ASAP (As Soon As Publishable)

Gas-phase reaction of ozone and hydrogen peroxide to form water and singlet oxygen, a reactive oxygen species, has been investigated employing density functional theory and ab initio coupled cluster, CCSD(T) methods. The calculated H₂O₂ loss (4.01 × 10^–7 s^–1 at 296 K) has excellent agreement with the experimental observations considering the ozone concentration in the stratosphere and upper troposphere of the order of 10¹³ molecules cm^–3. Notably, a new pathway leading to the formation of H₂O₅ has been observed, which has not been reported in the existing literature until now.

The force-balance equation of time-dependent density-functional theory presents a promising route toward obtaining approximate functionals; however, so far, no practical correlation functionals have been derived this way. In this work, starting from a correlated wave function proposed originally by Colle and Salvetti [Theoret. Chim. Acta 37, 329 (1975)], we derive an analytical correlation-energy functional for the ground state based on the force-balance equation. The new functional is compared to the local-density correlation of the homogeneous electron gas, and we find an increased performance for atomic systems, while it performs slightly worse on solids. From this point onward, the new force-based correlation functional can be systematically improved.

Accurate prediction of thermodynamic properties of mixtures, such as activity coefficients, is essential for designing and optimizing chemical processes. While established physics-based methods face limitations in prediction accuracy and scope, emerging machine learning approaches, such as matrix completion methods (MCMs), offer promising alternatives. However, their performance can suffer in data-sparse regions. To address this issue, we propose a novel hybrid MCM for predicting activity coefficients at infinite dilution at 298 K that not only uses experimental training data but also includes synthetic training data from two sources: predictions obtained from the physics-based modified UNIFAC (Dortmund) and from a similarity-based approach developed in previous work. The resulting hybrid method combines the broad applicability of MCMs with the precision of the similarity-based approach, resulting in a more robust prediction framework that excels even in regions with limited data. Additionally, our analysis provides valuable insights into how different types of training data affect the prediction accuracy. When experimental data are sparse, incorporating synthetic training data from modified UNIFAC (Dortmund) and the similarity-based approach significantly improves the performance of the MCMs. Conversely, even with abundant experimental data, high accuracy is achieved only if the training set includes mixtures similar to those of interest.

An approach for obtaining high-level ab initio potential surfaces is described. The approach takes advantage of machine learning strategies in a two-step process. In the first, the molecular-orbital based machine learning (MOB-ML) model uses Gaussian process regression to learn the correlation energy at the CCSD(T) level using the molecular orbitals obtained from Hartree–Fock calculations. In this work, the MOB-ML approach is expanded to use orbitals obtained using a smaller basis set, aug-cc-pVDZ, as features for learning the correlation energies at the complete basis set (CBS) limit. This approach is combined with the development of a neural-network potential, where the sampled geometries and energies that provide the training data for the potential are obtained using a diffusion Monte Carlo (DMC) calculation, which was run using the MOB-ML model. Protocols are developed to make full use of the structures that are obtained from the DMC calculation in the training process. These approaches are used to develop potentials for OH^–(H₂O) and H₃O⁺(H₂O), which are used for subsequent DMC calculations. The results of these calculations are compared to those performed using previously reported potentials. Overall, the results of the two sets of DMC calculations are in good agreement for these very floppy molecules. Potentials are also developed for OH^–(H₂O)₂ and OH^–(H₂O)₃, for which there are not available potential surfaces. The results of DMC calculations for these ions are compared to those for the corresponding H₃O⁺(H₂O)₂ and H₃O⁺(H₂O)₃ ions. It is found that the level of delocalization of the shared proton is similar for a hydroxide or hydronium ion bound to the same number of water molecules. This finding is consistent with the experimental observation that these sets of ions have similar spectra.

The possibility of stabilizing reactive dimethylzinc through salt formation has been investigated using advanced ab initio electronic structure methods and flexible basis sets. It was found that the attachment of a Cl^– ion to dimethylzinc is thermodynamically favorable (with a Gibbs free reaction energy of −22.88 kcal/mol at room temperature), occurring without a kinetic barrier. The resulting anion is strongly electronically bound, with an excess electron binding energy of 4.306 eV. The subsequent attachment of Li⁺ or Na⁺ ions to this anion leads to the formation of ionic salts (CH₃)₂ZnClLi or (CH₃)₂ZnClNa. These salts, formed through this two-step process, are thermodynamically stable and represent stabilized forms of dimethylzinc, from which the pure dimethylzinc compound can be regenerated via the procedures suggested in this work. In addition to the structural characterization of these systems and a detailed analysis of the electronic structure of the (CH₃)₂ZnCl^– anion, which plays a key role in the described process, experimental approaches for realizing each transformation are also proposed.

