Adsorption Study of a Water Molecule on Vacancy-Defected Nonpolar CdS SurfacesClick to copy article linkArticle link copied!
Abstract
A detailed understanding of the water–semiconductor interface is of major importance for elucidating the molecular interactions at the photocatalyst’s surface. Here, we studied the effect of vacancy defects on the adsorption of a water molecule on the (101̅0) and (112̅0) CdS surfaces, using spin-polarized density functional theory. We observed that the local spin polarization did not persist for most of the cationic vacancies on the surfaces, unlike in bulk, owing to surface reconstructions caused by displaced S atoms. This result suggests that cationic vacancies on these surfaces may not be the leading cause of the experimentally observed magnetism in CdS nanostructures. The surface vacancies are predominantly nonmagnetic except for one case, where a magnetic cationic vacancy is relatively stable due to constraints posed by the (101̅0) surface geometry. At this particular magnetic defect site, we found a very strong interaction with the H2O molecule leading to a case of chemisorption, where the local spin polarization vanishes concurrently. At the same defect site, adsorption of an O2 molecule was also simulated, and the results were found to be consistent with experimental electron paramagnetic resonance findings for powdered CdS. The anion vacancies on these surfaces were always found to be nonmagnetic and did not affect the water adsorption at these surfaces.
Introduction
Computational Methods
Results and Discussion
Bulk VCd and VS
Figure 1
Figure 1. (a) and (b) Spin-resolved density of states for the VCd in bulk CdS and for the two cases of C3v and Td configurations, respectively (M = magnetic, NM = nonmagnetic). In (c) the net spin density is shown for the C3v case, with an isosurface of 1 × 10–3e/Å3. The Cd atoms are plotted in magenta and S atoms in yellow.
Surface VCd and VS
(101̅0) Surface
Figure 2
Figure 2. (a), (b), and (c) Top views of the cation-defected (101̅0) surface (and subsurface); (d), (e), and (f) are the same for the (112̅0) surface. The colored isosurfaces are net spin densities with an isosurface of 1 × 10–3e/Å3 for the magnetic (M) cases. In the nonmagnetic (NM) cases, we can see the formation of S-dimers which stabilize the surface. The layer below (in white) is the atomic layer below the first subsurface.
Figure 3
Figure 3. (a) and (b) Summarize the relative stability for the vacancies with the same stoichiometry on the (101̅0) and (112̅0) surfaces. The most stable Cd-type and S-type defects are placed lowest (set to zero on the vertical axis). Magnetic vacancies are displayed in green and nonmagnetic vacancies in black.
(112̅0) Surface
Adsorption of Water Molecule on the Surfaces
(101̅0) Surface
Figure 4
Figure 4. (a) Charge difference density plot of the most stable H2O adsorption configuration on the clean (101̅0) surface and the (b) same for the (112̅0) surface. An isosurface of charge density of 4.7 × 10–4e/Å3 is used where the blue color indicates charge depletion and green indicates charge accumulation. The inset shows the LDOS for the H2O molecule, which indicates the case of physical adsorption.
Figure 5
Figure 5. (a), (b), (c) are the charge density difference plots for metastable geometries of adsorption of the H2O molecule on (101̅0) surface, and (d) and (e) are the same for the (112̅0) surface. An isosurface of charge density of 4.7 × 10–4e/Å3 is used. The insets in (a), (d), and (e) show the change in geometry upon relaxing with the vdW-optB88 functional; (b) and (c) do not show any changes in their geometry.
(112̅0) Surface
Effect of vdW Interaction
EadsPBE (eV) | EadsvdW (eV) | |
---|---|---|
(101̅0) | ||
Figure 4(a) | 0.62 | 0.79 |
Figure 5(a) | 0.21 | 0.39a |
Figure 5(b) | 0.23 | 0.36 |
Figure 5(c) | 0.26 | 0.39a |
(112̅0) | ||
Figure 4(b) | 0.53 | 0.70 |
Figure 5(d) | 0.40 | 0.68a |
Figure 5(e) | 0.09 | 0.68a |
Converged to the same geometry.
Adsorption on Surface VCd and VS
At the Magnetic Vacancy Sites
VCd1 on (101̅0)
Figure 6
Figure 6. The above configuration represents the interaction of water with the magnetic cation vacancy site leading to chemisorption (Eads = 1.48 eV), where the water molecule becomes a part of the surface. Chemisorption of H2O at the (101̅0) VCd1 site leads to neutralizing of the surface magnetic moment. The inset on the left shows the local DOS of the adsorbed H2O and the surface-S site to which the molecule is bonded, which shows the splitting of H2O molecular orbitals (1b2 and 3a1) and forming of new O–S bonds instead. The inset at the right shows a top view of the charge density difference plot (isosurface = 10–3e/Å3), where it is seen that the symmetry of the surface assists the H2O to bond.
VCd2 on (101̅0)
Figure 7
Figure 7. (a) and (b) Show the adsorption geometries for a water molecule on M and NM in the case of VCd2 on (101̅0). (c) and (d) show the same for NM cases of VCd1 and VCd2 of the (112̅0) surface.
VCd1 on (112̅0)
At Nonmagnetic Vacancy Sites
At VS Sites
Figure 8
Figure 8. (a), (b) H2O adsorption geometries on VS1 and VS2 defects of the (101̅0) surface, and (c) and (d) are the same for the (112̅0) surface.
Adsorption of O2 the Molecule on the VCd1 Defect of the (101̅0) Surface
Figure 9
Figure 9. Columns (a), (b), and (c) represent the characteristics of the converged geometries that were obtained for the O2 molecule adsorption at the VCd1 magnetic site on the (101̅0) surface. The two O atoms of the oxygen molecule are referred to as O1 and O2 atoms of the molecule, as shown in geometry (a). The first row indicates their respective charge difference plots of the configurations. The second row shows the spin-resolved LDOS for the configurations, indicating the two O atoms and surface S atom which bonds to the molecule. The third row shows the net spin density for these configurations. In the nonmagnetic case of (b) the local and the spin densities are zero and not shown here.
Conclusion
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.6b13010.
(I) Local DOS of S atoms neighboring the VCd in bulk CdS (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.
Acknowledgment
S.S.G. would like to thank Wun Fan Li and Xiaobin Xie for helpful discussions and comments on the manuscript. M.A.v.H. acknowledges support from The Netherlands Organization for Scientific Research (NWO) for a VIDI (Grant No. 723.012.006) and from the European Research Council (ERC Consolidator Grant No. 683076 NANO-INSITU). This work is part of the Industrial Partnership Programme “Computational Sciences for Energy Research” (Grant No. 13CSER067) of the NWO-I. This research program is cofinanced by Shell Global Solutions International B.V.
References
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- 22Fischer, G.; Sanchez, N.; Adeagbo, W.; Szotek, Z.; Temmerman, W. M.; Ernst, A.; Hoffmann, M.; Hergert, W.; Muñoz, M. C. Ab Initio Study of the p-Hole Magnetism at Polar Surfaces of ZnO: The Role of Correlations J. Phys.: Condens. Matter 2016, 28, 016003 DOI: 10.1088/0953-8984/28/1/016003Google ScholarThere is no corresponding record for this reference.
