2422ff4fdc0a84f03b2653f9ccd13a
  5. 5
    Gusakova, J.; Wang, X.; Shiau, L. L.; Krivosheeva, A.; Shaposhnikov, V.; Borisenko, V.; Gusakov, V.; Tay, B. K. Electronic Properties of Bulk and Monolayer TMDs: Theoretical Study Within DFT Framework (GVJ-2e Method). physica status solidi (a) 2017, 214, 1700218,  DOI: 10.1002/pssa.201700218
    Google Scholar
    There is no corresponding record for this reference.
  6. 6
    Ryou, J.; Kim, Y.-S.; Kc, S.; Cho, K. Monolayer MoS2 Bandgap Modulation by Dielectric Environments and Tunable Bandgap Transistors. Sci. Rep. 2016, 6, 29184,  DOI: 10.1038/srep29184
    Google Scholar
    6
    Monolayer MoS2 Bandgap Modulation by Dielectric Environments and Tunable Bandgap Transistors
    Ryou, Junga; Kim, Yong-Sung; Kc, Santosh; Cho, Kyeongjae
    Scientific Reports (2016), 6 (), 29184CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Semiconductors with a moderate bandgap have enabled modern electronic device technol., and the current scaling trends down to nanometer scale have introduced two-dimensional (2D) semiconductors. The bandgap of a semiconductor has been an intrinsic property independent of the environments and detd. fundamental semiconductor device characteristics. In contrast to bulk semiconductors, we demonstrate that an atomically thin two-dimensional semiconductor has a bandgap with strong dependence on dielec. environments. Specifically, monolayer MoS2 bandgap is shown to change from 2.8 eV to 1.9 eV by dielec. environment. Utilizing the bandgap modulation property, a tunable bandgap transistor, which can be in general made of a two-dimensional semiconductor, is proposed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFCrs7fP&md5=67cab9e695232edf801552072ea7b991
  7. 7
    Eknapakul, T.; King, P. D. C.; Asakawa, M.; Buaphet, P.; He, R.-H.; Mo, S.-K.; Takagi, H.; Shen, K. M.; Baumberger, F.; Sasagawa, T.; Jungthawan, S.; Meevasana, W. Electronic Structure of a Quasi-Freestanding MoS2 Monolayer. Nano Lett. 2014, 14, 1312– 1316,  DOI: 10.1021/nl4042824
    Google Scholar
    7
    Electronic Structure of a Quasi-Freestanding MoS2 Monolayer
    Eknapakul, T.; King, P. D. C.; Asakawa, M.; Buaphet, P.; He, R.-H.; Mo, S.-K.; Takagi, H.; Shen, K. M.; Baumberger, F.; Sasagawa, T.; Jungthawan, S.; Meevasana, W.
    Nano Letters (2014), 14 (3), 1312-1316CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Several transition-metal dichalcogenides exhibit a striking crossover from indirect to direct band gap semiconductors as they are thinned down to a single monolayer. Here, we demonstrate how an electronic structure characteristic of the isolated monolayer can be created at the surface of a bulk MoS2 crystal. This is achieved by intercalating potassium in the interlayer van der Waals gap, expanding its size while simultaneously doping electrons into the conduction band. Our angle-resolved photoemission measurements reveal resulting electron pockets centered at the K and K' points of the Brillouin zone, providing the first momentum-resolved measurements of how the conduction band dispersions evolve to yield an approx. direct band gap of ∼1.8 eV in quasi-freestanding monolayer MoS2. As well as validating previous theor. proposals, this establishes a novel methodol. for manipulating electronic structure in transition-metal dichalcogenides, opening a new route for the generation of large-area quasi-freestanding monolayers for future fundamental study and use in practical applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXivFWitLg%253D&md5=94b25a41d45dc2f7ad339bf7291e9603

    PMID: 24552197.

  8. 8
    Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105, 136805,  DOI: 10.1103/PhysRevLett.105.136805
    Google Scholar
    8
    Atomically Thin MoS2. A New Direct-Gap Semiconductor
    Mak, Kin Fai; Lee, Changgu; Hone, James; Shan, Jie; Heinz, Tony F.
    Physical Review Letters (2010), 105 (13), 136805/1-136805/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    The electronic properties of ultrathin crystals of MoS2 consisting of N = 1, 2,...,6 S-Mo-S monolayers were investigated by optical spectroscopy. Through characterization by absorption, photoluminescence, and photocond. spectroscopy, we trace the effect of quantum confinement on the material's electronic structure. With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by >0.6 eV. This leads to a crossover to a direct-gap material in the limit of the single monolayer. Unlike the bulk material, the MoS2 monolayer emits light strongly. The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 104 compared with the bulk material.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Chs7zL&md5=f29a2e9692fc341d1b921f7862cf4c2a
  9. 9
    Xu, H.; Liu, S.; Ding, Z.; Tan, S. J. R.; Yam, K. M.; Bao, Y.; Nai, C. T.; Ng, M.-F.; Lu, J.; Zhang, C.; Loh, K. P. Oscillating edge states in one-dimensional MoS2 nanowires. Nat. Commun. 2016, 7, 12904,  DOI: 10.1038/ncomms12904
    Google Scholar
    9
    Oscillating edge states in one-dimensional MoS2 nanowires
    Xu, Hai; Liu, Shuanglong; Ding, Zijing; Tan, Sherman J. R.; Yam, Kah Meng; Bao, Yang; Nai, Chang Tai; Ng, Man-Fai; Lu, Jiong; Zhang, Chun; Loh, Kian Ping
    Nature Communications (2016), 7 (), 12904CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Reducing the dimensionality of transition metal dichalcogenides to one dimension opens it to structural and electronic modulation related to charge d. wave and quantum correlation effects arising from edge states. The greater flexibility of a mol. scale nanowire allows a strain-imposing substrate to exert structural and electronic modulation on it, leading to an interplay between the curvature-induced influences and intrinsic ground-state topol. Herein, the templated growth of MoS2 nanowire arrays consisting of the smallest stoichiometric MoS2 building blocks is investigated using scanning tunnelling microscopy and non-contact at. force microscopy. Our results show that lattice strain imposed on a nanowire causes the energy of the edge states to oscillate periodically along its length in phase with the period of the substrate topog. modulation. This periodic oscillation vanishes when individual MoS2 nanowires join to form a wider nanoribbon, revealing that the strain-induced modulation depends on in-plane rigidity, which increases with system size.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1ejsb7O&md5=01c89de4a0a6a7106ae216dbe43416d0
  10. 10
    Tinoco, M.; Maduro, L.; Masaki, M.; Okunishi, E.; Conesa-Boj, S. Strain-Dependent Edge Structures in MoS2 Layers. Nano Lett. 2017, 17, 7021– 7026,  DOI: 10.1021/acs.nanolett.7b03627
    Google Scholar
    10
    Strain-Dependent Edge Structures in MoS2 Layers
    Tinoco, Miguel; Maduro, Luigi; Masaki, Mukai; Okunishi, Eiji; Conesa-Boj, Sonia
    Nano Letters (2017), 17 (11), 7021-7026CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Edge structures are low-dimensional defects unavoidable in layered materials of the transition metal dichalcogenides (TMD) family. Among the various types of such structures, the armchair (AC) and zigzag (ZZ) edge types are the most common. It has been predicted that the presence of intrinsic strain localized along these edges structures can have direct implications for the customization of their electronic properties. However, pinning down the relation between local structure and electronic properties at these edges is challenging. Here, we quantify the local strain field that arises at the edges of MoS2 flakes by combining aberration-cor. transmission electron microscopy (TEM) with the geometrical-phase anal. (GPA) method. We also provide further insight on the possible effects of such edge strain on the resulting electronic behavior by means of electron energy loss spectroscopy (EELS) measurements. Our results reveal that the two-dominant edge structures, ZZ and AC, induce the formation of different amts. of localized strain fields. We also show that by varying the free edge curvature from concave to convex, compressive strain turns into tensile strain. These results pave the way toward the customization of edge structures in MoS2, which can be used to engineer the properties of layered materials and thus contribute to the optimization of the next generation of at.-scale electronic devices built upon them.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslSit7%252FJ&md5=9079372f62c9db37ca8013b39e95dd86

    PMID: 29064254.

  11. 11
    Tinoco, M.; Maduro, L.; Conesa-Boj, S. Metallic edge states in zig-zag vertically-oriented MoS2 nanowalls. Sci. Rep. 2019, 9, 15602,  DOI: 10.1038/s41598-019-52119-3
    Google Scholar
    11
    Metallic edge states in zig-zag vertically-oriented MoS2 nanowalls
    Tinoco Miguel; Maduro Louis; Conesa-Boj Sonia; Tinoco Miguel
    Scientific reports (2019), 9 (1), 15602 ISSN:.
    The remarkable properties of layered materials such as MoS2 strongly depend on their dimensionality. Beyond manipulating their dimensions, it has been predicted that the electronic properties of MoS2 can also be tailored by carefully selecting the type of edge sites exposed. However, achieving full control over the type of exposed edge sites while simultaneously modifying the dimensionality of the nanostructures is highly challenging. Here we adopt a top-down approach based on focus ion beam in order to selectively pattern the exposed edge sites. This strategy allows us to select either the armchair (AC) or the zig-zag (ZZ) edges in the MoS2 nanostructures, as confirmed by high-resolution transmission electron microscopy measurements. The edge-type dependence of the local electronic properties in these MoS2 nanostructures is studied by means of electron energy-loss spectroscopy measurements. This way, we demonstrate that the ZZ-MoS2 nanostructures exhibit clear fingerprints of their predicted metallic character. Our results pave the way towards novel approaches for the design and fabrication of more complex nanostructures based on MoS2 and related layered materials for applications in fields such as electronics, optoelectronics, photovoltaics, and photocatalysts.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3MjjtFCksQ%253D%253D&md5=98b8e981314b20d7b00f8577346bfd8d
  12. 12
    He, J.; Hummer, K.; Franchini, C. Stacking effects on the electronic and optical properties of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. Phys. Rev. B 2014, 89, 075409,  DOI: 10.1103/PhysRevB.89.075409
    Google Scholar
    12
    Stacking effects on the electronic and optical properties of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2
    He, Jiangang; Hummer, Kerstin; Franchini, Cesare
    Physical Review B: Condensed Matter and Materials Physics (2014), 89 (7), 075409/1-075409/11CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    Employing the RPA we investigate the binding energy and Van der Waals (vdW) interlayer spacing between the two layers of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2 for five different stacking patterns, and examine the stacking-induced modifications on the electronic and optical/excitonic properties within the GW approxn. with a priori inclusion of spin-orbit coupling and by solving the two-particle Bethe-Salpeter equation. Our results show that for all cases, the most stable stacking order is the high symmetry AA' type, distinctive of the bulklike 2H symmetry, followed by the AB stacking fault, typical of the 3R polytypism, which is by only 5 meV/formula unit less stable. The conduction band min. is always located in the midpoint between K and Γ, regardless of the stacking and chem. compn. All MX2 undergo an direct-to-indirect optical gap transition going from the monolayer to the bilayer regime. The stacking and the characteristic vdW interlayer distance mainly influence the valence band splitting at K and its relative energy with respect to Γ, as well as, the electron-hole binding energy and the values of the optical excitations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlvFGmu7s%253D&md5=fc17f4973c3cc2f64745909f637ca006
  13. 13
    Suzuki, R.; Sakano, M.; Zhang, Y. J.; Akashi, R.; Morikawa, D.; Harasawa, A.; Yaji, K.; Kuroda, K.; Miyamoto, K.; Okuda, T.; Ishizaka, K.; Arita, R.; Iwasa, Y. Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry. Nat. Nanotechnol. 2014, 9, 611– 617,  DOI: 10.1038/nnano.2014.148
    Google Scholar
    13
    Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry
    Suzuki, R.; Sakano, M.; Zhang, Y. J.; Akashi, R.; Morikawa, D.; Harasawa, A.; Yaji, K.; Kuroda, K.; Miyamoto, K.; Okuda, T.; Ishizaka, K.; Arita, R.; Iwasa, Y.
    Nature Nanotechnology (2014), 9 (8), 611-617CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
    The valley degree of freedom of electrons is attracting growing interest as a carrier of information in various materials, including graphene, diamond and monolayer transition-metal dichalcogenides. The monolayer transition-metal dichalcogenides are semiconducting and are unique due to the coupling between the spin and valley degrees of freedom originating from the relativistic spin-orbit interaction. Here, we report the direct observation of valley-dependent out-of-plane spin polarization in an archetypal transition-metal dichalcogenide-MoS2-using spin- and angle-resolved photoemission spectroscopy. The result is in fair agreement with a first-principles theor. prediction. This was made possible by choosing a 3R polytype crystal, which has a non-centrosym. structure, rather than the conventional centrosym. 2H form. We also confirm robust valley polarization in the 3R form by means of circularly polarized photoluminescence spectroscopy. Non-centrosym. transition-metal dichalcogenide crystals may provide a firm basis for the development of magnetic and elec. manipulation of spin/valley degrees of freedom.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1ait77K&md5=357d1a1ca0cc8ab246da538f40dbc5b3
  14. 14
    Chen, L.; Feng, H.; Zhang, R.; Wang, S.; Zhang, X.; Wei, Z.; Zhu, Y.; Gu, M.; Zhao, C. Phase-Controlled Synthesis of 2H/3R-MoSe2 Nanosheets on P-Doped Carbon for Synergistic Hydrogen Evolution. ACS Applied Nano Materials 2020, 3, 6516– 6523,  DOI: 10.1021/acsanm.0c00988
    Google Scholar
    14
    Phase-Controlled Synthesis of 2H/3R-MoSe2 Nanosheets on P-Doped Carbon for Synergistic Hydrogen Evolution
    Chen, Lunfeng; Feng, Hanghang; Zhang, Rui; Wang, Suhang; Zhang, Xueyan; Wei, Zhijie; Zhu, Yuanmin; Gu, Meng; Zhao, Chenyang
    ACS Applied Nano Materials (2020), 3 (7), 6516-6523CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
    The nanoscale structure of catalysts has a profound influence on their physicochem. properties. However, the controlled synthesis of desired highly active microstructures is still challenging. In this work, through the introduction of phytic acid (PA), MoSe2 nanosheets with 2H/3R heterophases are successfully synthesized on a P-doped carbon substrate. Plenty of defects are introduced into the basal plane of MoSe2 with largely expanded interlayer spacings, which increase the no. of active sites and enhance the electronic/ionic transport and mass transfer. Benefiting from these structure merits, the obtained heterostructure exhibits superior HER activity and durability. A low overpotential of 164 mV is obsd. at a c.d. of 10 mA cm-2 with a Tafel slope of 44 mV dec-1. The HER performance is well maintained even after 10 h tests, showing superior electrochem. robustness. This controlled synthesis 2H/3R heterophased MoSe2 can be extended to other transitional metal chalcogenides (TMDs) for diverse applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1yntbbO&md5=b97ce510f6cd3f5a0ade38b1c1a7b0ed
  15. 15
    Wilson, J.; Yoffe, A. The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties. Adv. Phys. 1969, 18, 193– 335,  DOI: 10.1080/00018736900101307
    Google Scholar
    15
    Transition metal dichalcogenides. Discussion and interpretation of the observed optical, electrical, and structural properties
    Wilson, John Anthony; Yoffe, Abraham D.
    Advances in Physics (1969), 18 (73), 193-335CODEN: ADPHAH; ISSN:0001-8732.
    The transition metal dichalcogenides are ∼60 in no. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to <1000 Å and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of elec. and structural data available to yield useful working band models that are in accord with a MO approach. Several special topics have arisen: these include excition screening, d-band-formation, the metal/insulator transition, magnetism, and supercond. in such compds. High-pressure work seems to offer a possibility for testing the recent theory of excitonic insulators.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXjs1Ogug%253D%253D&md5=727600599d9dd61a97a338cafb741394
  16. 16
    Lukowski, M. A.; Daniel, A. S.; Meng, F.; Forticaux, A.; Li, L.; Jin, S. Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets. J. Am. Chem. Soc. 2013, 135, 10274– 10277,  DOI: 10.1021/ja404523s
    Google Scholar
    16
    Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets
    Lukowski, Mark A.; Daniel, Andrew S.; Meng, Fei; Forticaux, Audrey; Li, Linsen; Jin, Song
    Journal of the American Chemical Society (2013), 135 (28), 10274-10277CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Promising catalytic activity from MoS2 in the H evolution reaction (HER) is attributed to active sites located along the edges of its 2-dimensional layered crystal structure, but its performance is limited by the d. and reactivity of active sites, poor elec. transport, and inefficient elec. contact to the catalyst. Here the authors report enhanced HER catalysis (an electrocatalytic c.d. of 10 mA/cm2 at a low overpotential of -187 mV vs. RHE and a Tafel slope of 43 mV/decade) from metallic nanosheets of 1T-MoS2 chem. exfoliated via Li intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Structural characterization and electrochem. studies confirmed that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics and low-loss elec. transport and possess a proliferated d. of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make these metallic nanosheets a highly competitive earth-abundant HER catalyst.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpvFagtbs%253D&md5=6757bf06d9618bc12361b7a72c4d468a
  17. 17
    Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 2013, 13, 6222– 6227,  DOI: 10.1021/nl403661s
    Google Scholar
    17
    Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction
    Voiry, Damien; Salehi, Maryam; Silva, Rafael; Fujita, Takeshi; Chen, Mingwei; Asefa, Tewodros; Shenoy, Vivek B.; Eda, Goki; Chhowalla, Manish
    Nano Letters (2013), 13 (12), 6222-6227CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The authors report chem. exfoliated MoS2 nanosheets with a high concn. of metallic 1T phase using a solvent free intercalation method. After removing the excess of neg. charges from the surface of the nanosheets, highly conducting 1T phase MoS2 nanosheets exhibit excellent catalytic activity toward the evolution of H with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS2, the activity of 2H MoS2 decreased, consistent with edge oxidn. However, 1T MoS2 remains unaffected after oxidn., suggesting that edges of the nanosheets are not the main active sites. The importance of elec. cond. of the 2 phases on the H evolution reaction activity was further confirmed by using C nanotubes to increase the cond. of 2H MoS2.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsl2nsLnN&md5=972adb681c83a77d8d04bd7315d38a92
  18. 18
    Acerce, M.; Voiry, D.; Chhowalla, M. Metallic 1T phase MoS2 nanosheets as supercapacitor electrode materials. Nat. Nanotechnol. 2015, 10, 313– 318,  DOI: 10.1038/nnano.2015.40
    Google Scholar
    18
    Metallic 1T phase MoS2 nanosheets as supercapacitor electrode materials
    Acerce, Muharrem; Voiry, Damien; Chhowalla, Manish
    Nature Nanotechnology (2015), 10 (4), 313-318CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
    Efficient intercalation of ions in layered materials forms the basis of electrochem. energy storage devices such as batteries and capacitors. Recent research has focused on the exfoliation of layered materials and then restacking the two-dimensional exfoliated nanosheets to form electrodes with enhanced electrochem. response. Here, it is shown that chem. exfoliated nanosheets of MoS2 contg. a high concn. of the metallic 1T phase can electrochem. intercalate ions such as H+, Li+, Na+, and K+ with extraordinary efficiency and achieve capacitance values ranging from ∼400 to ∼700 F cm-3 in a variety of aq. electrolytes. It is also demonstrated that this material is suitable for high-voltage (3.5 V) operation in non-aq. org. electrolytes, showing prime volumetric energy and power d. values, coulombic efficiencies in excess of 95%, and stability over 5,000 cycles. As it is shown by X-ray diffraction anal., these favorable electrochem. properties of 1T MoS2 layers are mainly a result of their hydrophilicity and high elec. cond., as well as the ability of the exfoliated layers to dynamically expand and intercalate the various ions.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlt1aisr4%253D&md5=11ea2a3283936339127471a687184ca5
  19. 19
    Voiry, D.; Mohite, A.; Chhowalla, M. Phase engineering of transition metal dichalcogenides. Chem. Soc. Rev. 2015, 44, 2702– 2712,  DOI: 10.1039/C5CS00151J
    Google Scholar
    19
    Phase engineering of transition metal dichalcogenides
    Voiry, Damien; Mohite, Aditya; Chhowalla, Manish
    Chemical Society Reviews (2015), 44 (9), 2702-2712CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    Transition metal dichalcogenides (TMDs) represent a family of materials with versatile electronic, optical, and chem. properties. Most TMD bulk crystals are van der Waals solids with strong bonding within the plane but weak interlayer bonding. The individual layers can be readily isolated. Single layer TMDs possess intriguing properties that are ideal for both fundamental and technol. relevant research studies. We review the structure and phases of single and few layered TMDs. We also describe recent progress in phase engineering in TMDs. The ability to tune the chem. by choosing a unique combination of transition metals and chalcogen atoms along with controlling their properties by phase engineering allows new functionalities to be realized with TMDs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmslGjtbo%253D&md5=3b535ac3387c345182c704fbfaad8d79
  20. 20
    Puretzky, A. A.; Liang, L.; Li, X.; Xiao, K.; Wang, K.; Mahjouri-Samani, M.; Basile, L.; Idrobo, J. C.; Sumpter, B. G.; Meunier, V.; Geohegan, D. B. Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations. ACS Nano 2015, 9, 6333– 6342,  DOI: 10.1021/acsnano.5b01884
    Google Scholar
    20
    Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations
    Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; Xiao, Kai; Wang, Kai; Mahjouri-Samani, Masoud; Basile, Leonardo; Idrobo, Juan Carlos; Sumpter, Bobby G.; Meunier, Vincent; Geohegan, David B.
    ACS Nano (2015), 9 (6), 6333-6342CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The tunable optoelectronic properties of stacked 2-dimensional (2D) crystal monolayers are detd. by their stacking orientation, order, and at. registry. Atomic-resoln. Z-contrast scanning TEM (AR-Z-STEM) and EELS can be used to det. the exact at. registration between different layers, in few-layer 2D stacks; however, fast optical characterization techniques are essential for rapid development of the field. Using 2- and 3-layer MoSe2 and WSe2 crystals synthesized by CVD, the generally unexplored low frequency (LF) Raman modes (<50 cm-1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the no. of layers, but also their stacking configurations. Ab initio calcns. and group theory anal. corroborate the exptl. assignments detd. by AR-Z-STEM, and the calcd. LF mode fingerprints are related to the 2D crystal symmetries.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXot1eht74%253D&md5=d49e4c1c87ebd0a4cca5f537de3204ad