Aliphatic hydroxyamino acids, namely, α-hydroxyglycine, α-hydroxyalanine, serine, threonine, and homoserine, were studied by quantum chemical calculations using two methods in water as a solvent. A hybrid variant of DFT–B3LYP was applied to optimize the geometry of neutral molecules, molecular cations, and anions for the canonical and zwitterionic form of amino acids. In the energy minimum, vibrational analysis was applied, enabling the evaluation of thermodynamic functions (internal energy, enthalpy, entropy, and Gibbs energy) of individual species and absolute oxidation and reduction potentials for redox couples. In the B3LYP preoptimized geometry, the advanced DLPNO–CCSD(T) method was applied to include the major part of the interelectron correlation energy. Calculated molecular descriptors were compared with previously studied molecules by the same method, and the whole set for 17 amino acids was processed by advanced statistical methods such as cluster analysis and principal component analysis. Calculated oxidation potentials correlate with the adiabatic ionization energies along a straight line, and analogously, the calculated reduction potential correlates with the electrophilicity index. The ionization energy in α-amino acids is systematically influenced (reduced) by the functional groups such as hydroxyl, methyl, ethyl, and iso-propyl; it decreases along a series of α-, β-, γ-, and δ-amino acids.

HO₂^• is a crucial radical in atmospheric chemistry, with applications ranging from HO₂^•/OH^• interconversion to controlling the budget of various trace gases in the atmosphere. It is known that one of the potential sinks for HO₂^• is clouds and aerosols, though the mechanism is not clear to date. In the present study, using Born–Oppenheimer molecular dynamics simulations, we have demonstrated that the dissociation of HO₂^• on the surface of a water droplet, as well as in the bulk phase, is a spontaneous process. In addition, we have computed the Gibbs free energy for the deprotonation of HO₂^• on both the surface and in the bulk, which suggests that deprotonation of HO₂^• on the surface occurs faster compared to the same in the bulk.

The structures, isomerization energies, and rotational and vibrational spectra of prototypical CN-substituted polycyclic hydrocarbons in the gas phase have been analyzed using a general computational strategy based on Pisa composite schemes (PCS) and second-order vibrational perturbation theory (VPT2). The final results obtained in this way show, in most cases, relative average deviations with respect to experimental rotational constants close to 0.1%, corresponding to errors of around 1 mÅ and 0.1° for bond lengths and valence angles, respectively. At the same time, fundamental IR absorption bands are reproduced with average deviations below 10 cm^–1 without any scaling factor. In addition to the intrinsic interest of the studied molecules, this work confirms that spectroscopic studies of large systems can be supported by unsupervised computational tools that couple accuracy with reasonable cost.

A novel parameterization of a self-consistent charge density functional-based tight-binding scheme (SCC-DFTB) to characterize gold (Au)-water hybrid systems by developing new pair parameters for (Au, O, H-X where X = Au, O, H) using the DFTB module of Material Studio 2020 is introduced. To characterize Au-water systems within the DFTB framework, the derived parameters are systematically compared with DFT-DMOL3 and DFTB-AuOrg (existing library of DFTB) data for Au_n clusters (n = 2, 4, 8, 25, and 34), Au_n mono layer surfaces (n = 7, 19, 25, 37, and 49), Au₅₀ bilayer surface, and Au nanostructures-H₂O complexes. The geometrical, energetic, and electronic characteristics derived from the newly parametrized library (DFTB-AuOH) for the Au clusters align well with both the DFT-DMOL3 and the DFTB-AuOrg results, demonstrating that the stability of the Au clusters is accurately represented by the existing parameters. The structural outcomes derived from the DFTB-AuOH for Au surfaces indicate its substantial capability to optimize extensive gold surfaces in comparison to the DFT-DMOL3 approach, in which, in this case, the DFTB-AuOrg approach identified bent surfaces as the optimized configurations. Furthermore, the structural and energetic achievements determined from the DFTB-AuOH for Au nanostructure complexes with water molecule(s) reveal low-energy configurations and optimized structures with minimal variation when compared to DFT-DMOL3. The linear correlation equations of Y = (−0.044) X – 10.198 and Y = (−0.05) X – 10.538 are applied to the adsorption and interaction energy, respectively, to scale these DFTB-AuOH energies to their corresponding DFT-DMOL3 energies and to investigate all these energies in relation to the gold surface size, thereby confirming these accomplishments and demonstrating their compatibility significantly. The activation energy of water dissociation on Au surfaces is compared through all three approaches, and it also demonstrates significant compatibility as well. Lastly, the study of the molecular dynamics simulations reveals significant variations in the expected dynamic behavior among the DFTB-AuOH, DFT-DMOL3, and DFTB-AuOrg techniques. DFTB-AuOH consistently exhibits variations that more closely align with DFT-DMOL3, albeit of lesser magnitude, in contrast to DFTB-AuOrg, which predicts significantly smaller fluctuations overall.