- 23Coey, M.; Ackland, K.; Venkatesan, M.; Sen, S. Collective Magnetic Response of CeO2 Nanoparticles Nat. Phys. 2016, 12, 694– 699 DOI: 10.1038/nphys3676Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjsFenu7Y%253D&md5=022b24899431fcb3d0e095ba8801270dCollective magnetic response of CeO2 nanoparticlesCoey, Michael; Ackland, Karl; Venkatesan, Munuswamy; Sen, SiddharthaNature Physics (2016), 12 (7), 694-699CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)The magnetism of nanoparticles and thin films of wide-bandgap oxides that include no magnetic cations is an unsolved puzzle. Progress has been hampered by both the irreproducibility of much of the exptl. data, and the lack of any generally accepted theor. explanation. The characteristic signature is a virtually anhysteretic, temp.-independent magnetization curve that sats. in an applied field that is several orders of magnitude greater than the magnetization. It would seem as if a tiny vol. fraction, .ltorsim.0.1%, of the samples is magnetic and that the energy scale is unusually high for spin magnetism. Here we investigate the effect of dispersing 4 nm CeO2 nanoparticles with powders of γAl2O3, sugar or latex microspheres. The satn. magnetization, Ms ≈ 60 A m-1 for compact samples, is maximized by 1 wt% lanthanum doping. Dispersing the CeO2 nanopowder reduces its magnetic moment by up to an order of magnitude, and there is a characteristic length scale of order 100 nm for the magnetism to appear in CeO2 nanoparticle clusters. The phenomenon is explained in terms of a giant orbital paramagnetism that appears in coherent mesoscopic domains due to resonant interaction with zero-point fluctuations of the vacuum electromagnetic field. The theory explains the obsd. temp.-independent magnetization curve and its doping and dispersion dependence, based on a length scale of 300 nm that corresponds to the wavelength of a max. in the UV absorption spectrum of the magnetic CeO2 nanoparticles. The coherent domains occupy roughly 10% of the sample vol.
- 24Kaewmaraya, T.; Pathak, B.; Araujo, C. M.; Rosa, A. L.; Ahuja, R. Water Adsorption on ZnO(1010): The Role of Intrinsic Defects Europhys. Lett. 2012, 97, 17014 DOI: 10.1209/0295-5075/97/17014Google ScholarThere is no corresponding record for this reference.
- 25Giacopetti, L.; Satta, A. Degradation of Cd-Yellow Paints: Ab Initio Study Of Native Defects in 10.0 Surface CdS Microchem. J. 2016, 126, 214– 219 DOI: 10.1016/j.microc.2015.12.005Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVKrtb3N&md5=322da49ea235c8e0f78bac00ecc6d129Degradation of Cd-yellow paints: Ab initio study of native defects in {10.0} surface CdSGiacopetti, Laura; Satta, AlessandraMicrochemical Journal (2016), 126 (), 214-219CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)Relevant effects produced at the surface of modern paintings include the growth of discolored crusts. In the specific case of cadmium yellow paints (CdS), white globular compds. mostly formed by hydrated cadmium sulfate and cadmium carbonate are obsd. The origins of such chem. and phys. alterations are still under debate. Structural defects in CdS, among other possible causes like photo-oxidn. processes, may play a role in the degrdn. process. Their presence in the pigment surface alters the electronic structure of cadmium sulfide by forming acceptor levels in the gap of the semiconductor. Such levels make the surface more reactive in the interaction with external agents (oxygen, water...). To this end, we present a theor. study of point defects, namely Cd- and S-vacancies, in the {10.0} CdS surface. The geometrical and electronic structures as well as the vacancy formation energies are detd. with the use of a first method. All the calcns. are performed within the framework of the d. functional theory (DFT) in the Generalized Gradient Approxn. (GGA-PBE) with the use of ultrasoft pseudopotentials.
- 26Giacopetti, L.; Satta, A. Degradation of Cd-Yellow Paints: Ab Initio Study of the Adsorption of Oxygen and Water on 10.0 CdS Surface J. Phys.: Conf. Ser. 2014, 566, 012021 DOI: 10.1088/1742-6596/566/1/012021Google ScholarThere is no corresponding record for this reference.
- 27Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects Phys. Rev. 1965, 140, A1133– A1138 DOI: 10.1103/PhysRev.140.A1133Google ScholarThere is no corresponding record for this reference.
- 28Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations For Metals and Semiconductors Using a Plane-Wave Basis Set Comput. Mater. Sci. 1996, 6, 15– 50 DOI: 10.1016/0927-0256(96)00008-0Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmtFWgsrk%253D&md5=779b9a71bbd32904f968e39f39946190Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis setKresse, G.; Furthmuller, J.Computational Materials Science (1996), 6 (1), 15-50CODEN: CMMSEM; ISSN:0927-0256. (Elsevier)The authors present a detailed description and comparison of algorithms for performing ab-initio quantum-mech. calcns. using pseudopotentials and a plane-wave basis set. The authors will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temp. d.-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N2atoms scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge d. including a new special preconditioning optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. The authors have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio mol.-dynamics package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
- 29Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169– 11186 DOI: 10.1103/PhysRevB.54.11169Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xms1Whu7Y%253D&md5=9c8f6f298fe5ffe37c2589d3f970a697Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis setKresse, G.; Furthmueller, J.Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
- 30Nishidate, K.; Sato, T.; Matsukura, Y.; Baba, M.; Hasegawa, M.; Sasaki, T. Density-Functional Electronic Structure Calculations for Native Defects and Cu Impurities in CdS Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 035210 DOI: 10.1103/PhysRevB.74.035210Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XotFWhu7s%253D&md5=2a6e06fdec795e001735a45a89d1f26dDensity-functional electronic structure calculations for native defects and Cu impurities in CdSNishidate, Kazume; Sato, Takuya; Matsukura, Yuta; Baba, Mamoru; Hasegawa, Masayuki; Sasaki, TaizoPhysical Review B: Condensed Matter and Materials Physics (2006), 74 (3), 035210/1-035210/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We performed d.-functional electronic structure calcns. for wurtzite CdS with native defects and Cu impurity. We investigate formation energies and ionization levels of the defects in various charge states. Our results reveal that the S vacancy is a double donor with the strongly localized orbital at the defect site, and could act as an intrinsic compensation defect under p-type doping. On the other hand, the interstitial S at the tetrahedral site is a double acceptor which forms into a dumbbell-like at. configuration with the nearest S atom. The impurity Cu substituting Cd produces a single acceptor state, while the interstitial Cu generates a single donor state. The calcd. formation energies imply that the donor state could also cause the compensation in the Cu doped CdS.