    PMID: 25965878.

  21. 21
    Lee, J.-U.; Kim, K.; Han, S.; Ryu, G. H.; Lee, Z.; Cheong, H. Raman Signatures of Polytypism in Molybdenum Disulfide. ACS Nano 2016, 10, 1948– 1953,  DOI: 10.1021/acsnano.5b05831
    Google Scholar
    21
    Raman Signatures of Polytypism in Molybdenum Disulfide
    Lee, Jae-Ung; Kim, Kangwon; Han, Songhee; Ryu, Gyeong Hee; Lee, Zonghoon; Cheong, Hyeonsik
    ACS Nano (2016), 10 (2), 1948-1953CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Since the stacking order sensitively affects various phys. properties of layered materials, accurate detn. of the stacking order is important for studying the basic properties of these materials as well as for device applications. Because 2H-molybdenum disulfide (MoS2) is most common in nature, most studies so far have focused on 2H-MoS2. However, we found that the 2H, 3R, and mixed stacking sequences exist in few-layer MoS2 exfoliated from natural molybdenite crystals. The crystal structures are confirmed by HR-TEM measurements. The Raman signatures of different polytypes are investigated by using three different excitation energies that are nonresonant and resonant with A and C excitons, resp. The low-frequency breathing and shear modes show distinct differences for each polytype, whereas the high-frequency intralayer modes show little difference. For resonant excitations at 1.96 and 2.81 eV, distinct features are obsd. that enable detn. of the stacking order.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvFKqtA%253D%253D&md5=a2a594c067a4ad57ebb33228109ab5a4

    PMID: 26756836.