Furfural is a typical representative molecule of furan compounds and an important intermediate species in the oxidation of furan derivatives. The rate constant of furfural with OH is calculated for the first time using a high-level quantum chemistry method combined with the Rice–Ramsperger–Kassel–Marcus theory/master equation method. The M06-2X/jun-cc-pVTZ method was used to construct the potential energy surface of the reaction path. The preliminary reactions can occur through three different pathways: H-abstraction from the furan ring, H-abstraction from the side chain, and a preliminary OH-addition. The pathways via the OH-addition mechanism of the furfural + OH system were superior to H-abstraction in the temperature range of 298–400 K. When the temperature exceeds 400 K, the H-abstraction will be faster. Moreover, with the increase of pressure, the competition of the pathway via the OH-addition mechanism in the low-temperature region will gradually weaken. Under low-temperature conditions, INT1 and INT4 are the main intermediate species. The formation of bimolecular products, the 2-furanol (P7) + aldehyde group and the (3E)-4-hydroxybuta-1,3-diene-1-one (P8) + aldehyde group at C(2) and C(5) sites, are the main reaction pathways via the OH-addition mechanism. The formation of (2-furanyl)(oxy) methyl (P4) + H₂O (i.e., R4) always dominates for the four H-abstraction reactions. For the initial H-abstraction reaction, there is no pressure dependence, but for the preliminary OH-addition reaction, there is a significant positive pressure dependence. This work not only provides the necessary rate constants for modeling development but also provides theoretical guidance for the practical application of furan-based fuel.

With the application of nonfullerene acceptors (NFAs) Y6 and its derivatives, the power conversion efficiencies (PCEs) of single-junction organic solar cells (OSCs) have exceeded 20%. Side-chain engineering has proven to be an important strategy for optimizing Y6-based NFAs. However, studies on the incorporation of conjugated side chains into Y6-based NFAs are still rare, and the corresponding underlying mechanisms are still not well understood. In this article, we systematically designed eight molecules based on modifications to the conjugated side chains of two reported Y6-based NFAs, involving alterations of branched alkyl chains at different positions on the thiophene, benzene, bithiophene, and benzene-thiophene moieties that serve as conjugated side chains. Using reliable density functional theory (DFT) and time-dependent DFT calculations, we obtained key photovoltaic parameters such as molecular planarity, dipole moments, electrostatic potential and corresponding fluctuations, frontier molecular orbitals, exciton binding energy (E_b), singlet–triplet energy differences (ΔE_ST), and UV–vis absorption spectra of these newly designed NFAs. The results show that the side conjugated rings and the positions of lateral alkyl chains attached to these rings exert noticeable influences on their photoelectric properties. Notably, compared to the prototype T3EH, 2T2EH, 2T3EH, PT2EH, PT3EH, and P2EH exhibit enhanced absorption (manifesting as increased total oscillator strength) and smaller E_b and ΔE_ST values, hinting at their promising potential as novel NFAs.