- 31Adachi, S. Properties of Group-IV, III-V and II-VI Semiconductors; John Wiley & Sons, Ltd.: New York, 2005; pp 1– 21.Google ScholarThere is no corresponding record for this reference.
- 32Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple Phys. Rev. Lett. 1996, 77, 3865– 3868 DOI: 10.1103/PhysRevLett.77.3865Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630Generalized gradient approximation made simplePerdew, John P.; Burke, Kieron; Ernzerhof, MatthiasPhysical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
- 33Klimes, J.; Bowler, D. R.; Michaelides, A. Chemical Accuracy for the Van Der Waals Density Functional J. Phys.: Condens. Matter 2010, 22, 022201 DOI: 10.1088/0953-8984/22/2/022201Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFKitb8%253D&md5=37cca57a611ebd2fea99edd70d979091Chemical accuracy for the van der Waals density functionalKlimes, Jiri; Bowler, David R.; Michaelides, AngelosJournal 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.
- 34Klimes, J.; Bowler, D. R.; Michaelides, A. Van der Waals Density Functionals Applied to Solids Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 195131 DOI: 10.1103/PhysRevB.83.195131Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotVOlsbY%253D&md5=0e3350e5db3aa6fee4eadea9c6582255Van der Waals density functionals applied to solidsKlimes, Jiri; Bowler, David R.; Michaelides, AngelosPhysical 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.
- 35Wei, S.-H.; Zunger, A. Role of Metal D States in II-VI Semiconductors Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 8958– 8981 DOI: 10.1103/PhysRevB.37.8958Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXkvVSjsrk%253D&md5=4a52c17c7dabbdc3b5fe4eb181336e72Role of metal d states in II-VI semiconductorsWei, S. H.; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (1988), 37 (15), 8958-81CODEN: PRBMDO; ISSN:0163-1829.All-electron band-structure calcns. and photoemission expts. on II-VI semiconductors both exhibit a metal d subband inside the main valence band. It has nevertheless been customary in pseudopotential and tight-binding approaches to neglect the metal d band by choosing Hamiltonian parameters which place this band inside the chem. inert at. cores. By using all-electron self-consistent electronic-structure techniques (which treat the outermost d electrons in the same way as other valence electrons) and by comparing the results to those obtained by methods which remove the d band from the valence spectrum, the effects on valence properties were studied. For II-VI semiconductors p-d repulsion and hybridization (1) lower the band gaps, (2) reduce the cohesive energy, (3) increase the equil. lattice parameters, (4) reduce the spin-orbit splitting, (5) alter the sign of the crystal-field splitting, (6) increase the valence-band offset between common-anion II-VI semiconductors, and (7) modify the charge distributions of various II-VI systems and their alloys. P-d repulsion is also responsible for the occurrence of deep Cu acceptor levels in II-VI semiconductors (compared with shallow acceptors of Zn in III-V), for the anomalously small band gaps in chalcopyrites, and for the neg. exchange splitting in ferromagnetic MnTe.
- 36Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P. Electron-Energy-Loss Spectra and the Structural Stability of Nickel Oxide: An LSDA+U Study Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 57, 1505– 1509 DOI: 10.1103/PhysRevB.57.1505Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXlsVarsQ%253D%253D&md5=9b4f0473346679cb1a8dce0ad7583153Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA+U studyDudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P.Physical Review B: Condensed Matter and Materials Physics (1998), 57 (3), 1505-1509CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)By taking better account of electron correlations in the 3d shell of metal ions in Ni oxide it is possible to improve the description of both electron energy loss spectra and parameters characterizing the structural stability of the material compared with local spin d. functional theory.
- 37Vesely, C. J.; Hengehold, R. L.; Langer, D. W. Uv Photoemission Measurements of the Upper D Levels in the IIB-VIA Compounds Phys. Rev. B 1972, 5, 2296– 2301 DOI: 10.1103/PhysRevB.5.2296Google ScholarThere is no corresponding record for this reference.
- 38Monkhorst, H. J.; Pack, J. D. Special Points For Brillouin-Zone Integrations Phys. Rev. B 1976, 13, 5188– 5192 DOI: 10.1103/PhysRevB.13.5188Google ScholarThere is no corresponding record for this reference.
- 39Lany, S. Semiconductor Thermochemistry in Density Functional Calculations Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 78, 245207 DOI: 10.1103/PhysRevB.78.245207Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXitlWmuw%253D%253D&md5=64766d7d38bd31f6986b9b20bc0a5637Semiconductor thermochemistry in density functional calculationsLany, StephanPhysical Review B: Condensed Matter and Materials Physics (2008), 78 (24), 245207/1-245207/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The local-d. and generalized gradient approxns. (LDA and GGA) to d. functional theory (DFT) exhibit incomplete error cancellation when energy differences are taken between chem. dissimilar systems. This energy inconsistency is manifested, e.g., in the tendency to underestimate the heat (enthalpy) of formation of semiconducting and insulating compds. in LDA and, even more so, in GGA. Considering a set of 61 compds. that can be formed from 14 elements (cations: Cu, Mg, Ca, Zn, Cd, Al, Ga, and In; anions: N, P, As, O, S, and Se), optimized elemental ref. energies are detd. by least-squares error minimization of an overdetd. set of linear equations. These elemental energies are "optimally consistent" with the DFT energies of the semiconductor compds. and imply corrections of up to 1 eV compared to the resp. LDA or GGA energies. While these "corrections" are not to be understood to yield the correct abs. total energies of the elements, they are proposed to give appropriate bounds for the chem. potentials for thermodn. processes in semiconductors and insulators, such as, e.g., defect formation, surface reconstruction, or catalytic processes. The present model allows to evaluate thermodn. processes using DFT energy differences taken only between systems that are expected to show good error cancellation.
- 40Implementation of Van der Waals Density Functional Approach to the Spin-Polarized System: Interaction Potential between Oxygen Molecules. J. Phys. Soc. Jpn. 2013, 82, 093701.Google ScholarThere is no corresponding record for this reference.
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Abstract
Figure 1
Figure 1. (a) and (b) Spin-resolved density of states for the VCd in bulk CdS and for the two cases of C3v and Td configurations, respectively (M = magnetic, NM = nonmagnetic). In (c) the net spin density is shown for the C3v case, with an isosurface of 1 × 10–3e/Å3. The Cd atoms are plotted in magenta and S atoms in yellow.
Figure 2
Figure 2. (a), (b), and (c) Top views of the cation-defected (101̅0) surface (and subsurface); (d), (e), and (f) are the same for the (112̅0) surface. The colored isosurfaces are net spin densities with an isosurface of 1 × 10–3e/Å3 for the magnetic (M) cases. In the nonmagnetic (NM) cases, we can see the formation of S-dimers which stabilize the surface. The layer below (in white) is the atomic layer below the first subsurface.
Figure 3
Figure 3. (a) and (b) Summarize the relative stability for the vacancies with the same stoichiometry on the (101̅0) and (112̅0) surfaces. The most stable Cd-type and S-type defects are placed lowest (set to zero on the vertical axis). Magnetic vacancies are displayed in green and nonmagnetic vacancies in black.