  22. 22
    van Heijst, S. E.; Mukai, M.; Okunishi, E.; Hashiguchi, H.; Roest, L. I.; Maduro, L.; Rojo, J.; Conesa-Boj, S. Illuminating the Electronic Properties of WS2 Polytypism with Electron Microscopy. Ann. Phys. 2021, 533, 2000499,  DOI: 10.1002/andp.202000499
    Google Scholar
    22
    Illuminating the Electronic Properties of WS2 Polytypism with Electron Microscopy
    van Heijst, Sabrya E.; Mukai, Masaki; Okunishi, Eiji; Hashiguchi, Hiroki; Roest, Laurien I.; Maduro, Louis; Rojo, Juan; Conesa-Boj, Sonia
    Annalen der Physik (Berlin, Germany) (2021), 533 (3), 2000499CODEN: ANPYA2; ISSN:0003-3804. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Tailoring the specific stacking sequence (polytypes) of layered materials represents a powerful strategy to identify and design novel phys. properties. While nanostructures built upon transition-metal dichalcogenides (TMDs) with either the 2H or 3R cryst. phases have been routinely studied, knowledge of TMD nanomaterials based on mixed 2H/3R polytypes is far more limited. In this work, mixed 2H/3R free-standing WS2 nanostructures displaying a flower-like configuration are fingerprinted by means of state-of-the-art transmission electron microscopy. Their rich variety of shape-morphol. configurations is correlated with relevant local electronic properties such as edge, surface, and bulk plasmons. Machine learning is deployed to establish that the 2H/3R polytype displays an indirect band gap of EBG=1.6-0.2+0.3eV. Further, high resoln. electron energy-loss spectroscopy reveals energy-gain peaks exhibiting a gain-to-loss ratio greater than unity, a property that can be exploited for cooling strategies of atomically-thin TMD nanostructures and devices built upon them. The findings of this work represent a stepping stone towards an improved understanding of TMD nanomaterials based on mixed cryst. phases.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXmtFGks7c%253D&md5=8595a00a11525c8b3934e62d9b07ee6a
  23. 23
    Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, B864– B871,  DOI: 10.1103/PhysRev.136.B864
    Google Scholar
    There is no corresponding record for this reference.
  24. 24
    Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133– A1138,  DOI: 10.1103/PhysRev.140.A1133
    Google Scholar
    There is no corresponding record for this reference.
  25. 25
    Roest, L. I.; van Heijst, S. E.; Maduro, L.; Rojo, J.; Conesa-Boj, S. Charting the low-loss region in electron energy loss spectroscopy with machine learning. Ultramicroscopy 2021, 222, 113202,  DOI: 10.1016/j.ultramic.2021.113202
    Google Scholar
    25
    Charting the low-loss region in electron energy loss spectroscopy with machine learning
    Roest, Laurien I.; van Heijst, Sabrya E.; Maduro, Louis; Rojo, Juan; Conesa-Boj, Sonia
    Ultramicroscopy (2021), 222 (), 113202CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)
    A review. Exploiting the information provided by electron energy-loss spectroscopy (EELS) requires reliable access to the low-loss region where the zero-loss peak (ZLP) often overwhelms the contributions assocd. to inelastic scatterings off the specimen. Here we deploy machine learning techniques developed in particle physics to realize a model-independent, multidimensional detn. of the ZLP with a faithful uncertainty est. This novel method is then applied to subtract the ZLP for EEL spectra acquired in flower-like WS2 nanostructures characterised by a 2H/3R mixed polytypism. From the resulting subtracted spectra we det. the nature and value of the bandgap of polytypic WS2, finding EBG = 1.6+0.3-0.2eV with a clear preference for an indirect bandgap. Further, we demonstrate how this method enables us to robustly identify excitonic transitions down to very small energy losses. Our approach has been implemented and made available in an open source YTHON package dubbed EELSfitter.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtlWgtr4%253D&md5=41d5503df893b94b57887789d4042230
  26. 26
    Jiang, H.; Gómez-Abal, R. I.; Li, X. Z.; Meisenbichler, C.; Ambrosch-Draxl, C.; Scheffler, M. FHI-gap: A GW code based on the all-electron augmented plane wave method. Comput. Phys. Commun. 2013, 184, 348– 366,  DOI: 10.1016/j.cpc.2012.09.018
    Google Scholar
    26
    FHI-gap: A GW code based on the all-electron augmented plane wave method
    Jiang, Hong; Gomez-Abal, Ricardo I.; Li, Xin-Zheng; Meisenbichler, Christian; Ambrosch-Draxl, Claudia; Scheffler, Matthias
    Computer Physics Communications (2013), 184 (2), 348-366CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
    The GW method has become the state-of-the-art approach for the first-principles description of the electronic quasi-particle band structure in cryst. solids. Most of the existing codes rely on pseudopotentials in which only valence electrons are treated explicitly. The pseudopotential method can be problematic for systems with localized d- or \\f\\-electrons, even for ground-state d.-functional theory (DFT) calcns. The situation can become more severe in \\GW\\ calcns., because pseudo-wavefunctions are used in the computation of the self-energy and the core-valence interaction is approximated at the DFT level. In this work, we present the package FHI-gap, an all-electron \\GW\\ implementation based on the full-potential linearized augmented planewave plus local orbital (LAPW) method. The FHI-gap code can handle core, semicore, and valence states on the same footing, which allows for a correct treatment of core-valence interaction. Moreover, it does not rely on any pseudopotential or frozen-core approxn. It is, therefore, able to handle a wide range of materials, irresp. of their compn. Test calcns. demonstrate the convergence behavior of the results with respect to various cut-off parameters. These include the size of the basis set that is used to expand the products of Kohn-Sham wavefunctions, the no. of \\k\\ points for the Brillouin zone integration, the no. of frequency points for the integration over the imaginary axis, and the no. of unoccupied states. At present, FHI-gap is linked to the WIEN2k code, and an implementation into the exciting code is in progress.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVCisb7L&md5=dfcaffb5622570a5985f7495c1d99ccc
  27. 27
    Jiang, H.; Blaha, P. GW with linearized augmented plane waves extended by high-energy local orbitals. Phys. Rev. B 2016, 93, 115203,  DOI: 10.1103/PhysRevB.93.115203
    Google Scholar
    27
    GW with linearized augmented plane waves extended by high-energy local orbitals
    Jiang, Hong; Blaha, Peter
    Physical Review B (2016), 93 (11), 115203/1-115203/11CODEN: PRBHB7; ISSN:2469-9950. (American Physical Society)
    Many-body perturbation theory in the GW approxn. is currently the most accurate and robust first- principles approach to det. the electronic band structure of weakly correlated insulating materials without any empirical input. Recent GW results for ZnO with more careful investigation of the convergence with respect to the no. of unoccupied states have led to heated debates regarding the numerical accuracy of previously reported GW results using either pseudopotential plane waves or all-electron linearized augmented plane waves (LAPWs). The latter has been arguably regarded as the most accurate scheme for electronic-structure theory for solids. This work aims to solve the ZnO puzzle via a systematic investigation of the effects of including high-energy local orbitals (HLOs) in the LAPW-based GW calcns. of semiconductors. Using ZnO as the prototypical example, it is shown that the inclusion of HLOs has two main effects: it improves the description of high-lying unoccupied states by reducing the linearization errors of the std. LAPW basis, and in addn. it provides an efficient way to achieve the completeness in the summation of states in GW calcns. By investigating the convergence of GW band gaps with respect to the no. of HLOs for several other typical examples, it was found that the effects of HLOs are highly system-dependent, and in most cases the inclusion of HLOs changes the band gap by less than 0.2 eV. Compared to its effects on the band gap, the consideration of HLOs has even stronger effects on the GW correction to the valence-band max., which is of great significance for the GW prediction of the ionization potentials of semiconductors. By considering an extended set of semiconductors with relatively well- established exptl. band gaps, it was found that in general using a HLO-enhanced LAPW basis significantly improves the agreement with expt. for both the band gap and the ionization potential, and overall the partially self-consistent GW0 approach based on the generalized gradient approxn. gives an optimal performance.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVShurnL&md5=56567295648e472ec2524e32ab908e8b
  28. 28
    Blaha, P.; Schwarz, K.; Tran, F.; Laskowski, R.; Madsen, G. K. H.; Marks, L. D. WIEN2k: An APW+lo program for calculating the properties of solids. J. Chem. Phys. 2020, 152, 074101,  DOI: 10.1063/1.5143061
    Google Scholar
    28
    WIEN2k: An APW+lo program for calculating the properties of solids
    Blaha, Peter; Schwarz, Karlheinz; Tran, Fabien; Laskowski, Robert; Madsen, Georg K. H.; Marks, Laurence D.
    Journal of Chemical Physics (2020), 152 (7), 074101CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The WIEN2k program is based on the APW plus local orbitals (APW + lo) method to solve the Kohn-Sham equations of d. functional theory. The APW + lo method, which considers all electrons (core and valence) self-consistently in a full-potential treatment, is implemented very efficiently in WIEN2k, since various types of parallelization are available and many optimized numerical libraries can be used. Many properties can be calcd., ranging from the basic ones, such as the electronic band structure or the optimized at. structure, to more specialized ones such as the NMR shielding tensor or the elec. polarization. After a brief presentation of the APW + lo method, we review the usage, capabilities, and features of WIEN2k (version 19) in detail. The various options, properties, and available approxns. for the exchange-correlation functional, as well as the external libraries or programs that can be used with WIEN2k, are mentioned. Refs. to relevant applications and some examples are also given. (c) 2020 American Institute of Physics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjs1Kksbs%253D&md5=23465e0a29a40cfa996278efa98c642b
  29. 29
    Klimeš, J.; Bowler, D. R.; Michaelides, A. Chemical accuracy for the van der Waals density functional. J. Phys.: Condens. Matter 2010, 22, 022201,  DOI: 10.1088/0953-8984/22/2/022201
    Google Scholar
    29
    Chemical accuracy for the van der Waals density functional
    Klimes, Jiri; Bowler, David R.; Michaelides, Angelos
    Journal of Physics: Condensed Matter (2010), 22 (2), 022201/1-022201/5CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
    The non-local van der Waals d. functional (vdW-DF) of Dion et al is a very promising scheme for the efficient treatment of dispersion bonded systems. We show here that the accuracy of vdW-DF can be dramatically improved both for dispersion and hydrogen bonded complexes through the judicious selection of its underlying exchange functional. New and published exchange functionals are identified that deliver much better than chem. accuracy from vdW-DF for the S22 benchmark set of weakly interacting dimers and for water clusters. Improved performance for the adsorption of water on salt is also obtained.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFKitb8%253D&md5=37cca57a611ebd2fea99edd70d979091
  30. 30
    Klimeš, J. c. v.; Bowler, D. R.; Michaelides, A. Van der Waals density functionals applied to solids. Phys. Rev. B 2011, 83, 195131,  DOI: 10.1103/PhysRevB.83.195131
    Google Scholar
    30
    Van der Waals density functionals applied to solids
    Klimes, Jiri; Bowler, David R.; Michaelides, Angelos
    Physical Review B: Condensed Matter and Materials Physics (2011), 83 (19), 195131/1-195131/13CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    The van der Waals d. functional (vdW-DF) of M. Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] is a promising approach for including dispersion in approx. d. functional theory exchange-correlation functionals. Indeed, an improved description of systems held by dispersion forces has been demonstrated in the literature. However, despite many applications, std. general tests on a broad range of materials including traditional "hard" matter such as metals, ionic compds., and insulators are lacking. Such tests are important not least because many of the applications of the vdW-DF method focus on the adsorption of atoms and mols. on the surfaces of solids. Here we calc. the lattice consts., bulk moduli, and atomization energies for a range of solids using the original vdW-DF and several of its offspring. We find that the original vdW-DF overestimates lattice consts. in a similar manner to how it overestimates binding distances for gas-phase dimers. However, some of the modified vdW functionals lead to av. errors which are similar to those of PBE or better. Likewise, atomization energies that are slightly better than from PBE are obtained from the modified vdW-DFs. Although the tests reported here are for hard solids, not normally materials for which dispersion forces are thought to be important, we find a systematic improvement in cohesive properties for the alkali metals and alkali halides when nonlocal correlations are accounted for.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotVOlsbY%253D&md5=0e3350e5db3aa6fee4eadea9c6582255
  31. 31
    Becke, A. D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098– 3100,  DOI: 10.1103/PhysRevA.38.3098
    Google Scholar
    31
    Density-functional exchange-energy approximation with correct asymptotic behavior
    Becke, A. D.
    Physical Review A: Atomic, Molecular, and Optical Physics (1988), 38 (6), 3098-100CODEN: PLRAAN; ISSN:0556-2791.
    Current gradient-cor. d.-functional approxns. for the exchange energies of at. and mol. systems fail to reproduce the correct 1/r asymptotic behavior of the exchange-energy d. A gradient-cor. exchange-energy functional is given with the proper asymptotic limit. This functional, contg. only one parameter, fits the exact Hartree-Fock exchange energies of a wide variety of at. systems with remarkable accuracy, surpassing the performance of previous functionals contg. two parameters or more.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXmtlOhsLo%253D&md5=d4d219c134a5a90f689a8abed04d82cc
  32. 32
    Perdew, J. P.; Wang, Y. Accurate and simple analytic representation of the electron-gas correlation energy. Phys. Rev. B 1992, 45, 13244– 13249,  DOI: 10.1103/PhysRevB.45.13244
    Google Scholar
    32
    Accurate and simple analytic representation of the electron-gas correlation energy
    Perdew; Wang
    Physical review. B, Condensed matter (1992), 45 (23), 13244-13249 ISSN:0163-1829.
    There is no expanded citation for this reference.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sflvVWktw%253D%253D&md5=fd10f1e0ef650cbd66f7747322127295
  33. 33
    Dion, M.; Rydberg, H.; Schröder, E.; Langreth, D. C.; Lundqvist, B. I. Van der Waals Density Functional for General Geometries. Phys. Rev. Lett. 2004, 92, 246401,  DOI: 10.1103/PhysRevLett.92.246401
    Google Scholar
    33
    Van der Waals Density Functional for General Geometries
    Dion, M.; Rydberg, H.; Schroeder, E.; Langreth, D. C.; Lundqvist, B. I.
    Physical Review Letters (2004), 92 (24), 246401/1-246401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    A scheme within d. functional theory is proposed that provides a practical way to generalize to unrestricted geometries the method applied with some success to layered geometries [H. Rydberg et al., Phys. Rev. Lett. 91, 126402 (2003)]. It includes van der Waals forces in a seamless fashion. By expansion to second order in a carefully chosen quantity contained in the long-range part of the correlation functional, the nonlocal correlations are expressed in terms of a d.-d. interaction formula. It contains a relatively simple parametrized kernel, with parameters detd. by the local d. and its gradient. The proposed functional is applied to rare gas and benzene dimers, where it is shown to give a realistic description.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltVerur4%253D&md5=abbf50b023000f126ba66af15c786583
  34. 34
    Blöchl, P. E.; Jepsen, O.; Andersen, O. K. Improved tetrahedron method for Brillouin-zone integrations. Phys. Rev. B 1994, 49, 16223– 16233,  DOI: 10.1103/PhysRevB.49.16223
    Google Scholar
    34
    Improved tetrahedron method for Brillouin-zone integrations
    Blochl, Peter E.; Jepsen, O.; Andersen, O. K.
    Physical Review B: Condensed Matter and Materials Physics (1994), 49 (23), 16223-33CODEN: PRBMDO; ISSN:0163-1829.
    Several improvements of the tetrahedron method for Brillouin-zone integrations are presented. (1) A translational grid of k points and tetrahedra is suggested that renders the results for insulators identical to those obtained with special-point methods with the same no. of k points. (2) A simple correction formula goes beyond the linear approxn. of matrix elements within the tetrahedra and also improves the results for metals significantly. For a required accuracy this reduces the no. of k points by orders of magnitude. (3) Irreducible k points and tetrahedra are selected by a fully automated procedure, requiring as input only the space-group operations. (4) The integration is formulated as a weighted sum over irreducible k points with integration wts. calcd. using the tetrahedron method once for a given band structure. This allows an efficient use of the tetrahedron method also in plane-wave-based electronic-structure methods.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXks1Gqtb0%253D&md5=d1aa48b406bfccde3e58d26cbf21a809
  35. 35
    Schutte, W.; De Boer, J.; Jellinek, F. Crystal structures of tungsten disulfide and diselenide. J. Solid State Chem. 1987, 70, 207– 209,  DOI: 10.1016/0022-4596(87)90057-0
    Google Scholar
    35
    Crystal structures of tungsten disulfide and diselenide
    Schutte, W. J.; De Boer, J. L.; Jellinek, F.
    Journal of Solid State Chemistry (1987), 70 (2), 207-9CODEN: JSSCBI; ISSN:0022-4596.
    The crystal structures of WSe2 (space group P63/mmc) the 2H form (space group P63/mmc) and 3R form (space group R3m) of WS2 were refined from single-crystal data to R values of 6.9, 6.4, and 4.5%, resp. The interat. distances are compared with those in related compds.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXosFGqug%253D%253D&md5=1c965c42a2007ec83a4ac54de91e95a5
  36. 36
    Yan, A.; Chen, W.; Ophus, C.; Ciston, J.; Lin, Y.; Persson, K.; Zettl, A. Identifying different stacking sequences in few-layer CVD-grown MoS2 by low-energy atomic-resolution scanning transmission electron microscopy. Phys. Rev. B 2016, 93, 041420,  DOI: 10.1103/PhysRevB.93.041420
    Google Scholar
    36
    Identifying different stacking sequences in few-layer CVD-grown MoS2 by low-energy atomic-resolution scanning transmission electron microscopy
    Yan, Aiming; Chen, Wei; Ophus, Colin; Ciston, Jim; Lin, Yuyuan; Persson, Kristin; Zettl, Alex
    Physical Review B (2016), 93 (4), 041420/1-041420/5CODEN: PRBHB7; ISSN:2469-9950. (American Physical Society)
    Atomically thin MoS2 grown by chem. vapor deposition (CVD) is a promising candidate for next-generation electronics due to inherent CVD scalability and controllability. However, it is well known that the stacking sequence in few-layer MoS2 can significantly impact elec. and optical properties. Herein we report different intrinsic stacking sequences in CVD-grown few-layer MoS2 obtained by at.-resoln. annular-dark-field imaging in an aberration-cor. scanning transmission electron microscope operated at 50 keV. Trilayer MoS2 displays a new stacking sequence distinct from the commonly obsd. 2H and 3R phases of MoS2. D. functional theory is used to examine the stability of different stacking sequences, and the findings are consistent with our exptl. observations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Citr%252FL&md5=b77645f29f4f575ab71c03e9c3916dd6
  37. 37
    Pickett, W. E.; Krakauer, H.; Allen, P. B. Smooth Fourier interpolation of periodic functions. Phys. Rev. B 1988, 38, 2721– 2726,  DOI: 10.1103/PhysRevB.38.2721
    Google Scholar
    37
    Smooth Fourier interpolation of periodic functions
    Pickett; Krakauer; Allen
    Physical review. B, Condensed matter (1988), 38 (4), 2721-2726 ISSN:0163-1829.
    There is no expanded citation for this reference.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sfhtlemuw%253D%253D&md5=a73f53b08cb37b33c554c4435f9f44da
  38. 38
    Coutinho, S.; Tavares, M.; Barboza, C.; Frazão, N.; Moreira, E.; Azevedo, D. L. 3R and 2H polytypes of MoS2: DFT and DFPT calculations of structural, optoelectronic, vibrational and thermodynamic properties. J. Phys. Chem. Solids 2017, 111, 25– 33,  DOI: 10.1016/j.jpcs.2017.07.010
    Google Scholar
    38
    3R and 2H polytypes of MoS2: DFT and DFPT calculations of structural, optoelectronic, vibrational and thermodynamic properties
    Coutinho, S. S.; Tavares, M. S.; Barboza, C. A.; Frazao, N. F.; Moreira, E.; Azevedo, David L.
    Journal of Physics and Chemistry of Solids (2017), 111 (), 25-33CODEN: JPCSAW; ISSN:0022-3697. (Elsevier Ltd.)
    We report the results of a theor. study on the behavior of the structural, optoelectronic, vibrational, including IR and Raman theor. spectra, phonon spectrum, and thermodn. properties of 3R- and 2H- polytypes of molybdenum disulfide (MoS2) using d. functional theory (DFT) considering both the local d. and generalized gradient approxn., LDA and GGA, resp. Calcd. lattice parameters are close to the exptl. measurements, and an indirect band gap E(A→KΓ) = 1.33 eV (0.68 eV) was obtained within the GGA (LDA) level of calcn., considering the 3R-polytype, and for the 2H- polytype an indirect band gap E(Γ→KΓ) = 1.30 eV (0.70 eV) was obtained within the GGA (LDA) approxn. The complex dielec. function and absorption of 3R-MoS2 and 2H-MoS2 polytypes were shown to be sensitive to the plane of polarization of the incident light. The phonon dispersion relation together with d. of states (DOS) as well as theor. peaks of the IR (IR) and Raman spectra in the frequency range of 0-800 cm-1 was analyzed and assigned, considering the norm-conserved pseudopotentials. The thermodn. potentials, the sp. heat at const. vol. and Debye temp. of the 3R-MoS2 and 2H-MoS2 polytypes are also calcd., whose dependence on the temp. are discussed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1WrtL%252FP&md5=7c37ef72fdd6330abe2bdd64f5537562
  39. 39
    Setyawan, W.; Curtarolo, S. High-throughput electronic band structure calculations: Challenges and tools. Comput. Mater. Sci. 2010, 49, 299– 312,  DOI: 10.1016/j.commatsci.2010.05.010
    Google Scholar
    There is no corresponding record for this reference.
  40. 40
    Perez-Mato, J.; Orobengoa, D.; Tasci, E.; De la Flor Martin, G.; Kirov, A. Crystallography Online: Bilbao Crystallographic Server. Bulgarian Chem. Commun. 2011, 43, 183– 197
    Google Scholar
    40
    Crystallography online: Bilbao crystallographic server
    Aroyo, M. I.; Perez-Mato, J. M.; Orobengoa, D.; Tasci, E.; de la Flor, G.; Kirov, A.
    Bulgarian Chemical Communications (2011), 43 (2), 183-197CODEN: BCHCE4; ISSN:0324-1130. (Bulgarian Academy of Sciences)
    The Bilbao Crystallog. Server is a web site with crystallog. databases and programs available online. It was operating for more than ten years and new applications are being added regularly. The programs available on the server do not need a local installation and can be used free of charge. The server gives access to general information related to crystallog. symmetry groups (generators, general and special positions, maximal subgroups, Brillouin zones, etc.). Apart from the simple tools for retrieving the stored data, there are programs for the anal. of group-subgroup relations between space groups. There are also software package studying specific problems of solid-state physics, structural chem. and crystallog.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlaqs7rN&md5=d81dab069e4816ac6ec6184d8d960e1f
  41. 41
    Aroyo, M. I.; Perez-Mato, J. M.; Capillas, C.; Kroumova, E.; Ivantchev, S.; Madariaga, G.; Kirov, A.; Wondratschek, H. Bilbao Crystallographic Server: I. Databases and crystallographic computing programs. Zeitschrift für Kristallographie - Crystalline Materials 2006, 221, 15– 27,  DOI: 10.1524/zkri.2006.221.1.15
    Google Scholar
    There is no corresponding record for this reference.
  42. 42
    Aroyo, M. I.; Kirov, A.; Capillas, C.; Perez-Mato, J. M.; Wondratschek, H. Bilbao Crystallographic Server. II. Representations of crystallographic point groups and space groups. Acta Crystallogr., Sect. A 2006, 62, 115– 128,  DOI: 10.1107/S0108767305040286
    Google Scholar
    42
    Bilbao Crystallographic Server. II. Representations of crystallographic point groups and space groups
    Aroyo, Mois I.; Kirov, Asen; Capillas, Cesar; Perez-Mato, J. M.; Wondratschek, Hans
    Acta Crystallographica, Section A: Foundations of Crystallography (2006), A62 (2), 115-128CODEN: ACACEQ; ISSN:0108-7673. (Blackwell Publishing Ltd.)
    The Bilbao Crystallog. Server is a web site with crystallog. programs and databases freely available online (http://www.cryst.ehu.es). The server gives access to general information related to crystallog. symmetry groups (generators, general and special positions, maximal subgroups, Brillouin zones etc.). Apart from the simple tools for retrieving the stored data, there are programs for the anal. of group-subgroup relations between space groups (subgroups and supergroups, Wyckoff-position splitting schemes etc.). There are also software packages studying specific problems of solid-state physics, structural chem. and crystallog. This article reports on the programs treating representations of point and space groups. There are tools for the construction of irreducible representations, for the study of the correlations between representations of group-subgroup pairs of space groups and for the decompns. of Kronecker products of representations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhslWnur8%253D&md5=689fb23c14e777b10fed4390b438b9a9
  43. 43
    Aroyo, M. I.; Orobengoa, D.; de la Flor, G.; Tasci, E. S.; Perez-Mato, J. M.; Wondratschek, H. Brillouin-zone database on the Bilbao Crystallographic Server. Acta Crystallogr., Sect. A 2014, 70, 126– 137,  DOI: 10.1107/S205327331303091X
    Google Scholar
    43
    Brillouin-zone database on the Bilbao Crystallographic Server
    Aroyo, Mois I.; Orobengoa, Danel; de la Flor, Gemma; Tasci, Emre S.; Perez-Mato, J. Manuel; Wondratschek, Hans
    Acta Crystallographica, Section A: Foundations and Advances (2014), 70 (2), 126-137CODEN: ACSAD7; ISSN:2053-2733. (International Union of Crystallography)
    The Brillouin-zone database of the Bilbao Crystallog. Server () offers k-vector tables and figures which form the background of a classification of the irreducible representations of all 230 space groups. The symmetry properties of the wavevectors are described by the so-called reciprocal-space groups and this classification scheme is compared with the classification of Cracknell et al. [Kronecker Product Tables, Vol. 1, General Introduction and Tables of Irreducible Representations of Space Groups (1979). New York: IFI/Plenum]. The compilation provides a soln. to the problems of uniqueness and completeness of space-group representations by specifying the independent parameter ranges of general and special k vectors. Guides to the k-vector tables and figures explain the content and arrangement of the data. Recent improvements and modifications of the Brillouin-zone database, including new tables and figures for the trigonal, hexagonal and monoclinic space groups, are discussed in detail and illustrated by several examples.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXms1WrsL4%253D&md5=18ca33cbd86f9755a26750c617604421
  44. 44
    Tasci, E. S.; de la Flor, G.; Orobengoa, D.; Capillas, C.; Perez-Mato, J. M.; Aroyo, M. I. An introduction to the tools hosted in the Bilbao Crystallographic Server. EPJ. Web of Conferences 2012, 22, 00009,  DOI: 10.1051/epjconf/20122200009
    Google Scholar
    There is no corresponding record for this reference.
  45. 45
    Deslippe, J.; Samsonidze, G.; Strubbe, D. A.; Jain, M.; Cohen, M. L.; Louie, S. G. BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures. Comput. Phys. Commun. 2012, 183, 1269– 1289,  DOI: 10.1016/j.cpc.2011.12.006
    Google Scholar
    45
    BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures
    Deslippe, Jack; Samsonidze, Georgy; Strubbe, David A.; Jain, Manish; Cohen, Marvin L.; Louie, Steven G.
    Computer Physics Communications (2012), 183 (6), 1269-1289CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
    BerkeleyGW is a massively parallel computational package for electron excited-state properties that is based on the many-body perturbation theory employing the ab initio GW and GW plus Bethe-Salpeter equation methodol. It can be used in conjunction with many d.-functional theory codes for ground-state properties, including PARATEC, PARSEC, Quantum ESPRESSO, SIESTA, and Octopus. The package can be used to compute the electronic and optical properties of a wide variety of material systems from bulk semiconductors and metals to nanostructured materials and mols. The package scales to 10,000 s of CPUs and can be used to study systems contg. up to 100 s atoms.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XitVWmu7w%253D&md5=725a1f1a569d44c66759191d89b21ad3
  46. 46
    Gulans, A.; Kontur, S.; Meisenbichler, C.; Nabok, D.; Pavone, P.; Rigamonti, S.; Sagmeister, S.; Werner, U.; Draxl, C. Exciting: a full-potential all-electron package implementing density-functional theory and many-body perturbation theory. J. Phys.: Condens. Matter 2014, 26, 363202,  DOI: 10.1088/0953-8984/26/36/363202
    Google Scholar
    46
    Exciting: a full-potential all-electron package implementing density-functional theory and many-body perturbation theory
    Gulans, Andris; Kontur, Stefan; Meisenbichler, Christian; Nabok, Dmitrii; Pavone, Pasquale; Rigamonti, Santiago; Sagmeister, Stephan; Werner, Ute; Draxl, Claudia
    Journal of Physics: Condensed Matter (2014), 26 (36), 363202/1-363202/24, 24 pp.CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
    A review. Linearized augmented planewave methods are known as the most precise numerical schemes for solving the Kohn-Sham equations of d.-functional theory (DFT). In this review, we describe how this method is realized in the all-electron full-potential computer package, exciting. We emphasize the variety of different related basis sets, subsumed as (linearized) augmented planewave plus local orbital methods, discussing their pros and cons and we show that extremely high accuracy (microhartrees) can be achieved if the basis is chosen carefully. As the name of the code suggests, exciting is not restricted to ground-state calcns., but has a major focus on excited-state properties. It includes time-dependent DFT in the linear-response regime with various static and dynamical exchange-correlation kernels. These are preferably used to compute optical and electron-loss spectra for metals, mols. and semiconductors with weak electron-hole interactions. exciting makes use of many-body perturbation theory for charged and neutral excitations. To obtain the quasi-particle band structure, the GW approach is implemented in the single-shot approxn., known as G0W0. Optical absorption spectra for valence and core excitations are handled by the soln. of the Bethe-Salpeter equation, which allows for the description of strongly bound excitons. Besides these aspects concerning methodol., we demonstrate the broad range of possible applications by prototypical examples, comprising elastic properties, phonons, thermal-expansion coeffs., dielec. tensors and loss functions, magneto-optical Kerr effect, core-level spectra and more.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1ykur%252FL&md5=a067435218af2e121b53b9ce8f6c31e6
  47. 47
    Vorwerk, C.; Aurich, B.; Cocchi, C.; Draxl, C. Bethe-Salpeter equation for absorption and scattering spectroscopy: implementation in the exciting code. Electronic Structure 2019, 1, 037001,  DOI: 10.1088/2516-1075/ab3123
    Google Scholar
    47
    Bethe-Salpeter equation for absorption and scattering spectroscopy: implementation in the exciting code
    Vorwerk, Christian; Aurich, Benjamin; Cocchi, Caterina; Draxl, Claudia
    Electronic Structure (2019), 1 (3), 037001CODEN: ESLTAC; ISSN:2516-1075. (IOP Publishing Ltd.)
    The Bethe-Salpeter equation for the electron-hole correlation function is the state-of-the-art formalism for optical and core spectroscopy in condensed matter. Solns. of this equation yield the full dielec. response, including both the absorption and the inelastic scattering spectra. Here, we present an efficient implementation within the all-electron full-potential code exciting, which employs the linearized augmented plane-wave (L)APW + LO basis set. Being an all-electron code, exciting allows the calcn. of optical and core excitations on the same footing. The implementation fully includes the effects of finite momentum transfer which may occur in inelastic x-ray spectroscopy and electron energy-loss spectroscopy. Our implementation does not require the application of the Tamm-Dancoff approxn. that is commonly employed in the detn. of absorption spectra in condensed matter. The interface with parallel linear-algebra libraries enables the calcn. for complex systems. The capability of our implementation to compute, analyze, and interpret the results of different spectroscopic techniques is demonstrated by selected examples of prototypical inorg. and org. semiconductors and insulators.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvFagtb7K&md5=a26228fa534d49628981014a63a49ad6
  48. 48
    Ambrosch-Draxl, C.; Sofo, J. O. Linear optical properties of solids within the full-potential linearized augmented planewave method. Comput. Phys. Commun. 2006, 175, 1– 14,  DOI: 10.1016/j.cpc.2006.03.005
    Google Scholar
    48
    Linear optical properties of solids within the full-potential linearized augmented planewave method
    Ambrosch-Draxl, Claudia; Sofo, Jorge O.
    Computer Physics Communications (2006), 175 (1), 1-14CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
    We present a scheme for the calcn. of linear optical properties by the all-electron full-potential linearized augmented planewave (LAPW) method. A summary of the theor. background for the derivation of the dielec. tensor within the RPA is provided. The momentum matrix elements are evaluated in detail for the LAPW basis, and the interband as well as the intra-band contributions to the dielec. tensor are given. As an example the formalism is applied to Al. The program is available as a module within the WIEN2k code.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xltlegsbk%253D&md5=d5cd976cfcba1c49e0f3b78ed4d6440b
  49. 49
    Keast, V. An introduction to the calculation of valence EELS: Quantum mechanical methods for bulk solids. Micron 2013, 44, 93– 100,  DOI: 10.1016/j.micron.2012.08.001
    Google Scholar
    49
    An introduction to the calculation of valence EELS: Quantum mechanical methods for bulk solids
    Keast, V. J.
    Micron (2013), 44 (), 93-100CODEN: MCONEN; ISSN:0968-4328. (Elsevier Ltd.)
    A review. The low-loss region of the electron energy-loss spectrum, the valence EELS, provides information about the electronic structure and optical properties of materials. For bulk materials the spectral intensity can be directly connected to the complex dielec. function. Ab initio quantum mech. calcns. have an important role to play in the interpretation of the fine spectral detail and how this can be connected to the material properties. This paper provides an overview of theor. background to the calcn. of valence EELS in bulk solids and gives specific details on how to run such calcns. using the WIEN2k code. The comparison of Au and AuAl2 illustrates how in metals such calcns. are successful in reproducing the main spectral details and can be used to understand the origin of the different colors of these two metals.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVajtLzM&md5=3a8554f57e9e2ebcd1e5445fea4cf5f8
  50. 50
    Raether, H. Excitation of plasmons and interband transitions by electrons; Springer, 1980; Vol. 88, pp 19– 22.
    Google Scholar
    There is no corresponding record for this reference.
  51. 51
    Johari, P.; Shenoy, V. B. ”Tunable Dielectric Properties of Transition Metal Dichalcogenides. ACS Nano 2011, 5, 5903– 5908,  DOI: 10.1021/nn201698t
    Google Scholar
    51
    Tunable Dielectric Properties of Transition Metal Dichalcogenides
    Johari, Priya; Shenoy, Vivek B.
    ACS Nano (2011), 5 (7), 5903-5908CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Since discovery of graphene, layered materials have drawn considerable attention because of their possible exfoliation into single and multilayer 2-dimensional sheets. Because of strong surface effects, the properties of these materials vary drastically with the no. of layers in a sheet. The authors have performed 1st-principles d. functional based calcns. to evaluate the electron energy loss spectrum (EELS) of bulk, monolayer, and bilayer configurations of several transition metal dichalcogenides, which include semiconducting as well as metallic compds. The authors' study shows that the peaks in the EELS spectra move toward larger wavelengths (red shift) with the decrease in no. of layers. The π plasmon peak shifts slightly by 0.5-1.0 eV, while a significant shift of ∼5.5-13.0 eV was obtained for π + σ plasmon, when exfoliated from bulk to single-layer. This underscores the importance of the interlayer coupling on the loss spectra and the dielec. properties. The authors' results are in very good agreement with the recent measurements performed by Coleman et al. (Science2011, 331, 568).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotlGis7o%253D&md5=5275a9e222e519449dd03407a299d2c2