The formation of nitrogen- and sulfur-containing organic compounds (N-Org and S-Org) is important for atmospheric secondary organic aerosol (SOA) production, thereby influencing air quality and global climate. However, the mechanisms underlying N-Org and S-Org formation on aerosol particle surfaces are poorly understood due to the limited availability of surface-sensitive analytical techniques. This study investigates the surface interactions of glyoxal (GL), a known SOA precursor, with ammonium sulfate (NH₄)₂SO₄, under varying relative humidity (RH) conditions, using ambient-pressure X-ray photoelectron spectroscopy (APXPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and molecular dynamics (MD) simulations. N-Org species, such as imines, a key intermediate in brown carbon (BrC) formation, are identified on the (NH₄)₂SO₄ surface at low RH (≤13.3%). The formed S-Org species cannot be specified due to the difficulties in distinguishing S-Org from inorganic sulfate in the XPS spectra. Elemental ratios on (NH₄)₂SO₄ surface across the entire probing depth show increased S/O and N/O ratios upon GL exposure, indicating the formation of N-Org and S-Org species. NEXAFS measurements further confirm the surface changes of (NH₄)₂SO₄ associated with the adsorption of GL and water. These findings provide compelling evidence of surface-driven N-Org and S-Org formation pathways, demonstrating that heterogeneous reactions on (NH₄)₂SO₄ particle surfaces could be an active source of atmospheric BrC and SOA.

We report the first observation of triplet–singlet resonance energy transfer at room temperature without involving the intersystem crossing process. Triplet (T₁) to singlet (S₁) Förster resonance energy transfer (FRET) has been measured at room temperature with a long-wavelength direct donor’s triplet-state excitation. The donor coumarin 106 (C106D) and acceptor rhodamine 101 (R101A) were embedded in thin poly(vinyl alcohol) (PVA) films. The direct excitation of the C106D triplet state was at 470 nm, well outside the absorption, which avoids the donor singlet-state excitation and its involvement in the FRET process. The intensity of C106D decreases in the presence of R101 and is accompanied by an increase of acceptor R101A emission. The observed FRET results in a red glow of the illuminated area lasting hundreds of milliseconds. The FRET measurements with direct triplet-state excitation can also be used to estimate the photophysical parameters of the donor triplet state.

Identifying atomic-level mechanisms in elemental chemical reactions is crucial for understanding complex reaction processes. This study focuses on the typical multichannel H + NH₂Cl reaction, which plays a significant role in environmental science. High-level ab initio calculations determined seven distinct reaction pathways, leading to three product channels: H₂ + NHCl, HCl + NH₂, and Cl + NH₃. A full-dimensional, globally accurate potential energy surface was constructed by fitting 143,333 ab initio energy points, calculated at the UCCSD(T)-F12a/aug-cc-pVTZ level. The atomic-level mechanisms of the reaction along these seven pathways were identified and visualized using quasi-classical trajectory calculations. Interestingly, a novel reaction mechanism, termed “heavy-atom assisted rotation”, was discovered. In this light-heavy-heavy reaction, the attacked heavy atom (either Cl or N) acts as a “gangplank”, propelling the light H atom in front of the other heavy atom through rotational motion. This mechanism results in forward and sideward scattering of products at small impact parameters, which contrasts with any known direct mechanisms.

The hemibond, a nonclassical covalent bond involving three electrons shared between two centers, has attracted considerable attention due to its significance in radiation chemistry. Water radical cation clusters, [H₂O–X]⁺, exhibit two primary bonding motifs: the hemibond and the hydrogen bond. Although hydrogen bond formation typically dominates, recent studies have identified instances of hemibond formation in some systems involving water molecules. This study focuses on the [H₂O–N₂O]⁺ radical cation cluster, a rare system exhibiting hemibond formation. We investigate the stability of this hemibond in [H₂O–N₂O]⁺ against microhydration by employing infrared photodissociation spectroscopy and conducting theoretical calculations on [H₂O–N₂O]⁺-(H₂O)_n (n = 1 and 2). By comparing experimental and simulated spectra, we determined the predominant intermolecular bonding motifs in [H₂O–N₂O]⁺-(H₂O)_n (n = 1 and 2). Our analysis revealed that proton-transferred-type isomers are almost exclusively populated for n = 1 and 2, whereas hemibonded-type isomers are energetically unfavorable. These findings indicate that microhydration disrupts the hemibond and shifts the stable structural motifs.

Nitreones are compounds with the general formula L → N⁺ ← L′. These compounds exhibit medicinal properties and have found applications in phase transfer catalysis. A few nitreones are cyclic; protonated cycloguanil (an antimalarial agent) is the most prominent example. Recently, a few more cyclic compounds were experimentally reported, in which the central N⁺ was shown to exhibit nitreone character. This led to attention being paid to the chemistry of neutral cyclic nitreones. A thorough literature search led to two sets of cyclic nitreones: C → N ← C type and P → N ← P type. In this work, we report quantum chemical analysis in exploring the electronic structure of neutral cyclic nitreones. Molecular orbital analysis, electron density analysis, charge, electron localization function (ELF), complexation energy values, and Tolman electronic parameter (TEP) all indicate that the studied compounds do carry nitrogen in the N(I) oxidation state and the two lone pairs are at the central nitrogen; thus, they qualify to be considered as cyclic nitreones.