Figure 4
Figure 4. (a) Charge difference density plot of the most stable H2O adsorption configuration on the clean (101̅0) surface and the (b) same for the (112̅0) surface. An isosurface of charge density of 4.7 × 10–4e/Å3 is used where the blue color indicates charge depletion and green indicates charge accumulation. The inset shows the LDOS for the H2O molecule, which indicates the case of physical adsorption.
Figure 5
Figure 5. (a), (b), (c) are the charge density difference plots for metastable geometries of adsorption of the H2O molecule on (101̅0) surface, and (d) and (e) are the same for the (112̅0) surface. An isosurface of charge density of 4.7 × 10–4e/Å3 is used. The insets in (a), (d), and (e) show the change in geometry upon relaxing with the vdW-optB88 functional; (b) and (c) do not show any changes in their geometry.
Figure 6
Figure 6. The above configuration represents the interaction of water with the magnetic cation vacancy site leading to chemisorption (Eads = 1.48 eV), where the water molecule becomes a part of the surface. Chemisorption of H2O at the (101̅0) VCd1 site leads to neutralizing of the surface magnetic moment. The inset on the left shows the local DOS of the adsorbed H2O and the surface-S site to which the molecule is bonded, which shows the splitting of H2O molecular orbitals (1b2 and 3a1) and forming of new O–S bonds instead. The inset at the right shows a top view of the charge density difference plot (isosurface = 10–3e/Å3), where it is seen that the symmetry of the surface assists the H2O to bond.
Figure 7
Figure 7. (a) and (b) Show the adsorption geometries for a water molecule on M and NM in the case of VCd2 on (101̅0). (c) and (d) show the same for NM cases of VCd1 and VCd2 of the (112̅0) surface.
Figure 8
Figure 8. (a), (b) H2O adsorption geometries on VS1 and VS2 defects of the (101̅0) surface, and (c) and (d) are the same for the (112̅0) surface.
Figure 9
Figure 9. Columns (a), (b), and (c) represent the characteristics of the converged geometries that were obtained for the O2 molecule adsorption at the VCd1 magnetic site on the (101̅0) surface. The two O atoms of the oxygen molecule are referred to as O1 and O2 atoms of the molecule, as shown in geometry (a). The first row indicates their respective charge difference plots of the configurations. The second row shows the spin-resolved LDOS for the configurations, indicating the two O atoms and surface S atom which bonds to the molecule. The third row shows the net spin density for these configurations. In the nonmagnetic case of (b) the local and the spin densities are zero and not shown here.
References
This article references 40 other publications.
- 1Morales-Acevedo, A. Thin Film CdS/CdTe Solar Cells: Research Perspectives Sol. Energy 2006, 80, 675– 681 DOI: 10.1016/j.solener.2005.10.0081https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XltFOrurs%253D&md5=65add6808718bf39e4fd52bd0e181e15Thin film CdS/CdTe solar cells: Research perspectivesMorales-Acevedo, ArturoSolar Energy (2006), 80 (6), 675-681CODEN: SRENA4; ISSN:0038-092X. (Elsevier Ltd.)A review. Polycryst. thin film CdTe continues to be a leading material for the development of cost effective and reliable photovoltaics. The two key properties of this material are its band gap (1.5 eV), close to the ideal for photovoltaic conversion efficiency (1.45 eV), and its high optical absorption coeff. Thin-film CdTe solar cells are typically heterojunctions with CdS being the n-type partner, or window layer. Efficiencies as high as 16.5% have been achieved, but still there is some potential for increasing them. We make an anal. of the typical CdS/CdTe superstrate solar cell, and from it we establish crit. issues and different lines of research in order to improve the current efficiencies. We also show that present record efficiencies are very close to the practical efficiency limit for a CdS/CdTe heterojunction cell.
{SREN} ′05 - Solar Renewable Energy News Conference.
- 2Emin, S.; Fanetti, M.; Abdi, F. F.; Lisjak, D.; Valant, M.; van de Krol, R.; Dam, B. Photoelectrochemical Properties of Cadmium Chalcogenide-Sensitized Textured Porous Zinc Oxide Plate Electrodes ACS Appl. Mater. Interfaces 2013, 5, 1113– 1121 DOI: 10.1021/am30279862https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnvVCnsQ%253D%253D&md5=e65a81a3512aa8102d9c0b688ec22b61Photoelectrochemical Properties of Cadmium Chalcogenide-Sensitized Textured Porous Zinc Oxide Plate ElectrodesEmin, Saim; Fanetti, Mattia; Abdi, Fatwa F.; Lisjak, Darja; Valant, Matjaz; van de Krol, Roel; Dam, BernardACS Applied Materials & Interfaces (2013), 5 (3), 1113-1121CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)The authors report the photoelectrochem. (PEC) performance of textured porous ZnO and CdX-coated ZnO films (X = S, Se). Porous ZnO films were grown with a platelike morphol. on F-doped SnO2 (FTO) substrates. The growth of ZnO films involves a two-step procedure. In the 1st step, the authors electrochem. grew simonkolleite (Zn5(OH)8Cl2·H2O) plate films. Annealing of the simonkolleite at 450° results in textured porous ZnO films. The as-obtained porous ZnO electrodes were then used in PEC studies. To increase the light-harvesting efficiency, the authors sensitized these ZnO electrodes with CdS and CdSe quantum dots, using the so-called successive ion layer adsorption and reaction (SILAR) method. As expected, the photocurrent d. systematically increases when going from ZnO to ZnO/CdS to ZnO/CdSe. The highest photocurrent, ∼3.1 mA/cm2 at 1.2 V vs. RHE, was obtained in the CdSe-sensitized ZnO electrodes, because of their enhanced absorption in the visible range. Addnl., quantum efficiency values ≤90% were achieved with the textured porous ZnO films. Both CdS and CdSe-sensitized textured porous ZnO electrodes could be potentially useful materials in light-harvesting applications.
- 3Chen, X.; Shen, S.; Guo, L.; Mao, S. S. Semiconductor-Based Photocatalytic Hydrogen Generation Chem. Rev. 2010, 110, 6503– 6570 DOI: 10.1021/cr10016453https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtl2lsbvE&md5=6da42a404c342a1c69c2b65da103f31eSemiconductor-based Photocatalytic Hydrogen GenerationChen, Xiaobo; Shen, Shaohua; Guo, Liejin; Mao, Samuel S.Chemical Reviews (Washington, DC, United States) (2010), 110 (11), 6503-6570CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review on semiconductor-based photocatalytic hydrogen generation through water splitting. It starts with a brief introduction to semiconductor-based photocatalysts for hydrogen generation from water splitting, and then provides an overview of the development of high-efficiency, visible-light-driven photocatalysts. A no. of synthetic and modification techniques for adjusting the band structure to harvest visible light and improve the charge sepn. in photocatalysis are discussed. Photocatalytic systems for water splitting are also reviewed and classified into two main kinds: sacrificial reagent-contg. water-splitting systems and overall water-splitting systems.