    PMID: 21707067.

  52. 52
    Gusakova, J.; Wang, X.; Shiau, L. L.; Krivosheeva, A.; Shaposhnikov, V.; Borisenko, V.; Gusakov, V.; Tay, B. K. ”Electronic Properties of Bulk and Monolayer TMDs: Theoretical Study Within DFT Framework (GVJ-2e Method). physica status solidi (a) 2017, 214, 1700218,  DOI: 10.1002/pssa.201700218
    Google Scholar
    There is no corresponding record for this reference.

Cited By

ARTICLE SECTIONS
Jump To

This article is cited by 5 publications.

  1. Abel Brokkelkamp, Jaco ter Hoeve, Isabel Postmes, Sabrya E. van Heijst, Louis Maduro, Albert V. Davydov, Sergiy Krylyuk, Juan Rojo, Sonia Conesa-Boj. Spatially Resolved Band Gap and Dielectric Function in Two-Dimensional Materials from Electron Energy Loss Spectroscopy. The Journal of Physical Chemistry A 2022, 126 (7) , 1255-1262. https://doi.org/10.1021/acs.jpca.1c09566
  2. Elie A. Moujaes, W.A. Diery, Arwa Albar. Buckling in novel graphene-like thoriumene and uraniumene monolayers: Electronic, mechanical, and optical properties from first-principles calculations. Materials Today Communications 2023, 34 , 105075. https://doi.org/10.1016/j.mtcomm.2022.105075
  3. Bernard Lalroliana, Lalmuanchhana, Lalhriatzuala. DFT + U study of electronic and optical properties of Cu3TMTe4: TM = V, Nb, Ta with incorporation of SOC. Materials Today: Proceedings 2023, 128 https://doi.org/10.1016/j.matpr.2023.01.197
  4. Elie A. Moujaes, W.A. Diery, Arwa Albar. Electronic, mechanical and optical properties of the new 1T dipolonide PdPo2 and PtPo2 monolayers: A comparative study with 1T Pd and Pt-based dichalcogenides. Physica E: Low-dimensional Systems and Nanostructures 2023, 146 , 115548. https://doi.org/10.1016/j.physe.2022.115548
  5. Mudasser Husain, Nasir Rahman, Hind Albalawi, Safa Ezzine, Mongi Amami, Tahir Zaman, Altaf Ur Rehman, Mohammad Sohail, Rajwali Khan, Abid Ali Khan, Tahir, Aurangzeb Khan. Examining computationally the structural, elastic, optical, and electronic properties of CaQCl 3 (Q = Li and K) chloroperovskites using DFT framework. RSC Advances 2022, 12 (50) , 32338-32349. https://doi.org/10.1039/D2RA05602J
Download PDF

  • Abstract

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 1

    Figure 1. Schematic for the different polytypes of WS2. In the top panels, it is shown how all three polytypes exhibit a hexagonal structure when viewed from the [0001] direction; (a) the 2H crystal phase exhibits a honeycomb lattice, while the (b) 3R and (c) 2H/3R polytypes both have an atom in the middle of their honeycomb structures. The stacking sequences of the 2H, 3R, and their mixed 2H/3R polytypes can be better assessed when viewed from a lateral viewpoint with respect to the layers, as illustrated in the bottom panels.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 2

    Figure 2. Left panels: the calculated density of states associated with the (a) 2H/3R, (c) 2H, and (e) 3R polytypes with and without spin–orbit coupling (SOC) taken into account. Right panels: the resulting band structures of the (b) 2H/3R, (d) 2H, and (f) 3R polytypes evaluated with and without SOC.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 3

    Figure 3. (a,b) Out-of-plane energy-loss function of the mixed 2H/3R polytype calculated on the DFT and GW level with and without taking spin–orbit coupling into account. (c,d) Experimental EELS measurements acquired on a WS2 nanostructure characterized by the same 2H/3R polytypism. Note that the zero-loss peak (ZLP) has not been subtracted from the EELS data in the bottom left panel.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 4

    Figure 4. Calculated joint density of states of the 2H/3R crystal structure with the GW framework without (a,b) and with (c,d) spin–orbit coupling effects taken into account. Here VB and CB stand for valence band and conduction band, respectively.

    High Resolution Image
    Download MS PowerPoint Slide

  • References

    ARTICLE SECTIONS
    Jump To

    This article references 52 other publications.