Global diabatic potential energy surfaces (PESs) of the H₂S⁺ system, corresponding to the 1⁴A″ and 2⁴A″ electronic states, were built by using the neural network method. In ab initio calculations, the aug-cc-pVTZ basis set and MRCI-F12 method were adopted. The topographic features of the new diabatic PESs were discussed and compared with the available theoretical and experimental results in detail. The spectroscopic parameters obtained from the diabatic PESs are in good agreement with previous theoretical and experimental results. Based on the newly constructed diabatic PESs, the nonadiabatic dynamics calculations of the S⁺ + H₂(v₀ = 2, j₀ = 0) → SH⁺ + H reaction were carried out using the time-dependent wave packet method. To further understand the nonadiabatic effect, the adiabatic dynamical calculations of the title reaction were also performed based on the adiabatic PES, which was obtained by diagonalizing the diabatic PESs. The deviation between nonadiabatic results and adiabatic values is very obvious. In general, the adiabatic results underestimate the dynamics result at low collision energies and overestimate the dynamics results within high collision energy ranges. Therefore, to obtain accurate dynamics results, the nonadiabatic effect should be included in the calculation.

Owing to the existence of surface defects, quantum dots (QDs) could be unstable, and thus, the design of proper ligands to improve their stability and optical performance is challenging. In this work, four D-π-A ligands were designed by modulating the D part of merocyanine and were grafted onto Cd₃₃Se₃₃ QD via a Cd–S bond, forming Cd₃₃Se₃₃@D-π-A complexes. It was found that a hole trap appeared between the HOMO and LUMO of the Cd₃₃Se₃₃@D-π-A complexes in vacuum, and the stronger the electron-donating capability of the D part, the higher the activation energy of the trap, which disappeared in solvent environments. The ligand-to-metal charge transfer (LMCT) mechanism of Cd₃₃Se₃₃@D-π-A complexes induced a fluorescence quenching phenomenon in vacuum, while in solution, the local excitation on the D-π-A ligand facilitated stronger fluorescence due to the enhanced electron-donating capability of its D part. The present study provides a strategy for improving the optical performance of functional QDs through the design and optimization of D-π-A ligands, shedding light on the development and applications of novel functional QDs.

Hydrogen selenide, H₂Se, is the third-row analog of hydrogen sulfide, H₂S, and water, H₂O. While there is ample thermochemical and kinetic information about the reactions of the latter two species, few experimental or theoretical data are available on H₂Se. In this work, we use high-level post-Hartree–Fock methods to study the reaction of H₂Se with two of the most abundant atmospheric radical species, the Cl^• atom and the ^•OH radical, H₂Se + Cl^• → HSe^• + HCl H₂Se + ^•OH → HSe^• + H₂O We used the SVECV-f12 composite quantum chemical method to study the stability of adducts and transition states, as well as the barriers for the transformations. It was found that a correct representation of the barrierless adduct is crucial for a correct description of the reaction’s kinetics, and we present in this paper the first theoretical determination of the reaction coefficient of H₂Se with Cl^• in the literature, obtaining a value of 5.7 × 10^–10 cm³ molecule^–1 s^–1, in excellent agreement with the experimental determination of 5.5 × 10^–10 cm³ molecule^–1 s^–1 at room temperature Additionally, using the same procedure, we obtained a value of 6.4 × 10^–11 cm³ molecule^–1 s^–1 for the reaction with ^•OH, in this case slightly smaller than the only previous estimation of 7.2 × 10^–11 cm³ molecule^–1 s^–1 obtained indirectly from similar reactions for sulfur compounds, in all cases at 298.15 K. Judging from the agreement of the theoretical and experimental rate coefficients in the case of the reaction with chlorine, we suggest that our value for the reaction with the hydroxyl radical is more accurate than the estimated one. A comparison of the dependence of the rate coefficients for H₂S and H₂Se as a function of the temperature shows some noticeable differences. A convex behavior of the T-dependence for the Cl^• reaction at high temperatures was found, instead of the concave behavior found for sulfur. Nevertheless, this is not important in atmospheric chemistry conditions, and a sufficiently linear region was found with the expression, k(Cl^•) = 1.6 × 10^–10 exp (0.7/RT) cm³ molecule^–1 s^–1. The reaction with ^•OH is even more complicated, with nonlinear tail at high (combustion) and low (stratosphere) temperatures, while the region important in tropospheric chemistry could be fitted with the Arrhenius equation k(^•OH) = 5.9 × 10^–12 exp (1.4/RT) cm³ molecule^–1 s^–1. Using our theoretically determined kinetic data, we were also able to calculate the atmospheric lifetime of H₂Se as 2.6 h, considerably shorter than that of H₂S (12.2 h).