- 4Amirav, L.; Alivisatos, A. P. Photocatalytic Hydrogen Production with Tunable Nanorod Heterostructures J. Phys. Chem. Lett. 2010, 1, 1051– 1054 DOI: 10.1021/jz100075c4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXivV2mtLk%253D&md5=27f57bc8cf7289d5708f225de873967dPhotocatalytic Hydrogen Production with Tunable Nanorod HeterostructuresAmirav, Lilac; Alivisatos, A. PaulJournal of Physical Chemistry Letters (2010), 1 (7), 1051-1054CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The authors report the design of a multicomponent nano-heterostructure aimed at photocatalytic prodn. of hydrogen. The system is composed of a platinum-tipped cadmium sulfide rod with an embedded cadmium selenide seed. In such structures, holes are three-dimensionally confined to the cadmium selenide, whereas the delocalized electrons are transferred to the metal tip. Consequently, the electrons are now sepd. from the holes over three different components and by a tunable phys. length. The seeded rod metal tip samples studied here facilitate efficient long-lasting charge carrier sepn. and minimize back reaction of intermediates. By tuning the nanorod heterostructure length and the seed size, the authors were able to significantly increase the activity for hydrogen prodn. compared to that of unseeded rods. This structure is highly active for hydrogen prodn., with an apparent quantum yield of 20% at 450 nm, and was active under orange light illumination and demonstrated improved stability compared to CdS rods without a CdSe seed.
- 5Venkatesan, M.; Fitzgerald, C. B.; Coey, J. M. D. Thin Films: Unexpected Magnetism in a Dielectric Oxide Nature 2004, 430, 630– 630 DOI: 10.1038/430630a5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXmt1Gis70%253D&md5=ac3e7a61621c2b09f4198e96084fe467Thin films: Unexpected magnetism in a dielectric oxideVenkatesan, M.; Fitzgerald, C. B.; Coey, J. M. D.Nature (London, United Kingdom) (2004), 430 (7000), 630CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Thin films of hafnium dioxide. (HfO2), an insulating oxide better known as a dielec. layer for nanoscale electronic devices, can be ferromagnetic even without doping. This discovery challenges the understanding of magnetism in insulators, because neither Hf4+ nor 02-are magnetic ions and the d and f shells of the Hf4+ ion are either empty or full. The reason for HFO2 being ferromagnetic is being analyzed in terms of the behavior of spin polarized electrons.
- 6Hong, N. H.; Sakai, J.; Poirot, N.; Brizé, V. Room-Temperature Ferromagnetism Observed in Undoped Semiconducting And Insulating Oxide Thin Films Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 132404 DOI: 10.1103/PhysRevB.73.1324046https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xkt12jsLk%253D&md5=bb9cf3a32cafed461bc527d3548c4633Room-temperature ferromagnetism observed in undoped semiconducting and insulating oxide thin filmsHong, Nguyen Hoa; Sakai, Joe; Poirot, Nathalie; Brize, VirginiePhysical Review B: Condensed Matter and Materials Physics (2006), 73 (13), 132404/1-132404/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Remarkable room-temp. ferromagnetism was obsd. in undoped TiO2, HfO2, and In2O3 thin films. The magnetic moment is rather modest in the case of In2O3 films on MgO substrates (while on Al2O3 substrates, it is neg. showing diamagnetism) when the magnetic field was applied parallel to the film plane. In contrast, it is very large in the other two cases (∼20 and 30 emu/cm3 for 200-nm-thick TiO2 and HfO2 films, resp.). Since bulk TiO2, HfO2, and In2O3 are clearly diamagnetic, and also, there are no contaminations in any substrate, the authors must assume that the thin film form, which might create necessary defects or oxygen vacancies, would be the reason for undoped semiconducting or insulating oxides to become ferromagnetic at room temp.
- 7Khalid, M.; Ziese, M.; Setzer, A.; Esquinazi, P.; Lorenz, M.; Hochmuth, H.; Grundmann, M.; Spemann, D.; Butz, T.; Brauer, G. Defect-Induced Magnetic Order in Pure ZnO Films Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 035331 DOI: 10.1103/PhysRevB.80.035331There is no corresponding record for this reference.
- 8Podila, R.; Queen, W.; Nath, A.; Arantes, J. T.; Schoenhalz, A. L.; Fazzio, A.; Dalpian, G. M.; He, J.; Hwu, S. J.; Skove, M. J. Origin of FM Ordering in Pristine Micro- and Nanostructured ZnO Nano Lett. 2010, 10, 1383– 1386 DOI: 10.1021/nl1001444There is no corresponding record for this reference.
- 9Arizumi, T.; Mizutani, T.; Shimakawa, K. EPR Study on Surface Properties of ZnS and CdS Jpn. J. of Appl. Phys. 1969, 8, 1411 DOI: 10.1143/JJAP.8.14119https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXmtFWquw%253D%253D&md5=c9b563ae5f788b047589bec0d9e96d3fE.P.R. study on surface properties of zinc sulfide and cadmium sulfideArizumi, Tetsuya; Mizutani, Teruyoshi; Shimakawa, KoichiJapanese Journal of Applied Physics (1969), 8 (12), 1411-16CODEN: JJAPA5; ISSN:0021-4922.The narrow EPR signals originated from the centers near the surface were observed in ZnS and CdS. These signals, appearing when heating the crushed samples in vacuum, have the same g values of 2.0027 ± 0.0003. Upon exposure to O, the signal height decreases with broadening in the line width through the dipolar interaction of O mols. adsorbed phys. onto the surface with the paramagnetic centers. At low temps., the signal becomes more sensitive to O and adsorbed water vapor prevents the dipolar interaction of O. The exptl. results suggest that the origin of the center is the S vacancy produced during the vacuum heat treatment.
- 10Madhu, C.; Sundaresan, A.; Rao, C. N. R. Room-Temperature Ferromagnetism in Undoped GaN And CdS Semiconductor Nanoparticles Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 201306 DOI: 10.1103/PhysRevB.77.201306There is no corresponding record for this reference.
- 11Coey, J. ferromagnetism Solid State Sci. 2005, 7, 660– 667 DOI: 10.1016/j.solidstatesciences.2004.11.01211https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXkvFKqsrs%253D&md5=050301d5c18e0e1a9cb099d1496bf221d0 ferromagnetismCoey, J. M. D.Solid State Sciences (2005), 7 (6), 660-667CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier B.V.)A review. Results on 4 ferromagnetic systems which contradict the accepted paradigms of localized or band magnetism are reviewed. The systems: irradiated graphite, nonstoichiometric CaB6, thin films of HfO2, and doped nonmagnetic oxides, all have small ferromagnetic moments and Curie points well above room temp. despite the absence of atoms with partially filled d or f shells. Parasitic ferromagnetic impurity phases are not a general explanation. A common feature is the presence of lattice or bond defects, which can give rise to an impurity band. Some of the ways in which this impurity band may become spin-polarized are discussed.