    1. 1
      Manzeli, S.; Ovchinnikov, D.; Pasquier, D.; Yazyev, O. V.; Kis, A. 2D transition metal dichalcogenides. Nature Reviews Materials 2017, 2, 17033,  DOI: 10.1038/natrevmats.2017.33
      Google Scholar
      1
      2D transition metal dichalcogenides
      Manzeli, Sajedeh; Ovchinnikov, Dmitry; Pasquier, Diego; Yazyev, Oleg V.; Kis, Andras
      Nature Reviews Materials (2017), 2 (2), 17033CODEN: NRMADL; ISSN:2058-8437. (Nature Publishing Group)
      A review. Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of at.-scale thickness, direct bandgap, strong spin-orbit coupling and favorable electronic and mech. properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examd. and their properties are discussed, with particular attention to their charge d. wave, superconductive and topol. phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVWmtr%252FO&md5=83d0f2b1adaae4e8cf09dceb3597f2da
    2. 2
      Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M. Band structure tunability in MoS2 under interlayer compression: A DFT and GW study. Phys. Rev. B 2013, 87, 245114,  DOI: 10.1103/PhysRevB.87.245114
      Google Scholar
      2
      Band structure tunability in MoS2 under interlayer compression: a DFT and GW study
      Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M.
      Physical Review B: Condensed Matter and Materials Physics (2013), 87 (24), 245114/1-245114/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The electronic band structures of MoS2 monolayer and 2H1 bulk polytype are studied within d.-functional theory (DFT) and many-body perturbation theory (GW approxn.). Interlayer van der Waals (vdW) interactions, responsible for bulk binding, are calcd. with the postprocessing Wannier functions method. From both fat bands and Wannier functions anal., it is shown that the transition from a direct band gap in the monolayer to an indirect band gap in bilayer or bulk systems is triggered by medium- to short-range electronic interactions between adjacent layers, which arise at the equil. interlayer distance detd. by the balance between vdW attraction and exchange repulsion. The semiconductor-to-semimetal (S-SM) transition is found from both theor. methods: around c = 10.7 Å and c = 9.9 Å for DFT and GW, resp. A metallic transition is also obsd. for the interlayer distance c = 9.7 Å. Dirac cone-like band structures and linear bands near Fermi level are found for shorter c lattice parameter values. The VdW correction to total energy was used to est. the pressure at which S-SM transition takes place from a fitting to a model equation of state.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1yms7fL&md5=89b3dd8bb0d22ea4720db63134fe9e30
    3. 3
      Johari, P.; Shenoy, V. B. Tunable Dielectric Properties of Transition Metal Dichalcogenides. ACS Nano 2011, 5, 5903– 5908,  DOI: 10.1021/nn201698t
      Google Scholar
      3
      Tunable Dielectric Properties of Transition Metal Dichalcogenides
      Johari, Priya; Shenoy, Vivek B.
      ACS Nano (2011), 5 (7), 5903-5908CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Since discovery of graphene, layered materials have drawn considerable attention because of their possible exfoliation into single and multilayer 2-dimensional sheets. Because of strong surface effects, the properties of these materials vary drastically with the no. of layers in a sheet. The authors have performed 1st-principles d. functional based calcns. to evaluate the electron energy loss spectrum (EELS) of bulk, monolayer, and bilayer configurations of several transition metal dichalcogenides, which include semiconducting as well as metallic compds. The authors' study shows that the peaks in the EELS spectra move toward larger wavelengths (red shift) with the decrease in no. of layers. The π plasmon peak shifts slightly by 0.5-1.0 eV, while a significant shift of ∼5.5-13.0 eV was obtained for π + σ plasmon, when exfoliated from bulk to single-layer. This underscores the importance of the interlayer coupling on the loss spectra and the dielec. properties. The authors' results are in very good agreement with the recent measurements performed by Coleman et al. (Science2011, 331, 568).
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotlGis7o%253D&md5=5275a9e222e519449dd03407a299d2c2

      PMID: 21707067.

    4. 4
      Ramasubramaniam, A.; Naveh, D.; Towe, E. Tunable band gaps in bilayer transition-metal dichalcogenides. Phys. Rev. B 2011, 84, 205325,  DOI: 10.1103/PhysRevB.84.205325
      Google Scholar
      4
      Tunable band gaps in bilayer transition-metal dichalcogenides
      Ramasubramaniam, Ashwin; Naveh, Doron; Towe, Elias
      Physical Review B: Condensed Matter and Materials Physics (2011), 84 (20), 205325/1-205325/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      We investigate band-gap tuning in bilayer transition-metal dichalcogenides by external elec. fields applied perpendicular to the layers. Using d. functional theory, we show that the fundamental band gap of MoS2, MoSe2, MoTe2, and WS2 bilayer structures continuously decreases with increasing applied elec. fields, eventually rendering them metallic. We interpret our results in the light of the giant Stark effect and obtain a robust relationship, which is essentially characterized by the interlayer spacing, for the rate of change of band gap with applied external field. Our study expands the known space of layered materials with widely tunable band gaps beyond the classic example of bilayer graphene and suggests potential directions for fabrication of novel electronic and photonic devices.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFKltb3P&md5=9a2422ff4fdc0a84f03b2653f9ccd13a
    5. 5
      Gusakova, J.; Wang, X.; Shiau, L. L.; Krivosheeva, A.; Shaposhnikov, V.; Borisenko, V.; Gusakov, V.; Tay, B. K. Electronic Properties of Bulk and Monolayer TMDs: Theoretical Study Within DFT Framework (GVJ-2e Method). physica status solidi (a) 2017, 214, 1700218,  DOI: 10.1002/pssa.201700218
      Google Scholar
      There is no corresponding record for this reference.
    6. 6
      Ryou, J.; Kim, Y.-S.; Kc, S.; Cho, K. Monolayer MoS2 Bandgap Modulation by Dielectric Environments and Tunable Bandgap Transistors. Sci. Rep. 2016, 6, 29184,  DOI: 10.1038/srep29184
      Google Scholar
      6
      Monolayer MoS2 Bandgap Modulation by Dielectric Environments and Tunable Bandgap Transistors
      Ryou, Junga; Kim, Yong-Sung; Kc, Santosh; Cho, Kyeongjae
      Scientific Reports (2016), 6 (), 29184CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Semiconductors with a moderate bandgap have enabled modern electronic device technol., and the current scaling trends down to nanometer scale have introduced two-dimensional (2D) semiconductors. The bandgap of a semiconductor has been an intrinsic property independent of the environments and detd. fundamental semiconductor device characteristics. In contrast to bulk semiconductors, we demonstrate that an atomically thin two-dimensional semiconductor has a bandgap with strong dependence on dielec. environments. Specifically, monolayer MoS2 bandgap is shown to change from 2.8 eV to 1.9 eV by dielec. environment. Utilizing the bandgap modulation property, a tunable bandgap transistor, which can be in general made of a two-dimensional semiconductor, is proposed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFCrs7fP&md5=67cab9e695232edf801552072ea7b991
    7. 7
      Eknapakul, T.; King, P. D. C.; Asakawa, M.; Buaphet, P.; He, R.-H.; Mo, S.-K.; Takagi, H.; Shen, K. M.; Baumberger, F.; Sasagawa, T.; Jungthawan, S.; Meevasana, W. Electronic Structure of a Quasi-Freestanding MoS2 Monolayer. Nano Lett. 2014, 14, 1312– 1316,  DOI: 10.1021/nl4042824
      Google Scholar
      7
      Electronic Structure of a Quasi-Freestanding MoS2 Monolayer
      Eknapakul, T.; King, P. D. C.; Asakawa, M.; Buaphet, P.; He, R.-H.; Mo, S.-K.; Takagi, H.; Shen, K. M.; Baumberger, F.; Sasagawa, T.; Jungthawan, S.; Meevasana, W.
      Nano Letters (2014), 14 (3), 1312-1316CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Several transition-metal dichalcogenides exhibit a striking crossover from indirect to direct band gap semiconductors as they are thinned down to a single monolayer. Here, we demonstrate how an electronic structure characteristic of the isolated monolayer can be created at the surface of a bulk MoS2 crystal. This is achieved by intercalating potassium in the interlayer van der Waals gap, expanding its size while simultaneously doping electrons into the conduction band. Our angle-resolved photoemission measurements reveal resulting electron pockets centered at the K and K' points of the Brillouin zone, providing the first momentum-resolved measurements of how the conduction band dispersions evolve to yield an approx. direct band gap of ∼1.8 eV in quasi-freestanding monolayer MoS2. As well as validating previous theor. proposals, this establishes a novel methodol. for manipulating electronic structure in transition-metal dichalcogenides, opening a new route for the generation of large-area quasi-freestanding monolayers for future fundamental study and use in practical applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXivFWitLg%253D&md5=94b25a41d45dc2f7ad339bf7291e9603

      PMID: 24552197.

    8. 8
      Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105, 136805,  DOI: 10.1103/PhysRevLett.105.136805
      Google Scholar
      8
      Atomically Thin MoS2. A New Direct-Gap Semiconductor
      Mak, Kin Fai; Lee, Changgu; Hone, James; Shan, Jie; Heinz, Tony F.
      Physical Review Letters (2010), 105 (13), 136805/1-136805/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      The electronic properties of ultrathin crystals of MoS2 consisting of N = 1, 2,...,6 S-Mo-S monolayers were investigated by optical spectroscopy. Through characterization by absorption, photoluminescence, and photocond. spectroscopy, we trace the effect of quantum confinement on the material's electronic structure. With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by >0.6 eV. This leads to a crossover to a direct-gap material in the limit of the single monolayer. Unlike the bulk material, the MoS2 monolayer emits light strongly. The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 104 compared with the bulk material.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Chs7zL&md5=f29a2e9692fc341d1b921f7862cf4c2a
    9. 9
      Xu, H.; Liu, S.; Ding, Z.; Tan, S. J. R.; Yam, K. M.; Bao, Y.; Nai, C. T.; Ng, M.-F.; Lu, J.; Zhang, C.; Loh, K. P. Oscillating edge states in one-dimensional MoS2 nanowires. Nat. Commun. 2016, 7, 12904,  DOI: 10.1038/ncomms12904
      Google Scholar
      9
      Oscillating edge states in one-dimensional MoS2 nanowires
      Xu, Hai; Liu, Shuanglong; Ding, Zijing; Tan, Sherman J. R.; Yam, Kah Meng; Bao, Yang; Nai, Chang Tai; Ng, Man-Fai; Lu, Jiong; Zhang, Chun; Loh, Kian Ping
      Nature Communications (2016), 7 (), 12904CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Reducing the dimensionality of transition metal dichalcogenides to one dimension opens it to structural and electronic modulation related to charge d. wave and quantum correlation effects arising from edge states. The greater flexibility of a mol. scale nanowire allows a strain-imposing substrate to exert structural and electronic modulation on it, leading to an interplay between the curvature-induced influences and intrinsic ground-state topol. Herein, the templated growth of MoS2 nanowire arrays consisting of the smallest stoichiometric MoS2 building blocks is investigated using scanning tunnelling microscopy and non-contact at. force microscopy. Our results show that lattice strain imposed on a nanowire causes the energy of the edge states to oscillate periodically along its length in phase with the period of the substrate topog. modulation. This periodic oscillation vanishes when individual MoS2 nanowires join to form a wider nanoribbon, revealing that the strain-induced modulation depends on in-plane rigidity, which increases with system size.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1ejsb7O&md5=01c89de4a0a6a7106ae216dbe43416d0
    10. 10
      Tinoco, M.; Maduro, L.; Masaki, M.; Okunishi, E.; Conesa-Boj, S. Strain-Dependent Edge Structures in MoS2 Layers. Nano Lett. 2017, 17, 7021– 7026,  DOI: 10.1021/acs.nanolett.7b03627
      Google Scholar
      10
      Strain-Dependent Edge Structures in MoS2 Layers
      Tinoco, Miguel; Maduro, Luigi; Masaki, Mukai; Okunishi, Eiji; Conesa-Boj, Sonia
      Nano Letters (2017), 17 (11), 7021-7026CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Edge structures are low-dimensional defects unavoidable in layered materials of the transition metal dichalcogenides (TMD) family. Among the various types of such structures, the armchair (AC) and zigzag (ZZ) edge types are the most common. It has been predicted that the presence of intrinsic strain localized along these edges structures can have direct implications for the customization of their electronic properties. However, pinning down the relation between local structure and electronic properties at these edges is challenging. Here, we quantify the local strain field that arises at the edges of MoS2 flakes by combining aberration-cor. transmission electron microscopy (TEM) with the geometrical-phase anal. (GPA) method. We also provide further insight on the possible effects of such edge strain on the resulting electronic behavior by means of electron energy loss spectroscopy (EELS) measurements. Our results reveal that the two-dominant edge structures, ZZ and AC, induce the formation of different amts. of localized strain fields. We also show that by varying the free edge curvature from concave to convex, compressive strain turns into tensile strain. These results pave the way toward the customization of edge structures in MoS2, which can be used to engineer the properties of layered materials and thus contribute to the optimization of the next generation of at.-scale electronic devices built upon them.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslSit7%252FJ&md5=9079372f62c9db37ca8013b39e95dd86

      PMID: 29064254.