Density functional approximations became indispensable tools in many fields of chemistry due to their excellent cost-to-accuracy ratio. Still, consideration is required to select an appropriate approximation for each task. Highly parameterized Minnesota functionals are known for their excellent accuracy in reproducing thermochemical properties and, in particular, weak medium-range interactions. Here, we show that the latter ability of many Minnesota functionals comes from exploiting the basis set incompleteness. This finding shows how empirical functionals can trick their makers by learning to operate in a physics-defying way and likely explains the previously observed tendency of Minnesota functionals to distort electron densities. Thus, satisfaction of the Hellmann–Feynman theorem should be considered an important test and parameterization goal for the future generations of highly parameterized density functionals, including those based on neural networks.

Approaches for evaluating excited state wave functions and energies using diffusion Monte Carlo (DMC) with guiding functions (guided DMC) are discussed. For this work, the guiding functions are functions of a subset of the 3N – 6 coordinates that are needed to describe the structure of the molecule of interest. The DMC wave functions are used to evaluate intensities using two approaches. In the trial wave function approach, the product of the molecular wave function for one of the states involved in the transition and the guiding function for the second state is used to evaluate the matrix elements of the dipole moment. In the descendant weighting approach, descendant weights are used to evaluate the value of the wave function for one of the states involved in the transition at the geometries sampled by the DMC wave function for the second state. The descendant weighting approximation is shown to be more accurate as well as computationally more expensive compared to approximations that are based on various forms of the trial wave function approach. Strategies are explored, which combine results of different forms of the trial wave function approximation to minimize the errors in this approach. The trial wave function and descendant weighting approaches are applied to a study of a harmonic oscillator, where the sensitivity of the calculated energies and intensities to the quality of the trial wave function is explored. The two approaches are also applied to calculations of frequencies and intensities of transitions in water, H₃O₂^–, a four-dimensional (4D) model based on H₃O₂^– and H₅O₂⁺. We also show how comparisons of the results obtained using several forms of the trial wave function approach allow us to explore how couplings among vibrational motions are reflected in the intensities.

Despite decades of work on aqueous lead (Pb) adsorption on α-Fe₂O₃ (hematite) and α-Al₂O₃ (alumina), gaps between measurements and modeling obscure molecular-level understanding. Achieving well-matched geometries between theory and experiment for mineral-water interfaces is a hurdle, as surface functional group type and distribution must be accounted for in determining mechanisms. Additionally, computational methods that can describe the substrate are often not appropriate to capture aqueous effects. Progress requires focusing on well-studied and relevant systems, such as key facets (001), (012), and (110) of hematite and alumina, and ubiquitous contaminants such as aqueous Pb. In the past, bulk-parameterized bond-valence principles were used to rationalize Pb(II) adsorption trends. These approaches can break down at surfaces, where flexible bonding environments and adsorption-induced surface relaxations play a critical role. Here, we adapt and apply a density functional theory (DFT) and thermodynamics framework, integrating DFT-calculated energies with experimental data and electrochemical principles, to predict Pb(II) adsorption. Our model results capture trends across the full set of surfaces and predict that inner-sphere Pb(II) sorption on (001) alumina varies from unfavorable to weakly favorable across a range of pH conditions. This aligns with experimental insights that Pb(II) interacts at that surface through outer-sphere interactions. Extending to Fe(II) adsorption, we demonstrate a coverage-dependent site preference, potentially explaining disorder in overlayers grown by the oxidative adsorption of Fe(II) on hematite (001).