A tribute to Erwin Felix Bertaut.
- 12Khalid, M.; Setzer, A.; Ziese, M.; Esquinazi, P.; Spemann, D.; Pöppl, A.; Goering, E. Ubiquity of Ferromagnetic Signals in Common Diamagnetic Oxide Crystals Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 214414 DOI: 10.1103/PhysRevB.81.214414There is no corresponding record for this reference.
- 13Das Pemmaraju, C.; Sanvito, S. Ferromagnetism Driven by Intrinsic Point Defects in HfO2 Phys. Rev. Lett. 2005, 94, 217205 DOI: 10.1103/PhysRevLett.94.21720513https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXkvVChtLo%253D&md5=bedde517338dd38df5e0284f24cdab92Ferromagnetism Driven by Intrinsic Point Defects in HfO2Das Pemmaraju, Chaitanya; Sanvito, S.Physical Review Letters (2005), 94 (21), 217205/1-217205/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)In view of recent exptl. reports of unexpected ferromagnetism in HfO2 thin films, the authors carried out 1st-principles studies looking for magnetic order possibly brought about by the presence of small concns. of intrinsic point defects. Ab initio electronic structure calcns. using d. functional theory show that isolated cation vacancy sites in HfO2 give high-spin defect states. Also these appear to be ferromagnetically coupled with a rather short range magnetic interaction, resulting in a ferromagnetic ground state for the whole system. More interestingly, the occurrence of these high-spin states and ferromagnetism is in the low symmetry monoclinic phase of HfO2. This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.
- 14Osorio-Guillén, J.; Lany, S.; Barabash, S. V.; Zunger, A. Magnetism without Magnetic Ions: Percolation, Exchange, and Formation Energies of Magnetism-Promoting Intrinsic Defects in CaO Phys. Rev. Lett. 2006, 96, 107203 DOI: 10.1103/PhysRevLett.96.10720314https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xis1Sksb4%253D&md5=ae069f31e9a7ad2a8707ef7b4e29845eMagnetism without Magnetic Ions: Percolation, Exchange, and Formation Energies of Magnetism-Promoting Intrinsic Defects in CaOOsorio-Guillen, J.; Lany, S.; Barabash, S. V.; Zunger, A.Physical Review Letters (2006), 96 (10), 107203/1-107203/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We investigate theor. the prospects of ferromagnetism being induced by cation vacancies in nonmagnetic oxides. A single Ca vacancy V0Ca has a magnetic moment due to its open-shell structure but the ferromagnetic interaction between two vacancies extends only to four neighbors or less. To achieve magnetic percolation on a fcc lattice with such an interaction range one needs a min. of 4.9% vacancies, or a concn. 1.8×1021 cm-3. Total-energy calcns. for CaO show, however, that due to the high vacancy formation energy even under the most favorable growth conditions one can not obtain more than 0.003% or 1018 cm-3 vacancies at equil., showing that a nonequil. vacancy-enhancement factor of 103 is needed to achieve magnetism in such systems.
- 15Dev, P.; Zhang, P. Unconventional Magnetism in Semiconductors: Role of Localized Acceptor States Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 085207 DOI: 10.1103/PhysRevB.81.085207There is no corresponding record for this reference.
- 16Volnianska, O.; Boguslawski, P. High-Spin States of Cation Vacancies In GaP, GaN, AlN, BN, ZnO, and BeO: A First-Principles Study Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 205205 DOI: 10.1103/PhysRevB.83.20520516https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotVyksLw%253D&md5=3e984f44588f53c69646a354d76f0580High-spin states of cation vacancies in GaP, GaN, AlN, BN, ZnO, and BeO: A first-principles studyVolnianska, O.; Boguslawski, P.Physical Review B: Condensed Matter and Materials Physics (2011), 83 (20), 205205/1-205205/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)High-spin states of cation vacancies in GaP, GaN, AlN, BN, ZnO, and BeO were analyzed by first-principles calcns. The spin-polarized vacancy-induced level is located in the band gap in GaP, ZnO, and BeO. In the nitrides, the stronger exchange coupling forces the vacancy states to be resonant with valence bands, forbids formation of pos. charged vacancies in GaN and BN, and allows Al vacancy in p-AlN to assume the highest possible S = 2 spin state. The shape of the spin d., isotropic in the zinc-blende structure, has a pronounced directional character in the wurtzite structure. Stability of spin polarization of the vacancy states is detd. by spin-polarization energies of anions as well as by interat. distances between the vacancy neighbors and, thus, is given by both the lattice const. of the host and the at. relaxations around the vacancy. Implications for the expt. are discussed.
- 17Wang, X.; Zhao, M.; He, T.; Wang, Z.; Liu, X. Can Cation Vacancy Defects Induce Room Temperature Ferromagnetism In GaN Appl. Phys. Lett. 2013, 102, 062411 DOI: 10.1063/1.4792528There is no corresponding record for this reference.
- 18Shepidchenko, A.; Sanyal, B.; Klintenberg, M.; Mirbt, S. Small Hole Polaron In CdTe: Cd-Vacancy Revisited Sci. Rep. 2015, 5, 14509 DOI: 10.1038/srep1450918https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFOktb7K&md5=2c9fbcb3dd7a23050bb2eef5602f1942Small hole polaron in CdTe: Cd-vacancy revisitedShepidchenko, A.; Sanyal, B.; Klintenberg, M.; Mirbt, S.Scientific Reports (2015), 5 (), 14509CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)The characteristics of electronic states of Cd-vacancies in CdTe, an important semiconductor for various technol. applications, are under debate both from theor. and exptl. points of view. Exptl., the Cd-vacancy in its neg. charge state is found to have C3v symmetry and a (-1/-2) transition level at 0.4 eV. Our first principles d. functional calcns. with hybrid functionals confirm for the first time these exptl. findings. Addnl., we find that the C3v symmetry and the position of the (-1/-2) transition level are caused by the formation of a hole polaron localized at an anionic site around the vacancy.
- 19Chan, J. A.; Lany, S.; Zunger, A. Electronic Correlation in Anion p-orbitals Impedes Ferromagnetism Due To Cation Vacancies in Zn Chalcogenides Phys. Rev. Lett. 2009, 103, 016404 DOI: 10.1103/PhysRevLett.103.016404There is no corresponding record for this reference.
- 20Droghetti, A.; Pemmaraju, C. D.; Sanvito, S. Predicting d0 Magnetism: Self-Interaction Correction Scheme Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 78, 140404 DOI: 10.1103/PhysRevB.78.140404There is no corresponding record for this reference.