    11. 11
      Tinoco, M.; Maduro, L.; Conesa-Boj, S. Metallic edge states in zig-zag vertically-oriented MoS2 nanowalls. Sci. Rep. 2019, 9, 15602,  DOI: 10.1038/s41598-019-52119-3
      Google Scholar
      11
      Metallic edge states in zig-zag vertically-oriented MoS2 nanowalls
      Tinoco Miguel; Maduro Louis; Conesa-Boj Sonia; Tinoco Miguel
      Scientific reports (2019), 9 (1), 15602 ISSN:.
      The remarkable properties of layered materials such as MoS2 strongly depend on their dimensionality. Beyond manipulating their dimensions, it has been predicted that the electronic properties of MoS2 can also be tailored by carefully selecting the type of edge sites exposed. However, achieving full control over the type of exposed edge sites while simultaneously modifying the dimensionality of the nanostructures is highly challenging. Here we adopt a top-down approach based on focus ion beam in order to selectively pattern the exposed edge sites. This strategy allows us to select either the armchair (AC) or the zig-zag (ZZ) edges in the MoS2 nanostructures, as confirmed by high-resolution transmission electron microscopy measurements. The edge-type dependence of the local electronic properties in these MoS2 nanostructures is studied by means of electron energy-loss spectroscopy measurements. This way, we demonstrate that the ZZ-MoS2 nanostructures exhibit clear fingerprints of their predicted metallic character. Our results pave the way towards novel approaches for the design and fabrication of more complex nanostructures based on MoS2 and related layered materials for applications in fields such as electronics, optoelectronics, photovoltaics, and photocatalysts.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3MjjtFCksQ%253D%253D&md5=98b8e981314b20d7b00f8577346bfd8d
    12. 12
      He, J.; Hummer, K.; Franchini, C. Stacking effects on the electronic and optical properties of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. Phys. Rev. B 2014, 89, 075409,  DOI: 10.1103/PhysRevB.89.075409
      Google Scholar
      12
      Stacking effects on the electronic and optical properties of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2
      He, Jiangang; Hummer, Kerstin; Franchini, Cesare
      Physical Review B: Condensed Matter and Materials Physics (2014), 89 (7), 075409/1-075409/11CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      Employing the RPA we investigate the binding energy and Van der Waals (vdW) interlayer spacing between the two layers of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2 for five different stacking patterns, and examine the stacking-induced modifications on the electronic and optical/excitonic properties within the GW approxn. with a priori inclusion of spin-orbit coupling and by solving the two-particle Bethe-Salpeter equation. Our results show that for all cases, the most stable stacking order is the high symmetry AA' type, distinctive of the bulklike 2H symmetry, followed by the AB stacking fault, typical of the 3R polytypism, which is by only 5 meV/formula unit less stable. The conduction band min. is always located in the midpoint between K and Γ, regardless of the stacking and chem. compn. All MX2 undergo an direct-to-indirect optical gap transition going from the monolayer to the bilayer regime. The stacking and the characteristic vdW interlayer distance mainly influence the valence band splitting at K and its relative energy with respect to Γ, as well as, the electron-hole binding energy and the values of the optical excitations.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlvFGmu7s%253D&md5=fc17f4973c3cc2f64745909f637ca006
    13. 13
      Suzuki, R.; Sakano, M.; Zhang, Y. J.; Akashi, R.; Morikawa, D.; Harasawa, A.; Yaji, K.; Kuroda, K.; Miyamoto, K.; Okuda, T.; Ishizaka, K.; Arita, R.; Iwasa, Y. Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry. Nat. Nanotechnol. 2014, 9, 611– 617,  DOI: 10.1038/nnano.2014.148
      Google Scholar
      13
      Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry
      Suzuki, R.; Sakano, M.; Zhang, Y. J.; Akashi, R.; Morikawa, D.; Harasawa, A.; Yaji, K.; Kuroda, K.; Miyamoto, K.; Okuda, T.; Ishizaka, K.; Arita, R.; Iwasa, Y.
      Nature Nanotechnology (2014), 9 (8), 611-617CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      The valley degree of freedom of electrons is attracting growing interest as a carrier of information in various materials, including graphene, diamond and monolayer transition-metal dichalcogenides. The monolayer transition-metal dichalcogenides are semiconducting and are unique due to the coupling between the spin and valley degrees of freedom originating from the relativistic spin-orbit interaction. Here, we report the direct observation of valley-dependent out-of-plane spin polarization in an archetypal transition-metal dichalcogenide-MoS2-using spin- and angle-resolved photoemission spectroscopy. The result is in fair agreement with a first-principles theor. prediction. This was made possible by choosing a 3R polytype crystal, which has a non-centrosym. structure, rather than the conventional centrosym. 2H form. We also confirm robust valley polarization in the 3R form by means of circularly polarized photoluminescence spectroscopy. Non-centrosym. transition-metal dichalcogenide crystals may provide a firm basis for the development of magnetic and elec. manipulation of spin/valley degrees of freedom.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1ait77K&md5=357d1a1ca0cc8ab246da538f40dbc5b3
    14. 14
      Chen, L.; Feng, H.; Zhang, R.; Wang, S.; Zhang, X.; Wei, Z.; Zhu, Y.; Gu, M.; Zhao, C. Phase-Controlled Synthesis of 2H/3R-MoSe2 Nanosheets on P-Doped Carbon for Synergistic Hydrogen Evolution. ACS Applied Nano Materials 2020, 3, 6516– 6523,  DOI: 10.1021/acsanm.0c00988
      Google Scholar
      14
      Phase-Controlled Synthesis of 2H/3R-MoSe2 Nanosheets on P-Doped Carbon for Synergistic Hydrogen Evolution
      Chen, Lunfeng; Feng, Hanghang; Zhang, Rui; Wang, Suhang; Zhang, Xueyan; Wei, Zhijie; Zhu, Yuanmin; Gu, Meng; Zhao, Chenyang
      ACS Applied Nano Materials (2020), 3 (7), 6516-6523CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
      The nanoscale structure of catalysts has a profound influence on their physicochem. properties. However, the controlled synthesis of desired highly active microstructures is still challenging. In this work, through the introduction of phytic acid (PA), MoSe2 nanosheets with 2H/3R heterophases are successfully synthesized on a P-doped carbon substrate. Plenty of defects are introduced into the basal plane of MoSe2 with largely expanded interlayer spacings, which increase the no. of active sites and enhance the electronic/ionic transport and mass transfer. Benefiting from these structure merits, the obtained heterostructure exhibits superior HER activity and durability. A low overpotential of 164 mV is obsd. at a c.d. of 10 mA cm-2 with a Tafel slope of 44 mV dec-1. The HER performance is well maintained even after 10 h tests, showing superior electrochem. robustness. This controlled synthesis 2H/3R heterophased MoSe2 can be extended to other transitional metal chalcogenides (TMDs) for diverse applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1yntbbO&md5=b97ce510f6cd3f5a0ade38b1c1a7b0ed
    15. 15
      Wilson, J.; Yoffe, A. The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties. Adv. Phys. 1969, 18, 193– 335,  DOI: 10.1080/00018736900101307
      Google Scholar
      15
      Transition metal dichalcogenides. Discussion and interpretation of the observed optical, electrical, and structural properties
      Wilson, John Anthony; Yoffe, Abraham D.
      Advances in Physics (1969), 18 (73), 193-335CODEN: ADPHAH; ISSN:0001-8732.
      The transition metal dichalcogenides are ∼60 in no. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to <1000 Å and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of elec. and structural data available to yield useful working band models that are in accord with a MO approach. Several special topics have arisen: these include excition screening, d-band-formation, the metal/insulator transition, magnetism, and supercond. in such compds. High-pressure work seems to offer a possibility for testing the recent theory of excitonic insulators.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXjs1Ogug%253D%253D&md5=727600599d9dd61a97a338cafb741394
    16. 16
      Lukowski, M. A.; Daniel, A. S.; Meng, F.; Forticaux, A.; Li, L.; Jin, S. Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets. J. Am. Chem. Soc. 2013, 135, 10274– 10277,  DOI: 10.1021/ja404523s
      Google Scholar
      16
      Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets
      Lukowski, Mark A.; Daniel, Andrew S.; Meng, Fei; Forticaux, Audrey; Li, Linsen; Jin, Song
      Journal of the American Chemical Society (2013), 135 (28), 10274-10277CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Promising catalytic activity from MoS2 in the H evolution reaction (HER) is attributed to active sites located along the edges of its 2-dimensional layered crystal structure, but its performance is limited by the d. and reactivity of active sites, poor elec. transport, and inefficient elec. contact to the catalyst. Here the authors report enhanced HER catalysis (an electrocatalytic c.d. of 10 mA/cm2 at a low overpotential of -187 mV vs. RHE and a Tafel slope of 43 mV/decade) from metallic nanosheets of 1T-MoS2 chem. exfoliated via Li intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Structural characterization and electrochem. studies confirmed that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics and low-loss elec. transport and possess a proliferated d. of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make these metallic nanosheets a highly competitive earth-abundant HER catalyst.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpvFagtbs%253D&md5=6757bf06d9618bc12361b7a72c4d468a
    17. 17
      Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 2013, 13, 6222– 6227,  DOI: 10.1021/nl403661s
      Google Scholar
      17
      Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction
      Voiry, Damien; Salehi, Maryam; Silva, Rafael; Fujita, Takeshi; Chen, Mingwei; Asefa, Tewodros; Shenoy, Vivek B.; Eda, Goki; Chhowalla, Manish
      Nano Letters (2013), 13 (12), 6222-6227CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The authors report chem. exfoliated MoS2 nanosheets with a high concn. of metallic 1T phase using a solvent free intercalation method. After removing the excess of neg. charges from the surface of the nanosheets, highly conducting 1T phase MoS2 nanosheets exhibit excellent catalytic activity toward the evolution of H with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS2, the activity of 2H MoS2 decreased, consistent with edge oxidn. However, 1T MoS2 remains unaffected after oxidn., suggesting that edges of the nanosheets are not the main active sites. The importance of elec. cond. of the 2 phases on the H evolution reaction activity was further confirmed by using C nanotubes to increase the cond. of 2H MoS2.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsl2nsLnN&md5=972adb681c83a77d8d04bd7315d38a92
    18. 18
      Acerce, M.; Voiry, D.; Chhowalla, M. Metallic 1T phase MoS2 nanosheets as supercapacitor electrode materials. Nat. Nanotechnol. 2015, 10, 313– 318,  DOI: 10.1038/nnano.2015.40
      Google Scholar
      18
      Metallic 1T phase MoS2 nanosheets as supercapacitor electrode materials
      Acerce, Muharrem; Voiry, Damien; Chhowalla, Manish
      Nature Nanotechnology (2015), 10 (4), 313-318CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      Efficient intercalation of ions in layered materials forms the basis of electrochem. energy storage devices such as batteries and capacitors. Recent research has focused on the exfoliation of layered materials and then restacking the two-dimensional exfoliated nanosheets to form electrodes with enhanced electrochem. response. Here, it is shown that chem. exfoliated nanosheets of MoS2 contg. a high concn. of the metallic 1T phase can electrochem. intercalate ions such as H+, Li+, Na+, and K+ with extraordinary efficiency and achieve capacitance values ranging from ∼400 to ∼700 F cm-3 in a variety of aq. electrolytes. It is also demonstrated that this material is suitable for high-voltage (3.5 V) operation in non-aq. org. electrolytes, showing prime volumetric energy and power d. values, coulombic efficiencies in excess of 95%, and stability over 5,000 cycles. As it is shown by X-ray diffraction anal., these favorable electrochem. properties of 1T MoS2 layers are mainly a result of their hydrophilicity and high elec. cond., as well as the ability of the exfoliated layers to dynamically expand and intercalate the various ions.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlt1aisr4%253D&md5=11ea2a3283936339127471a687184ca5
    19. 19
      Voiry, D.; Mohite, A.; Chhowalla, M. Phase engineering of transition metal dichalcogenides. Chem. Soc. Rev. 2015, 44, 2702– 2712,  DOI: 10.1039/C5CS00151J
      Google Scholar
      19
      Phase engineering of transition metal dichalcogenides
      Voiry, Damien; Mohite, Aditya; Chhowalla, Manish
      Chemical Society Reviews (2015), 44 (9), 2702-2712CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      Transition metal dichalcogenides (TMDs) represent a family of materials with versatile electronic, optical, and chem. properties. Most TMD bulk crystals are van der Waals solids with strong bonding within the plane but weak interlayer bonding. The individual layers can be readily isolated. Single layer TMDs possess intriguing properties that are ideal for both fundamental and technol. relevant research studies. We review the structure and phases of single and few layered TMDs. We also describe recent progress in phase engineering in TMDs. The ability to tune the chem. by choosing a unique combination of transition metals and chalcogen atoms along with controlling their properties by phase engineering allows new functionalities to be realized with TMDs.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmslGjtbo%253D&md5=3b535ac3387c345182c704fbfaad8d79
    20. 20
      Puretzky, A. A.; Liang, L.; Li, X.; Xiao, K.; Wang, K.; Mahjouri-Samani, M.; Basile, L.; Idrobo, J. C.; Sumpter, B. G.; Meunier, V.; Geohegan, D. B. Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations. ACS Nano 2015, 9, 6333– 6342,  DOI: 10.1021/acsnano.5b01884
      Google Scholar
      20
      Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations
      Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; Xiao, Kai; Wang, Kai; Mahjouri-Samani, Masoud; Basile, Leonardo; Idrobo, Juan Carlos; Sumpter, Bobby G.; Meunier, Vincent; Geohegan, David B.
      ACS Nano (2015), 9 (6), 6333-6342CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The tunable optoelectronic properties of stacked 2-dimensional (2D) crystal monolayers are detd. by their stacking orientation, order, and at. registry. Atomic-resoln. Z-contrast scanning TEM (AR-Z-STEM) and EELS can be used to det. the exact at. registration between different layers, in few-layer 2D stacks; however, fast optical characterization techniques are essential for rapid development of the field. Using 2- and 3-layer MoSe2 and WSe2 crystals synthesized by CVD, the generally unexplored low frequency (LF) Raman modes (<50 cm-1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the no. of layers, but also their stacking configurations. Ab initio calcns. and group theory anal. corroborate the exptl. assignments detd. by AR-Z-STEM, and the calcd. LF mode fingerprints are related to the 2D crystal symmetries.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXot1eht74%253D&md5=d49e4c1c87ebd0a4cca5f537de3204ad

      PMID: 25965878.

    21. 21
      Lee, J.-U.; Kim, K.; Han, S.; Ryu, G. H.; Lee, Z.; Cheong, H. Raman Signatures of Polytypism in Molybdenum Disulfide. ACS Nano 2016, 10, 1948– 1953,  DOI: 10.1021/acsnano.5b05831
      Google Scholar
      21
      Raman Signatures of Polytypism in Molybdenum Disulfide
      Lee, Jae-Ung; Kim, Kangwon; Han, Songhee; Ryu, Gyeong Hee; Lee, Zonghoon; Cheong, Hyeonsik
      ACS Nano (2016), 10 (2), 1948-1953CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Since the stacking order sensitively affects various phys. properties of layered materials, accurate detn. of the stacking order is important for studying the basic properties of these materials as well as for device applications. Because 2H-molybdenum disulfide (MoS2) is most common in nature, most studies so far have focused on 2H-MoS2. However, we found that the 2H, 3R, and mixed stacking sequences exist in few-layer MoS2 exfoliated from natural molybdenite crystals. The crystal structures are confirmed by HR-TEM measurements. The Raman signatures of different polytypes are investigated by using three different excitation energies that are nonresonant and resonant with A and C excitons, resp. The low-frequency breathing and shear modes show distinct differences for each polytype, whereas the high-frequency intralayer modes show little difference. For resonant excitations at 1.96 and 2.81 eV, distinct features are obsd. that enable detn. of the stacking order.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvFKqtA%253D%253D&md5=a2a594c067a4ad57ebb33228109ab5a4

      PMID: 26756836.