Two-dimensional electronic spectroscopy (2DES) is one of the premier tools for investigating photoinduced condensed phase dynamics, combining high temporal and spectral resolution to probe ultrafast phenomena. We have coupled an ultrabroadband laser source generated with a hollow-core fiber, compressing pulses to have a pulse duration of 8 fs, with a boxcars 2DES interferometer constructed from only conventional optics. The resulting ultrabroad bandwidth and high temporal resolution allow for superior spectral coverage of the typically broad molecular line shapes in the near-IR/visible region in room temperature solutions, and the exploration of the excited state dynamics at the earliest time epoch in complex systems. The new spectrometer is characterized by examining the dynamics of the dye molecule Rhodamine 700 in methanol solution. These data exhibit rich vibrational wavepacket dynamics, with 2DES data unraveling key molecular vibronic couplings between multiple vibrational modes. For the first time in a degenerate broadband 2DES experiment, we demonstrate the implementation of full-wavelength reference detection to correct wavelength-dependent laser intensity fluctuations. The net result is a 4–5× increased signal-to-noise (S/N) ratio compared to data acquired without reference detection, yielding a typical S/N ratio = 28. The increased S/N ratio facilitates more rapid data acquisition and examination of samples at lower optical densities, and thus concentrations, than typically used in 2DES experiments. These advances will help to alleviate the typical high demands on precious samples in 2DES measurements.

The polarization behavior analysis within dielectric materials is crucial for electronics. Here, we reconsidered the Kelvin probe (KP) technique, a widely used method for determining the work function and surface potential of solid materials, for assessing the polarization properties of deformable materials. Unlike impedance spectroscopy (IS), the KP technique measures displacement current by modulating the electrode spacing, rather than electrode potential. By phase-separating KP signal into displacement current and its delayed component (actual current), the KP method is expected to selectively measure polarization properties within the bulk, as the potential drop in the bulk and interface remains constant. We achieved precise phase separation of the KP signal using an optical lever signal synchronized with the electrode vibration as the reference for the lock-in amplifier. The complex dielectric constants ε_r, KP^* and ε_r, IS^* of liquid samples were measured by KP and IS measurement, respectively. For nonpolar octane, ε_r, KP^* was almost equal to ε_r, IS^*. Alternatively, for polar 1-octanol and 2-octanol, ε_r, KP^* was smaller than ε_r, IS^*. We also estimated that the bulk potential drop in 1-octanol and 2-octanol is approximately one-tenth of the total potential drop. The proposed approach offers a novel method for evaluating energy diagrams and provides insights into the polarization mechanisms of deformable materials.

Mechanisms of photoinduced electron/energy transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerizations using zinc tetraphenylporphyrin (ZnTPP) or tetraphenylporphyrin (TPP) as photoredox catalysts (PCs) were studied using density functional theory calculations. To explain the selectivity of ZnTPP for trithiocarbonate compounds, the radical generation mechanisms of two chain transfer agents (CTAs), a trithiocarbonate (BTPA) and a dithiobenzoate (CPADB), were compared. The results suggest that the reaction mechanism (i.e., electron or energy transfer) depends on both the PC and CTA. For the most efficient combination, ZnTPP and BTPA, the reaction proceeds via an electron transfer mechanism. In contrast, TPP reacts with CPADB via an energy transfer mechanism. Furthermore, the formation of a stable complex between intermediates is identified for the reaction of ZnTPP and BTPA. These findings reveal the detailed mechanism and will offer insight into improving the yield and selectivity of PET-RAFT polymerization using porphyrins as PCs.

Chiral tricyclic 6,5,5-fused rings exhibit structural diversity and possess important biological activities in the synthesis of natural products. However, predicting the possible mechanism and origin of stereoselectivity in these reactions remains a challenge. In this article, we conducted a theoretical investigation into the NHC-catalyzed intramolecular [3 + 2] annulations of ynals to generate tricyclic 6,5,5-fused rings. Our calculations revealed that NHC could nucleophilically attack the carbonyl group of the ynal reactant, leading to the formation of a Breslow intermediate via a 1,2-proton transfer. Subsequently, an intramolecular Michael addition takes place, resulting in a 6–5 bicyclic intermediate. We then compared the competitive processes involving proton transfer and the Mannich reaction. The more energetically favorable process involves an HOAc-assisted proton transfer process, followed by the Mannich reaction. To ascertain the origin of the diastereoselectivity, we performed noncovalent interaction (NCI) and atom-in-molecule (AIM) analyses. This work is useful for understanding the general principles and detailed mechanisms of the synthesis of chiral 6,5,5-fused tricyclic scaffolds with unique diastereoselectivity.