- 21Tang, J.-P.; Wang, L.; Luo, H.-J.; Xiao, W.-Z. Magnetic Properties in Zinc-Blende CdS Induced by Cd Vacancies Phys. Lett. A 2013, 377, 572– 576 DOI: 10.1016/j.physleta.2012.12.03821https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXltlKgsA%253D%253D&md5=6da27b391dfae001bd4fde9fbecf8fc6Magnetic properties in zinc-blende CdS induced by Cd vacanciesTang, Jian-Ping; Wang, Ling-ling; Luo, Hai-Jun; Xiao, Wen-ZhiPhysics Letters A (2013), 377 (7), 572-576CODEN: PYLAAG; ISSN:0375-9601. (Elsevier B.V.)The magnetic property induced by neutral Cd and S vacancies in CdS bulk and thin film were investigated, using 1st-principles simulation. For bulk CdS, the magnetism originates from Cd, instead of S, vacancies. The ferromagnetism with a Curie temp. above room temp. can be expected. For CdS thin film, both Cd and S vacancies does not yield any magnetism at the (111) surface, while local magnetic moments at the outermost S plane of the (001) surface is ascribed to the surface effect. The ferromagnetism at S-terminated (001) surface can account for the exptl. observation.
- 22Fischer, G.; Sanchez, N.; Adeagbo, W.; Szotek, Z.; Temmerman, W. M.; Ernst, A.; Hoffmann, M.; Hergert, W.; Muñoz, M. C. Ab Initio Study of the p-Hole Magnetism at Polar Surfaces of ZnO: The Role of Correlations J. Phys.: Condens. Matter 2016, 28, 016003 DOI: 10.1088/0953-8984/28/1/016003There is no corresponding record for this reference.
- 23Coey, M.; Ackland, K.; Venkatesan, M.; Sen, S. Collective Magnetic Response of CeO2 Nanoparticles Nat. Phys. 2016, 12, 694– 699 DOI: 10.1038/nphys367623https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjsFenu7Y%253D&md5=022b24899431fcb3d0e095ba8801270dCollective magnetic response of CeO2 nanoparticlesCoey, Michael; Ackland, Karl; Venkatesan, Munuswamy; Sen, SiddharthaNature Physics (2016), 12 (7), 694-699CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)The magnetism of nanoparticles and thin films of wide-bandgap oxides that include no magnetic cations is an unsolved puzzle. Progress has been hampered by both the irreproducibility of much of the exptl. data, and the lack of any generally accepted theor. explanation. The characteristic signature is a virtually anhysteretic, temp.-independent magnetization curve that sats. in an applied field that is several orders of magnitude greater than the magnetization. It would seem as if a tiny vol. fraction, .ltorsim.0.1%, of the samples is magnetic and that the energy scale is unusually high for spin magnetism. Here we investigate the effect of dispersing 4 nm CeO2 nanoparticles with powders of γAl2O3, sugar or latex microspheres. The satn. magnetization, Ms ≈ 60 A m-1 for compact samples, is maximized by 1 wt% lanthanum doping. Dispersing the CeO2 nanopowder reduces its magnetic moment by up to an order of magnitude, and there is a characteristic length scale of order 100 nm for the magnetism to appear in CeO2 nanoparticle clusters. The phenomenon is explained in terms of a giant orbital paramagnetism that appears in coherent mesoscopic domains due to resonant interaction with zero-point fluctuations of the vacuum electromagnetic field. The theory explains the obsd. temp.-independent magnetization curve and its doping and dispersion dependence, based on a length scale of 300 nm that corresponds to the wavelength of a max. in the UV absorption spectrum of the magnetic CeO2 nanoparticles. The coherent domains occupy roughly 10% of the sample vol.
- 24Kaewmaraya, T.; Pathak, B.; Araujo, C. M.; Rosa, A. L.; Ahuja, R. Water Adsorption on ZnO(1010): The Role of Intrinsic Defects Europhys. Lett. 2012, 97, 17014 DOI: 10.1209/0295-5075/97/17014There is no corresponding record for this reference.
- 25Giacopetti, L.; Satta, A. Degradation of Cd-Yellow Paints: Ab Initio Study Of Native Defects in 10.0 Surface CdS Microchem. J. 2016, 126, 214– 219 DOI: 10.1016/j.microc.2015.12.00525https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVKrtb3N&md5=322da49ea235c8e0f78bac00ecc6d129Degradation of Cd-yellow paints: Ab initio study of native defects in {10.0} surface CdSGiacopetti, Laura; Satta, AlessandraMicrochemical Journal (2016), 126 (), 214-219CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)Relevant effects produced at the surface of modern paintings include the growth of discolored crusts. In the specific case of cadmium yellow paints (CdS), white globular compds. mostly formed by hydrated cadmium sulfate and cadmium carbonate are obsd. The origins of such chem. and phys. alterations are still under debate. Structural defects in CdS, among other possible causes like photo-oxidn. processes, may play a role in the degrdn. process. Their presence in the pigment surface alters the electronic structure of cadmium sulfide by forming acceptor levels in the gap of the semiconductor. Such levels make the surface more reactive in the interaction with external agents (oxygen, water...). To this end, we present a theor. study of point defects, namely Cd- and S-vacancies, in the {10.0} CdS surface. The geometrical and electronic structures as well as the vacancy formation energies are detd. with the use of a first method. All the calcns. are performed within the framework of the d. functional theory (DFT) in the Generalized Gradient Approxn. (GGA-PBE) with the use of ultrasoft pseudopotentials.
- 26Giacopetti, L.; Satta, A. Degradation of Cd-Yellow Paints: Ab Initio Study of the Adsorption of Oxygen and Water on 10.0 CdS Surface J. Phys.: Conf. Ser. 2014, 566, 012021 DOI: 10.1088/1742-6596/566/1/012021There is no corresponding record for this reference.
- 27Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects Phys. Rev. 1965, 140, A1133– A1138 DOI: 10.1103/PhysRev.140.A1133There is no corresponding record for this reference.
- 28Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations For Metals and Semiconductors Using a Plane-Wave Basis Set Comput. Mater. Sci. 1996, 6, 15– 50 DOI: 10.1016/0927-0256(96)00008-028https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmtFWgsrk%253D&md5=779b9a71bbd32904f968e39f39946190Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis setKresse, G.; Furthmuller, J.Computational Materials Science (1996), 6 (1), 15-50CODEN: CMMSEM; ISSN:0927-0256. (Elsevier)The authors present a detailed description and comparison of algorithms for performing ab-initio quantum-mech. calcns. using pseudopotentials and a plane-wave basis set. The authors will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temp. d.-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N2atoms scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge d. including a new special preconditioning optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. The authors have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio mol.-dynamics package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
- 29Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169– 11186 DOI: 10.1103/PhysRevB.54.1116929https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xms1Whu7Y%253D&md5=9c8f6f298fe5ffe37c2589d3f970a697Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis setKresse, G.; Furthmueller, J.Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
- 30Nishidate, K.; Sato, T.; Matsukura, Y.; Baba, M.; Hasegawa, M.; Sasaki, T. Density-Functional Electronic Structure Calculations for Native Defects and Cu Impurities in CdS Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 035210 DOI: 10.1103/PhysRevB.74.03521030https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XotFWhu7s%253D&md5=2a6e06fdec795e001735a45a89d1f26dDensity-functional electronic structure calculations for native defects and Cu impurities in CdSNishidate, Kazume; Sato, Takuya; Matsukura, Yuta; Baba, Mamoru; Hasegawa, Masayuki; Sasaki, TaizoPhysical Review B: Condensed Matter and Materials Physics (2006), 74 (3), 035210/1-035210/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We performed d.-functional electronic structure calcns. for wurtzite CdS with native defects and Cu impurity. We investigate formation energies and ionization levels of the defects in various charge states. Our results reveal that the S vacancy is a double donor with the strongly localized orbital at the defect site, and could act as an intrinsic compensation defect under p-type doping. On the other hand, the interstitial S at the tetrahedral site is a double acceptor which forms into a dumbbell-like at. configuration with the nearest S atom. The impurity Cu substituting Cd produces a single acceptor state, while the interstitial Cu generates a single donor state. The calcd. formation energies imply that the donor state could also cause the compensation in the Cu doped CdS.