    22. 22
      van Heijst, S. E.; Mukai, M.; Okunishi, E.; Hashiguchi, H.; Roest, L. I.; Maduro, L.; Rojo, J.; Conesa-Boj, S. Illuminating the Electronic Properties of WS2 Polytypism with Electron Microscopy. Ann. Phys. 2021, 533, 2000499,  DOI: 10.1002/andp.202000499
      Google Scholar
      22
      Illuminating the Electronic Properties of WS2 Polytypism with Electron Microscopy
      van Heijst, Sabrya E.; Mukai, Masaki; Okunishi, Eiji; Hashiguchi, Hiroki; Roest, Laurien I.; Maduro, Louis; Rojo, Juan; Conesa-Boj, Sonia
      Annalen der Physik (Berlin, Germany) (2021), 533 (3), 2000499CODEN: ANPYA2; ISSN:0003-3804. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Tailoring the specific stacking sequence (polytypes) of layered materials represents a powerful strategy to identify and design novel phys. properties. While nanostructures built upon transition-metal dichalcogenides (TMDs) with either the 2H or 3R cryst. phases have been routinely studied, knowledge of TMD nanomaterials based on mixed 2H/3R polytypes is far more limited. In this work, mixed 2H/3R free-standing WS2 nanostructures displaying a flower-like configuration are fingerprinted by means of state-of-the-art transmission electron microscopy. Their rich variety of shape-morphol. configurations is correlated with relevant local electronic properties such as edge, surface, and bulk plasmons. Machine learning is deployed to establish that the 2H/3R polytype displays an indirect band gap of EBG=1.6-0.2+0.3eV. Further, high resoln. electron energy-loss spectroscopy reveals energy-gain peaks exhibiting a gain-to-loss ratio greater than unity, a property that can be exploited for cooling strategies of atomically-thin TMD nanostructures and devices built upon them. The findings of this work represent a stepping stone towards an improved understanding of TMD nanomaterials based on mixed cryst. phases.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXmtFGks7c%253D&md5=8595a00a11525c8b3934e62d9b07ee6a
    23. 23
      Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, B864– B871,  DOI: 10.1103/PhysRev.136.B864
      Google Scholar
      There is no corresponding record for this reference.
    24. 24
      Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133– A1138,  DOI: 10.1103/PhysRev.140.A1133
      Google Scholar
      There is no corresponding record for this reference.
    25. 25
      Roest, L. I.; van Heijst, S. E.; Maduro, L.; Rojo, J.; Conesa-Boj, S. Charting the low-loss region in electron energy loss spectroscopy with machine learning. Ultramicroscopy 2021, 222, 113202,  DOI: 10.1016/j.ultramic.2021.113202
      Google Scholar
      25
      Charting the low-loss region in electron energy loss spectroscopy with machine learning
      Roest, Laurien I.; van Heijst, Sabrya E.; Maduro, Louis; Rojo, Juan; Conesa-Boj, Sonia
      Ultramicroscopy (2021), 222 (), 113202CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)
      A review. Exploiting the information provided by electron energy-loss spectroscopy (EELS) requires reliable access to the low-loss region where the zero-loss peak (ZLP) often overwhelms the contributions assocd. to inelastic scatterings off the specimen. Here we deploy machine learning techniques developed in particle physics to realize a model-independent, multidimensional detn. of the ZLP with a faithful uncertainty est. This novel method is then applied to subtract the ZLP for EEL spectra acquired in flower-like WS2 nanostructures characterised by a 2H/3R mixed polytypism. From the resulting subtracted spectra we det. the nature and value of the bandgap of polytypic WS2, finding EBG = 1.6+0.3-0.2eV with a clear preference for an indirect bandgap. Further, we demonstrate how this method enables us to robustly identify excitonic transitions down to very small energy losses. Our approach has been implemented and made available in an open source YTHON package dubbed EELSfitter.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtlWgtr4%253D&md5=41d5503df893b94b57887789d4042230
    26. 26
      Jiang, H.; Gómez-Abal, R. I.; Li, X. Z.; Meisenbichler, C.; Ambrosch-Draxl, C.; Scheffler, M. FHI-gap: A GW code based on the all-electron augmented plane wave method. Comput. Phys. Commun. 2013, 184, 348– 366,  DOI: 10.1016/j.cpc.2012.09.018
      Google Scholar
      26
      FHI-gap: A GW code based on the all-electron augmented plane wave method
      Jiang, Hong; Gomez-Abal, Ricardo I.; Li, Xin-Zheng; Meisenbichler, Christian; Ambrosch-Draxl, Claudia; Scheffler, Matthias
      Computer Physics Communications (2013), 184 (2), 348-366CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
      The GW method has become the state-of-the-art approach for the first-principles description of the electronic quasi-particle band structure in cryst. solids. Most of the existing codes rely on pseudopotentials in which only valence electrons are treated explicitly. The pseudopotential method can be problematic for systems with localized d- or \\f\\-electrons, even for ground-state d.-functional theory (DFT) calcns. The situation can become more severe in \\GW\\ calcns., because pseudo-wavefunctions are used in the computation of the self-energy and the core-valence interaction is approximated at the DFT level. In this work, we present the package FHI-gap, an all-electron \\GW\\ implementation based on the full-potential linearized augmented planewave plus local orbital (LAPW) method. The FHI-gap code can handle core, semicore, and valence states on the same footing, which allows for a correct treatment of core-valence interaction. Moreover, it does not rely on any pseudopotential or frozen-core approxn. It is, therefore, able to handle a wide range of materials, irresp. of their compn. Test calcns. demonstrate the convergence behavior of the results with respect to various cut-off parameters. These include the size of the basis set that is used to expand the products of Kohn-Sham wavefunctions, the no. of \\k\\ points for the Brillouin zone integration, the no. of frequency points for the integration over the imaginary axis, and the no. of unoccupied states. At present, FHI-gap is linked to the WIEN2k code, and an implementation into the exciting code is in progress.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVCisb7L&md5=dfcaffb5622570a5985f7495c1d99ccc
    27. 27
      Jiang, H.; Blaha, P. GW with linearized augmented plane waves extended by high-energy local orbitals. Phys. Rev. B 2016, 93, 115203,  DOI: 10.1103/PhysRevB.93.115203
      Google Scholar
      27
      GW with linearized augmented plane waves extended by high-energy local orbitals
      Jiang, Hong; Blaha, Peter
      Physical Review B (2016), 93 (11), 115203/1-115203/11CODEN: PRBHB7; ISSN:2469-9950. (American Physical Society)
      Many-body perturbation theory in the GW approxn. is currently the most accurate and robust first- principles approach to det. the electronic band structure of weakly correlated insulating materials without any empirical input. Recent GW results for ZnO with more careful investigation of the convergence with respect to the no. of unoccupied states have led to heated debates regarding the numerical accuracy of previously reported GW results using either pseudopotential plane waves or all-electron linearized augmented plane waves (LAPWs). The latter has been arguably regarded as the most accurate scheme for electronic-structure theory for solids. This work aims to solve the ZnO puzzle via a systematic investigation of the effects of including high-energy local orbitals (HLOs) in the LAPW-based GW calcns. of semiconductors. Using ZnO as the prototypical example, it is shown that the inclusion of HLOs has two main effects: it improves the description of high-lying unoccupied states by reducing the linearization errors of the std. LAPW basis, and in addn. it provides an efficient way to achieve the completeness in the summation of states in GW calcns. By investigating the convergence of GW band gaps with respect to the no. of HLOs for several other typical examples, it was found that the effects of HLOs are highly system-dependent, and in most cases the inclusion of HLOs changes the band gap by less than 0.2 eV. Compared to its effects on the band gap, the consideration of HLOs has even stronger effects on the GW correction to the valence-band max., which is of great significance for the GW prediction of the ionization potentials of semiconductors. By considering an extended set of semiconductors with relatively well- established exptl. band gaps, it was found that in general using a HLO-enhanced LAPW basis significantly improves the agreement with expt. for both the band gap and the ionization potential, and overall the partially self-consistent GW0 approach based on the generalized gradient approxn. gives an optimal performance.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVShurnL&md5=56567295648e472ec2524e32ab908e8b
    28. 28
      Blaha, P.; Schwarz, K.; Tran, F.; Laskowski, R.; Madsen, G. K. H.; Marks, L. D. WIEN2k: An APW+lo program for calculating the properties of solids. J. Chem. Phys. 2020, 152, 074101,  DOI: 10.1063/1.5143061
      Google Scholar
      28
      WIEN2k: An APW+lo program for calculating the properties of solids
      Blaha, Peter; Schwarz, Karlheinz; Tran, Fabien; Laskowski, Robert; Madsen, Georg K. H.; Marks, Laurence D.
      Journal of Chemical Physics (2020), 152 (7), 074101CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The WIEN2k program is based on the APW plus local orbitals (APW + lo) method to solve the Kohn-Sham equations of d. functional theory. The APW + lo method, which considers all electrons (core and valence) self-consistently in a full-potential treatment, is implemented very efficiently in WIEN2k, since various types of parallelization are available and many optimized numerical libraries can be used. Many properties can be calcd., ranging from the basic ones, such as the electronic band structure or the optimized at. structure, to more specialized ones such as the NMR shielding tensor or the elec. polarization. After a brief presentation of the APW + lo method, we review the usage, capabilities, and features of WIEN2k (version 19) in detail. The various options, properties, and available approxns. for the exchange-correlation functional, as well as the external libraries or programs that can be used with WIEN2k, are mentioned. Refs. to relevant applications and some examples are also given. (c) 2020 American Institute of Physics.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjs1Kksbs%253D&md5=23465e0a29a40cfa996278efa98c642b
    29. 29
      Klimeš, J.; Bowler, D. R.; Michaelides, A. Chemical accuracy for the van der Waals density functional. J. Phys.: Condens. Matter 2010, 22, 022201,  DOI: 10.1088/0953-8984/22/2/022201
      Google Scholar
      29
      Chemical accuracy for the van der Waals density functional
      Klimes, Jiri; Bowler, David R.; Michaelides, Angelos
      Journal of Physics: Condensed Matter (2010), 22 (2), 022201/1-022201/5CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
      The non-local van der Waals d. functional (vdW-DF) of Dion et al is a very promising scheme for the efficient treatment of dispersion bonded systems. We show here that the accuracy of vdW-DF can be dramatically improved both for dispersion and hydrogen bonded complexes through the judicious selection of its underlying exchange functional. New and published exchange functionals are identified that deliver much better than chem. accuracy from vdW-DF for the S22 benchmark set of weakly interacting dimers and for water clusters. Improved performance for the adsorption of water on salt is also obtained.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFKitb8%253D&md5=37cca57a611ebd2fea99edd70d979091
    30. 30
      Klimeš, J. c. v.; Bowler, D. R.; Michaelides, A. Van der Waals density functionals applied to solids. Phys. Rev. B 2011, 83, 195131,  DOI: 10.1103/PhysRevB.83.195131
      Google Scholar
      30
      Van der Waals density functionals applied to solids
      Klimes, Jiri; Bowler, David R.; Michaelides, Angelos
      Physical Review B: Condensed Matter and Materials Physics (2011), 83 (19), 195131/1-195131/13CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The van der Waals d. functional (vdW-DF) of M. Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] is a promising approach for including dispersion in approx. d. functional theory exchange-correlation functionals. Indeed, an improved description of systems held by dispersion forces has been demonstrated in the literature. However, despite many applications, std. general tests on a broad range of materials including traditional "hard" matter such as metals, ionic compds., and insulators are lacking. Such tests are important not least because many of the applications of the vdW-DF method focus on the adsorption of atoms and mols. on the surfaces of solids. Here we calc. the lattice consts., bulk moduli, and atomization energies for a range of solids using the original vdW-DF and several of its offspring. We find that the original vdW-DF overestimates lattice consts. in a similar manner to how it overestimates binding distances for gas-phase dimers. However, some of the modified vdW functionals lead to av. errors which are similar to those of PBE or better. Likewise, atomization energies that are slightly better than from PBE are obtained from the modified vdW-DFs. Although the tests reported here are for hard solids, not normally materials for which dispersion forces are thought to be important, we find a systematic improvement in cohesive properties for the alkali metals and alkali halides when nonlocal correlations are accounted for.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotVOlsbY%253D&md5=0e3350e5db3aa6fee4eadea9c6582255
    31. 31
      Becke, A. D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098– 3100,  DOI: 10.1103/PhysRevA.38.3098
      Google Scholar
      31
      Density-functional exchange-energy approximation with correct asymptotic behavior
      Becke, A. D.
      Physical Review A: Atomic, Molecular, and Optical Physics (1988), 38 (6), 3098-100CODEN: PLRAAN; ISSN:0556-2791.
      Current gradient-cor. d.-functional approxns. for the exchange energies of at. and mol. systems fail to reproduce the correct 1/r asymptotic behavior of the exchange-energy d. A gradient-cor. exchange-energy functional is given with the proper asymptotic limit. This functional, contg. only one parameter, fits the exact Hartree-Fock exchange energies of a wide variety of at. systems with remarkable accuracy, surpassing the performance of previous functionals contg. two parameters or more.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXmtlOhsLo%253D&md5=d4d219c134a5a90f689a8abed04d82cc
    32. 32
      Perdew, J. P.; Wang, Y. Accurate and simple analytic representation of the electron-gas correlation energy. Phys. Rev. B 1992, 45, 13244– 13249,  DOI: 10.1103/PhysRevB.45.13244
      Google Scholar
      32
      Accurate and simple analytic representation of the electron-gas correlation energy
      Perdew; Wang
      Physical review. B, Condensed matter (1992), 45 (23), 13244-13249 ISSN:0163-1829.
      There is no expanded citation for this reference.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sflvVWktw%253D%253D&md5=fd10f1e0ef650cbd66f7747322127295
    33. 33
      Dion, M.; Rydberg, H.; Schröder, E.; Langreth, D. C.; Lundqvist, B. I. Van der Waals Density Functional for General Geometries. Phys. Rev. Lett. 2004, 92, 246401,  DOI: 10.1103/PhysRevLett.92.246401
      Google Scholar
      33
      Van der Waals Density Functional for General Geometries
      Dion, M.; Rydberg, H.; Schroeder, E.; Langreth, D. C.; Lundqvist, B. I.
      Physical Review Letters (2004), 92 (24), 246401/1-246401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      A scheme within d. functional theory is proposed that provides a practical way to generalize to unrestricted geometries the method applied with some success to layered geometries [H. Rydberg et al., Phys. Rev. Lett. 91, 126402 (2003)]. It includes van der Waals forces in a seamless fashion. By expansion to second order in a carefully chosen quantity contained in the long-range part of the correlation functional, the nonlocal correlations are expressed in terms of a d.-d. interaction formula. It contains a relatively simple parametrized kernel, with parameters detd. by the local d. and its gradient. The proposed functional is applied to rare gas and benzene dimers, where it is shown to give a realistic description.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltVerur4%253D&md5=abbf50b023000f126ba66af15c786583
    34. 34
      Blöchl, P. E.; Jepsen, O.; Andersen, O. K. Improved tetrahedron method for Brillouin-zone integrations. Phys. Rev. B 1994, 49, 16223– 16233,  DOI: 10.1103/PhysRevB.49.16223
      Google Scholar
      34
      Improved tetrahedron method for Brillouin-zone integrations
      Blochl, Peter E.; Jepsen, O.; Andersen, O. K.
      Physical Review B: Condensed Matter and Materials Physics (1994), 49 (23), 16223-33CODEN: PRBMDO; ISSN:0163-1829.
      Several improvements of the tetrahedron method for Brillouin-zone integrations are presented. (1) A translational grid of k points and tetrahedra is suggested that renders the results for insulators identical to those obtained with special-point methods with the same no. of k points. (2) A simple correction formula goes beyond the linear approxn. of matrix elements within the tetrahedra and also improves the results for metals significantly. For a required accuracy this reduces the no. of k points by orders of magnitude. (3) Irreducible k points and tetrahedra are selected by a fully automated procedure, requiring as input only the space-group operations. (4) The integration is formulated as a weighted sum over irreducible k points with integration wts. calcd. using the tetrahedron method once for a given band structure. This allows an efficient use of the tetrahedron method also in plane-wave-based electronic-structure methods.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXks1Gqtb0%253D&md5=d1aa48b406bfccde3e58d26cbf21a809
    35. 35
      Schutte, W.; De Boer, J.; Jellinek, F. Crystal structures of tungsten disulfide and diselenide. J. Solid State Chem. 1987, 70, 207– 209,  DOI: 10.1016/0022-4596(87)90057-0
      Google Scholar
      35
      Crystal structures of tungsten disulfide and diselenide
      Schutte, W. J.; De Boer, J. L.; Jellinek, F.
      Journal of Solid State Chemistry (1987), 70 (2), 207-9CODEN: JSSCBI; ISSN:0022-4596.
      The crystal structures of WSe2 (space group P63/mmc) the 2H form (space group P63/mmc) and 3R form (space group R3m) of WS2 were refined from single-crystal data to R values of 6.9, 6.4, and 4.5%, resp. The interat. distances are compared with those in related compds.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXosFGqug%253D%253D&md5=1c965c42a2007ec83a4ac54de91e95a5
    36. 36
      Yan, A.; Chen, W.; Ophus, C.; Ciston, J.; Lin, Y.; Persson, K.; Zettl, A. Identifying different stacking sequences in few-layer CVD-grown MoS2 by low-energy atomic-resolution scanning transmission electron microscopy. Phys. Rev. B 2016, 93, 041420,  DOI: 10.1103/PhysRevB.93.041420
      Google Scholar
      36
      Identifying different stacking sequences in few-layer CVD-grown MoS2 by low-energy atomic-resolution scanning transmission electron microscopy
      Yan, Aiming; Chen, Wei; Ophus, Colin; Ciston, Jim; Lin, Yuyuan; Persson, Kristin; Zettl, Alex
      Physical Review B (2016), 93 (4), 041420/1-041420/5CODEN: PRBHB7; ISSN:2469-9950. (American Physical Society)