Singlet fission (SF) is a phenomenon that generates multiple excitons (triplets) on different chromophores from a single exciton (singlet) on one chromophore. Owing to the strong electronic correlation and a complicated excited state manifold of carotenoids (polyenes), the SF mechanism in carotenoids is different from acenes shown in J. Phys. Chem. Lett., 2022, 13, 6800–6805. However, the mechanism is expected to have significant effects of the geometry in the excited state and strong vibronic couplings between these low-lying excited states. Employing high-level state-of-the-art electronic structure methods, we show that the dark A_g states and charge transfer components play a major role in the SF process. The success of the process is strongly dependent on the relative orientation of the monomers. We have also shown that the high-frequency modes involving changes in bond length alternation are strongly coupled to the excited electronic states. These nuclear vibrational modes facilitate the SF process.

This study develops a generalized method for applying spin–echo small-angle neutron scattering (SESANS) to the structural analysis of polymers. Starting from the theoretical framework of SESANS, we developed real space correlation functions for the Gaussian chain model systems consisting of chains with many beads. Further molecular dynamics (MD) simulations affirm that the functions derived by our proposed theoretical work can accurately predict the radii of gyration of polymer chains, which bring straightforward insight of SESANS measurements. This work will enable a broader application of SESANS in soft matter analysis.

With the ever-growing need to study systems of increased size and complexity, modern density functional theory (DFT) methods often encounter problems arising from the growing computational demands. In this work, we have presented a comprehensive DFT validation of the steered molecular dynamics (SMD) approach in estimating the binding energies of aromatic dimers. By performing DFT calculations on optimized and unoptimized anthracene and rhodamine 6G (R6G) dimers using functionals with progressively enhanced exchange-correlation energy description and comparing the obtained results with SMD-predicted values, it was found that SMD predictions are in good agreement with the results obtained from hybrid DFT calculations. The average binding energies for optimized anthracene dimers were found to be 6.46 kcal/mol using DFT at ωB97X-D4/def2-QZVPP and 7.64 ± 1.61 kcal/mol as predicted by the SMD. For the R6G H-type dimer, the binding energies were 17.48 and 19.02 ± 2.22 kcal/mol, respectively. The study also revealed that due to the lack of explicit terms accounting for electron–electron interactions in MD force fields, the proposed method tends to overbind dimers. It is anticipated that the presented method can be applied to more complex dimers, potentially accelerating the calculations of binding energies. Moreover, this study further validates the accuracy of the CHARMM36 FF.

We point out that although a litany of studies have been published on atoms in hard-wall confinement, they have either not been systematic, having only looked at select atoms and/or select electron configurations, or they have not used robust numerical methods. To remedy the situation, we perform in this work a methodical study of atoms in hard-wall confinement with the HelFEM program, which employs the finite element method that trivially implements the hard-wall potential, guarantees variational results, and allows for easily finding the numerically exact solution. Our fully numerical calculations are based on nonrelativistic density functional theory and spherically averaged densities. We consider three levels of density functional approximations: the local density approximation employing the Perdew–Wang (PW92) functional, the generalized-gradient approximation (GGA) employing the Perdew–Burke–Ernzerhof (PBE) functional, and the meta-GGA approximation employing the r²SCAN functional. Importantly, the completely dissimilar density functional approximations are in excellent agreement, suggesting that the observed results are not artifacts of the employed level of theory. We systematically examine low-lying configurations of the H–Xe atoms and their monocations and investigate how the configurations─especially the ground-state configuration─behave as a function of the position of the hard-wall boundary. We perform calculations with both spin-polarized as well as spin-restricted densities and demonstrate that spin-polarization effects are significant in open-shell configurations, even though some previous studies have only considered the spin-restricted model. We demonstrate the importance of considering ground-state changes for confined atoms by computing the ionization radii for the H–Xe atoms and observe significant differences to earlier studies. Confirming previous observations, we identify electron shifts on the outermost shells for a majority of the elements: valence s electrons are highly unfavored under strong confinement, and the high-lying 3d and 4f orbitals become occupied in atoms of periods 2–3 and 3–4, respectively. We also comment on deficiencies of a commonly used density-based estimate for the van der Waals (vdW) radius of atoms and propose a better behaved variant in terms of the number of electrons outside the vdW radius that we expect will prove useful in future studies.