- 31Adachi, S. Properties of Group-IV, III-V and II-VI Semiconductors; John Wiley & Sons, Ltd.: New York, 2005; pp 1– 21.There is no corresponding record for this reference.
- 32Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple Phys. Rev. Lett. 1996, 77, 3865– 3868 DOI: 10.1103/PhysRevLett.77.386532https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630Generalized gradient approximation made simplePerdew, John P.; Burke, Kieron; Ernzerhof, MatthiasPhysical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
- 33Klimes, J.; Bowler, D. R.; Michaelides, A. Chemical Accuracy for the Van Der Waals Density Functional J. Phys.: Condens. Matter 2010, 22, 022201 DOI: 10.1088/0953-8984/22/2/02220133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXitFKitb8%253D&md5=37cca57a611ebd2fea99edd70d979091Chemical accuracy for the van der Waals density functionalKlimes, Jiri; Bowler, David R.; Michaelides, AngelosJournal 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.
- 34Klimes, J.; Bowler, D. R.; Michaelides, A. Van der Waals Density Functionals Applied to Solids Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 195131 DOI: 10.1103/PhysRevB.83.19513134https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotVOlsbY%253D&md5=0e3350e5db3aa6fee4eadea9c6582255Van der Waals density functionals applied to solidsKlimes, Jiri; Bowler, David R.; Michaelides, AngelosPhysical 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.
- 35Wei, S.-H.; Zunger, A. Role of Metal D States in II-VI Semiconductors Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 8958– 8981 DOI: 10.1103/PhysRevB.37.895835https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXkvVSjsrk%253D&md5=4a52c17c7dabbdc3b5fe4eb181336e72Role of metal d states in II-VI semiconductorsWei, S. H.; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (1988), 37 (15), 8958-81CODEN: PRBMDO; ISSN:0163-1829.All-electron band-structure calcns. and photoemission expts. on II-VI semiconductors both exhibit a metal d subband inside the main valence band. It has nevertheless been customary in pseudopotential and tight-binding approaches to neglect the metal d band by choosing Hamiltonian parameters which place this band inside the chem. inert at. cores. By using all-electron self-consistent electronic-structure techniques (which treat the outermost d electrons in the same way as other valence electrons) and by comparing the results to those obtained by methods which remove the d band from the valence spectrum, the effects on valence properties were studied. For II-VI semiconductors p-d repulsion and hybridization (1) lower the band gaps, (2) reduce the cohesive energy, (3) increase the equil. lattice parameters, (4) reduce the spin-orbit splitting, (5) alter the sign of the crystal-field splitting, (6) increase the valence-band offset between common-anion II-VI semiconductors, and (7) modify the charge distributions of various II-VI systems and their alloys. P-d repulsion is also responsible for the occurrence of deep Cu acceptor levels in II-VI semiconductors (compared with shallow acceptors of Zn in III-V), for the anomalously small band gaps in chalcopyrites, and for the neg. exchange splitting in ferromagnetic MnTe.
- 36Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P. Electron-Energy-Loss Spectra and the Structural Stability of Nickel Oxide: An LSDA+U Study Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 57, 1505– 1509 DOI: 10.1103/PhysRevB.57.150536https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXlsVarsQ%253D%253D&md5=9b4f0473346679cb1a8dce0ad7583153Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA+U studyDudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P.Physical Review B: Condensed Matter and Materials Physics (1998), 57 (3), 1505-1509CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)By taking better account of electron correlations in the 3d shell of metal ions in Ni oxide it is possible to improve the description of both electron energy loss spectra and parameters characterizing the structural stability of the material compared with local spin d. functional theory.
- 37Vesely, C. J.; Hengehold, R. L.; Langer, D. W. Uv Photoemission Measurements of the Upper D Levels in the IIB-VIA Compounds Phys. Rev. B 1972, 5, 2296– 2301 DOI: 10.1103/PhysRevB.5.2296There is no corresponding record for this reference.
- 38Monkhorst, H. J.; Pack, J. D. Special Points For Brillouin-Zone Integrations Phys. Rev. B 1976, 13, 5188– 5192 DOI: 10.1103/PhysRevB.13.5188There is no corresponding record for this reference.
- 39Lany, S. Semiconductor Thermochemistry in Density Functional Calculations Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 78, 245207 DOI: 10.1103/PhysRevB.78.24520739https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXitlWmuw%253D%253D&md5=64766d7d38bd31f6986b9b20bc0a5637Semiconductor thermochemistry in density functional calculationsLany, StephanPhysical Review B: Condensed Matter and Materials Physics (2008), 78 (24), 245207/1-245207/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The local-d. and generalized gradient approxns. (LDA and GGA) to d. functional theory (DFT) exhibit incomplete error cancellation when energy differences are taken between chem. dissimilar systems. This energy inconsistency is manifested, e.g., in the tendency to underestimate the heat (enthalpy) of formation of semiconducting and insulating compds. in LDA and, even more so, in GGA. Considering a set of 61 compds. that can be formed from 14 elements (cations: Cu, Mg, Ca, Zn, Cd, Al, Ga, and In; anions: N, P, As, O, S, and Se), optimized elemental ref. energies are detd. by least-squares error minimization of an overdetd. set of linear equations. These elemental energies are "optimally consistent" with the DFT energies of the semiconductor compds. and imply corrections of up to 1 eV compared to the resp. LDA or GGA energies. While these "corrections" are not to be understood to yield the correct abs. total energies of the elements, they are proposed to give appropriate bounds for the chem. potentials for thermodn. processes in semiconductors and insulators, such as, e.g., defect formation, surface reconstruction, or catalytic processes. The present model allows to evaluate thermodn. processes using DFT energy differences taken only between systems that are expected to show good error cancellation.
- 40Implementation of Van der Waals Density Functional Approach to the Spin-Polarized System: Interaction Potential between Oxygen Molecules. J. Phys. Soc. Jpn. 2013, 82, 093701.There is no corresponding record for this reference.
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(I) Local DOS of S atoms neighboring the VCd in bulk CdS (PDF)
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