      Atomically thin MoS2 grown by chem. vapor deposition (CVD) is a promising candidate for next-generation electronics due to inherent CVD scalability and controllability. However, it is well known that the stacking sequence in few-layer MoS2 can significantly impact elec. and optical properties. Herein we report different intrinsic stacking sequences in CVD-grown few-layer MoS2 obtained by at.-resoln. annular-dark-field imaging in an aberration-cor. scanning transmission electron microscope operated at 50 keV. Trilayer MoS2 displays a new stacking sequence distinct from the commonly obsd. 2H and 3R phases of MoS2. D. functional theory is used to examine the stability of different stacking sequences, and the findings are consistent with our exptl. observations.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Citr%252FL&md5=b77645f29f4f575ab71c03e9c3916dd6
    37. 37
      Pickett, W. E.; Krakauer, H.; Allen, P. B. Smooth Fourier interpolation of periodic functions. Phys. Rev. B 1988, 38, 2721– 2726,  DOI: 10.1103/PhysRevB.38.2721
      Google Scholar
      37
      Smooth Fourier interpolation of periodic functions
      Pickett; Krakauer; Allen
      Physical review. B, Condensed matter (1988), 38 (4), 2721-2726 ISSN:0163-1829.
      There is no expanded citation for this reference.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sfhtlemuw%253D%253D&md5=a73f53b08cb37b33c554c4435f9f44da
    38. 38
      Coutinho, S.; Tavares, M.; Barboza, C.; Frazão, N.; Moreira, E.; Azevedo, D. L. 3R and 2H polytypes of MoS2: DFT and DFPT calculations of structural, optoelectronic, vibrational and thermodynamic properties. J. Phys. Chem. Solids 2017, 111, 25– 33,  DOI: 10.1016/j.jpcs.2017.07.010
      Google Scholar
      38
      3R and 2H polytypes of MoS2: DFT and DFPT calculations of structural, optoelectronic, vibrational and thermodynamic properties
      Coutinho, S. S.; Tavares, M. S.; Barboza, C. A.; Frazao, N. F.; Moreira, E.; Azevedo, David L.
      Journal of Physics and Chemistry of Solids (2017), 111 (), 25-33CODEN: JPCSAW; ISSN:0022-3697. (Elsevier Ltd.)
      We report the results of a theor. study on the behavior of the structural, optoelectronic, vibrational, including IR and Raman theor. spectra, phonon spectrum, and thermodn. properties of 3R- and 2H- polytypes of molybdenum disulfide (MoS2) using d. functional theory (DFT) considering both the local d. and generalized gradient approxn., LDA and GGA, resp. Calcd. lattice parameters are close to the exptl. measurements, and an indirect band gap E(A→KΓ) = 1.33 eV (0.68 eV) was obtained within the GGA (LDA) level of calcn., considering the 3R-polytype, and for the 2H- polytype an indirect band gap E(Γ→KΓ) = 1.30 eV (0.70 eV) was obtained within the GGA (LDA) approxn. The complex dielec. function and absorption of 3R-MoS2 and 2H-MoS2 polytypes were shown to be sensitive to the plane of polarization of the incident light. The phonon dispersion relation together with d. of states (DOS) as well as theor. peaks of the IR (IR) and Raman spectra in the frequency range of 0-800 cm-1 was analyzed and assigned, considering the norm-conserved pseudopotentials. The thermodn. potentials, the sp. heat at const. vol. and Debye temp. of the 3R-MoS2 and 2H-MoS2 polytypes are also calcd., whose dependence on the temp. are discussed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1WrtL%252FP&md5=7c37ef72fdd6330abe2bdd64f5537562
    39. 39
      Setyawan, W.; Curtarolo, S. High-throughput electronic band structure calculations: Challenges and tools. Comput. Mater. Sci. 2010, 49, 299– 312,  DOI: 10.1016/j.commatsci.2010.05.010
      Google Scholar
      There is no corresponding record for this reference.
    40. 40
      Perez-Mato, J.; Orobengoa, D.; Tasci, E.; De la Flor Martin, G.; Kirov, A. Crystallography Online: Bilbao Crystallographic Server. Bulgarian Chem. Commun. 2011, 43, 183– 197
      Google Scholar
      40
      Crystallography online: Bilbao crystallographic server
      Aroyo, M. I.; Perez-Mato, J. M.; Orobengoa, D.; Tasci, E.; de la Flor, G.; Kirov, A.
      Bulgarian Chemical Communications (2011), 43 (2), 183-197CODEN: BCHCE4; ISSN:0324-1130. (Bulgarian Academy of Sciences)
      The Bilbao Crystallog. Server is a web site with crystallog. databases and programs available online. It was operating for more than ten years and new applications are being added regularly. The programs available on the server do not need a local installation and can be used free of charge. The server gives access to general information related to crystallog. symmetry groups (generators, general and special positions, maximal subgroups, Brillouin zones, etc.). Apart from the simple tools for retrieving the stored data, there are programs for the anal. of group-subgroup relations between space groups. There are also software package studying specific problems of solid-state physics, structural chem. and crystallog.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlaqs7rN&md5=d81dab069e4816ac6ec6184d8d960e1f
    41. 41
      Aroyo, M. I.; Perez-Mato, J. M.; Capillas, C.; Kroumova, E.; Ivantchev, S.; Madariaga, G.; Kirov, A.; Wondratschek, H. Bilbao Crystallographic Server: I. Databases and crystallographic computing programs. Zeitschrift für Kristallographie - Crystalline Materials 2006, 221, 15– 27,  DOI: 10.1524/zkri.2006.221.1.15
      Google Scholar
      There is no corresponding record for this reference.
    42. 42
      Aroyo, M. I.; Kirov, A.; Capillas, C.; Perez-Mato, J. M.; Wondratschek, H. Bilbao Crystallographic Server. II. Representations of crystallographic point groups and space groups. Acta Crystallogr., Sect. A 2006, 62, 115– 128,  DOI: 10.1107/S0108767305040286
      Google Scholar
      42
      Bilbao Crystallographic Server. II. Representations of crystallographic point groups and space groups
      Aroyo, Mois I.; Kirov, Asen; Capillas, Cesar; Perez-Mato, J. M.; Wondratschek, Hans
      Acta Crystallographica, Section A: Foundations of Crystallography (2006), A62 (2), 115-128CODEN: ACACEQ; ISSN:0108-7673. (Blackwell Publishing Ltd.)
      The Bilbao Crystallog. Server is a web site with crystallog. programs and databases freely available online (http://www.cryst.ehu.es). The server gives access to general information related to crystallog. symmetry groups (generators, general and special positions, maximal subgroups, Brillouin zones etc.). Apart from the simple tools for retrieving the stored data, there are programs for the anal. of group-subgroup relations between space groups (subgroups and supergroups, Wyckoff-position splitting schemes etc.). There are also software packages studying specific problems of solid-state physics, structural chem. and crystallog. This article reports on the programs treating representations of point and space groups. There are tools for the construction of irreducible representations, for the study of the correlations between representations of group-subgroup pairs of space groups and for the decompns. of Kronecker products of representations.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhslWnur8%253D&md5=689fb23c14e777b10fed4390b438b9a9
    43. 43
      Aroyo, M. I.; Orobengoa, D.; de la Flor, G.; Tasci, E. S.; Perez-Mato, J. M.; Wondratschek, H. Brillouin-zone database on the Bilbao Crystallographic Server. Acta Crystallogr., Sect. A 2014, 70, 126– 137,  DOI: 10.1107/S205327331303091X
      Google Scholar
      43
      Brillouin-zone database on the Bilbao Crystallographic Server
      Aroyo, Mois I.; Orobengoa, Danel; de la Flor, Gemma; Tasci, Emre S.; Perez-Mato, J. Manuel; Wondratschek, Hans
      Acta Crystallographica, Section A: Foundations and Advances (2014), 70 (2), 126-137CODEN: ACSAD7; ISSN:2053-2733. (International Union of Crystallography)
      The Brillouin-zone database of the Bilbao Crystallog. Server () offers k-vector tables and figures which form the background of a classification of the irreducible representations of all 230 space groups. The symmetry properties of the wavevectors are described by the so-called reciprocal-space groups and this classification scheme is compared with the classification of Cracknell et al. [Kronecker Product Tables, Vol. 1, General Introduction and Tables of Irreducible Representations of Space Groups (1979). New York: IFI/Plenum]. The compilation provides a soln. to the problems of uniqueness and completeness of space-group representations by specifying the independent parameter ranges of general and special k vectors. Guides to the k-vector tables and figures explain the content and arrangement of the data. Recent improvements and modifications of the Brillouin-zone database, including new tables and figures for the trigonal, hexagonal and monoclinic space groups, are discussed in detail and illustrated by several examples.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXms1WrsL4%253D&md5=18ca33cbd86f9755a26750c617604421
    44. 44
      Tasci, E. S.; de la Flor, G.; Orobengoa, D.; Capillas, C.; Perez-Mato, J. M.; Aroyo, M. I. An introduction to the tools hosted in the Bilbao Crystallographic Server. EPJ. Web of Conferences 2012, 22, 00009,  DOI: 10.1051/epjconf/20122200009
      Google Scholar
      There is no corresponding record for this reference.
    45. 45
      Deslippe, J.; Samsonidze, G.; Strubbe, D. A.; Jain, M.; Cohen, M. L.; Louie, S. G. BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures. Comput. Phys. Commun. 2012, 183, 1269– 1289,  DOI: 10.1016/j.cpc.2011.12.006
      Google Scholar
      45
      BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures
      Deslippe, Jack; Samsonidze, Georgy; Strubbe, David A.; Jain, Manish; Cohen, Marvin L.; Louie, Steven G.
      Computer Physics Communications (2012), 183 (6), 1269-1289CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
      BerkeleyGW is a massively parallel computational package for electron excited-state properties that is based on the many-body perturbation theory employing the ab initio GW and GW plus Bethe-Salpeter equation methodol. It can be used in conjunction with many d.-functional theory codes for ground-state properties, including PARATEC, PARSEC, Quantum ESPRESSO, SIESTA, and Octopus. The package can be used to compute the electronic and optical properties of a wide variety of material systems from bulk semiconductors and metals to nanostructured materials and mols. The package scales to 10,000 s of CPUs and can be used to study systems contg. up to 100 s atoms.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XitVWmu7w%253D&md5=725a1f1a569d44c66759191d89b21ad3
    46. 46
      Gulans, A.; Kontur, S.; Meisenbichler, C.; Nabok, D.; Pavone, P.; Rigamonti, S.; Sagmeister, S.; Werner, U.; Draxl, C. Exciting: a full-potential all-electron package implementing density-functional theory and many-body perturbation theory. J. Phys.: Condens. Matter 2014, 26, 363202,  DOI: 10.1088/0953-8984/26/36/363202
      Google Scholar
      46
      Exciting: a full-potential all-electron package implementing density-functional theory and many-body perturbation theory
      Gulans, Andris; Kontur, Stefan; Meisenbichler, Christian; Nabok, Dmitrii; Pavone, Pasquale; Rigamonti, Santiago; Sagmeister, Stephan; Werner, Ute; Draxl, Claudia
      Journal of Physics: Condensed Matter (2014), 26 (36), 363202/1-363202/24, 24 pp.CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
      A review. Linearized augmented planewave methods are known as the most precise numerical schemes for solving the Kohn-Sham equations of d.-functional theory (DFT). In this review, we describe how this method is realized in the all-electron full-potential computer package, exciting. We emphasize the variety of different related basis sets, subsumed as (linearized) augmented planewave plus local orbital methods, discussing their pros and cons and we show that extremely high accuracy (microhartrees) can be achieved if the basis is chosen carefully. As the name of the code suggests, exciting is not restricted to ground-state calcns., but has a major focus on excited-state properties. It includes time-dependent DFT in the linear-response regime with various static and dynamical exchange-correlation kernels. These are preferably used to compute optical and electron-loss spectra for metals, mols. and semiconductors with weak electron-hole interactions. exciting makes use of many-body perturbation theory for charged and neutral excitations. To obtain the quasi-particle band structure, the GW approach is implemented in the single-shot approxn., known as G0W0. Optical absorption spectra for valence and core excitations are handled by the soln. of the Bethe-Salpeter equation, which allows for the description of strongly bound excitons. Besides these aspects concerning methodol., we demonstrate the broad range of possible applications by prototypical examples, comprising elastic properties, phonons, thermal-expansion coeffs., dielec. tensors and loss functions, magneto-optical Kerr effect, core-level spectra and more.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1ykur%252FL&md5=a067435218af2e121b53b9ce8f6c31e6
    47. 47
      Vorwerk, C.; Aurich, B.; Cocchi, C.; Draxl, C. Bethe-Salpeter equation for absorption and scattering spectroscopy: implementation in the exciting code. Electronic Structure 2019, 1, 037001,  DOI: 10.1088/2516-1075/ab3123
      Google Scholar
      47
      Bethe-Salpeter equation for absorption and scattering spectroscopy: implementation in the exciting code
      Vorwerk, Christian; Aurich, Benjamin; Cocchi, Caterina; Draxl, Claudia
      Electronic Structure (2019), 1 (3), 037001CODEN: ESLTAC; ISSN:2516-1075. (IOP Publishing Ltd.)
      The Bethe-Salpeter equation for the electron-hole correlation function is the state-of-the-art formalism for optical and core spectroscopy in condensed matter. Solns. of this equation yield the full dielec. response, including both the absorption and the inelastic scattering spectra. Here, we present an efficient implementation within the all-electron full-potential code exciting, which employs the linearized augmented plane-wave (L)APW + LO basis set. Being an all-electron code, exciting allows the calcn. of optical and core excitations on the same footing. The implementation fully includes the effects of finite momentum transfer which may occur in inelastic x-ray spectroscopy and electron energy-loss spectroscopy. Our implementation does not require the application of the Tamm-Dancoff approxn. that is commonly employed in the detn. of absorption spectra in condensed matter. The interface with parallel linear-algebra libraries enables the calcn. for complex systems. The capability of our implementation to compute, analyze, and interpret the results of different spectroscopic techniques is demonstrated by selected examples of prototypical inorg. and org. semiconductors and insulators.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvFagtb7K&md5=a26228fa534d49628981014a63a49ad6
    48. 48
      Ambrosch-Draxl, C.; Sofo, J. O. Linear optical properties of solids within the full-potential linearized augmented planewave method. Comput. Phys. Commun. 2006, 175, 1– 14,  DOI: 10.1016/j.cpc.2006.03.005
      Google Scholar
      48
      Linear optical properties of solids within the full-potential linearized augmented planewave method
      Ambrosch-Draxl, Claudia; Sofo, Jorge O.
      Computer Physics Communications (2006), 175 (1), 1-14CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
      We present a scheme for the calcn. of linear optical properties by the all-electron full-potential linearized augmented planewave (LAPW) method. A summary of the theor. background for the derivation of the dielec. tensor within the RPA is provided. The momentum matrix elements are evaluated in detail for the LAPW basis, and the interband as well as the intra-band contributions to the dielec. tensor are given. As an example the formalism is applied to Al. The program is available as a module within the WIEN2k code.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xltlegsbk%253D&md5=d5cd976cfcba1c49e0f3b78ed4d6440b
    49. 49
      Keast, V. An introduction to the calculation of valence EELS: Quantum mechanical methods for bulk solids. Micron 2013, 44, 93– 100,  DOI: 10.1016/j.micron.2012.08.001
      Google Scholar
      49
      An introduction to the calculation of valence EELS: Quantum mechanical methods for bulk solids
      Keast, V. J.
      Micron (2013), 44 (), 93-100CODEN: MCONEN; ISSN:0968-4328. (Elsevier Ltd.)
      A review. The low-loss region of the electron energy-loss spectrum, the valence EELS, provides information about the electronic structure and optical properties of materials. For bulk materials the spectral intensity can be directly connected to the complex dielec. function. Ab initio quantum mech. calcns. have an important role to play in the interpretation of the fine spectral detail and how this can be connected to the material properties. This paper provides an overview of theor. background to the calcn. of valence EELS in bulk solids and gives specific details on how to run such calcns. using the WIEN2k code. The comparison of Au and AuAl2 illustrates how in metals such calcns. are successful in reproducing the main spectral details and can be used to understand the origin of the different colors of these two metals.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVajtLzM&md5=3a8554f57e9e2ebcd1e5445fea4cf5f8
    50. 50
      Raether, H. Excitation of plasmons and interband transitions by electrons; Springer, 1980; Vol. 88, pp 19– 22.
      Google Scholar
      There is no corresponding record for this reference.
    51. 51
      Johari, P.; Shenoy, V. B. ”Tunable Dielectric Properties of Transition Metal Dichalcogenides. ACS Nano 2011, 5, 5903– 5908,  DOI: 10.1021/nn201698t
      Google Scholar
      51
      Tunable Dielectric Properties of Transition Metal Dichalcogenides
      Johari, Priya; Shenoy, Vivek B.
      ACS Nano (2011), 5 (7), 5903-5908CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Since discovery of graphene, layered materials have drawn considerable attention because of their possible exfoliation into single and multilayer 2-dimensional sheets. Because of strong surface effects, the properties of these materials vary drastically with the no. of layers in a sheet. The authors have performed 1st-principles d. functional based calcns. to evaluate the electron energy loss spectrum (EELS) of bulk, monolayer, and bilayer configurations of several transition metal dichalcogenides, which include semiconducting as well as metallic compds. The authors' study shows that the peaks in the EELS spectra move toward larger wavelengths (red shift) with the decrease in no. of layers. The π plasmon peak shifts slightly by 0.5-1.0 eV, while a significant shift of ∼5.5-13.0 eV was obtained for π + σ plasmon, when exfoliated from bulk to single-layer. This underscores the importance of the interlayer coupling on the loss spectra and the dielec. properties. The authors' results are in very good agreement with the recent measurements performed by Coleman et al. (Science2011, 331, 568).
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotlGis7o%253D&md5=5275a9e222e519449dd03407a299d2c2

      PMID: 21707067.

    52. 52
      Gusakova, J.; Wang, X.; Shiau, L. L.; Krivosheeva, A.; Shaposhnikov, V.; Borisenko, V.; Gusakov, V.; Tay, B. K. ”Electronic Properties of Bulk and Monolayer TMDs: Theoretical Study Within DFT Framework (GVJ-2e Method). physica status solidi (a) 2017, 214, 1700218,  DOI: 10.1002/pssa.201700218
      Google Scholar
      There is no corresponding record for this reference.

  • Supporting Information

    Supporting Information

    ARTICLE SECTIONS
    Jump To

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsphyschemau.1c00038.

    • Figures illustrating geometrical optimization of the 2H/3R, 2H, and 3R structures; the primitive Brillouin zone of the 2H, 3R, and mixed 2H/3R crystalline phases of WS2; a magnified image of the band structure of the 2H and 2H/3R crystal phases near the Fermi energy; and additional details about the computational methods(PDF)


    Terms & Conditions

    Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

PDF [ 4MB]

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

You’ve supercharged your research process with ACS and Mendeley!

STEP 1:
Click to create an ACS ID

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

MENDELEY PAIRING EXPIRED
Your Mendeley pairing has expired. Please reconnect