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VO 2 is well known for its low-temperature metal-insulator transition between two phases with tetragonal rutile and monoclinic structure. The adsorption of CO on the two polymorphs of Mo-doped VO 2 is calculated to investigate the effect of a substrate phase change on the adsorption energy. The system is investigated theoretically at density-functional theory level using a hybrid functional with London dispersion correction. We establish a computational protocol applicable for the study of physisorption on open-shell transition metal oxides. The main task is to control the spin state of open-shell slab models used to model adsorption of closed-shell molecules in order to obtain numerically stable adsorption energies and to reduce spin contamination within the broken-symmetry unrestricted Kohn-Sham approximation. Applying this procedure, it is possible to identify the most stable adsorption positions of CO on both phases of VO 2 . CO adsorbs vertically with the C atom on a surface V atom in the monoclinic phase with an adsorption energy of -56 kJ/mol. The same adsorption position has an adsorption energy of only -46 kJ/mol on the rutile phase. Similar differences were obtained with multireference methods using an embedded cluster model. This effect may inspire experimental strategies exploiting the rutile ↔ ${ \leftrightarrow }$ monoclinic VO 2 phase transition in catalytic processes where CO is formed as product or as an intermediate., (© 2022 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Transition-metal-(TM-)doped TiO 2 has been considered as promising electrode material for the oxygen evolution reaction (OER). OER activity is expected to depend on the coordination of the surface atoms. In this study, we theoretically investigate the stability of low-index surfaces of TM-doped rutile, (110), (100), (101) and (001), with 50 % of the Ti atoms substituted by Sc, Y, V, Nb or Ta. For Sc and Y, we also consider models with O vacancies providing the most stable oxidation state of Sc and Y. Surface energies are calculated with DFT(+U). Based on the Gibbs-Wulff theorem, the shape of the single crystals is predicted. It is observed that p-doping leads to spontaneous oxygen loss and O vacancies cause surface reconstruction. The Wulff shapes of n-doped TiO 2 have smaller contributions of the (110) facet and, for Nb and Ta, larger contributions of other facets. Given the higher coordinative unsaturation of the TM atoms in the latter, a higher catalytic activity is expected., (© 2022 The Authors. Published by Wiley-VCH GmbH.)

Vanadium dioxide is an interesting and frequently applied material due to its metal-insulator phase transition. However, there are only few studies of the catalytic activity and surface properties of different VO 2 polymorphs. Therefore, we investigated the properties of the surfaces of the most stable VO 2 phases theoretically at density-functional theory level using a self-consistent hybrid functional which has demonstrated its accuracy for the prediction of structural, electronic and energetic properties in a previous study. We found that the surfaces of the rutile R phase of VO 2 are not stable and show a spontaneous phase transition to the monoclinic M 1 phase. Doping with Mo stabilizes the surfaces with rutile structure even for small dopant concentrations (6.25 %). Both M 1 and R surfaces strongly relax, with and without doping. In particular the metal-metal distances in the uppermost layers change by up to 0.4 Å. Mo segregates in the topmost layer of both R and M 1 phases. The electronic structure is only slightly changed upon doping., (© 2021 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

The G0W0, evGW0, evGW, and scGW0 approximations to many-body perturbation theory combined with the Bethe-Salpeter approach (BSE) are applied to calculate electronic and optical properties of the open-shell spinel ferrite ZnFe 2 O 4 . The effect of the various degrees of self-consistency is assessed by comparison to recent experimental results. Furthermore, the influence of the method for obtaining the ground-state wavefunction is studied, including the GGA functional PBE with and without an intermediate step using the COHSEX approximation, as well as PBE+U, where we try to minimize the influence of the Hubbard potential U. Best agreement for the optical band gap and the first maxima of the excitation spectrum is obtained with the evGW method based on a PBE+U wavefunction. This method is chosen and converged carefully to yield quantitative results for the optical spectra of four different magnetic structures and cation distributions of ZnFe 2 O 4 . With the results we provide a possible explanation for inconsistency in experimental results., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The reliable calculation of the excited states of charge-transfer (CT) compounds poses a major challenge to the ab initio community because the frequently employed method, time-dependent density functional theory (TD-DFT), massively relies on the underlying density functional, resulting in heavily Hartree-Fock (HF) exchange-dependent excited-state energies. By applying the highly sophisticated many-body perturbation approach, we address the encountered unreliabilities and inconsistencies of not optimally tuned (standard) TD-DFT regarding photo-excited CT phenomena, and present results concerning accurate vertical transition energies and the correct energetic ordering of the CT and the first visible singlet state of a recently synthesized thermodynamically stable large hybrid perylene bisimide-macrocycle complex. This is a large-scale application of the quantum many-body perturbation approach to a chemically relevant CT system, demonstrating the system-size independence of the quality of the many-body-based excitation energies. Furthermore, an optimal tuning of the ωB97X hybrid functional can well reproduce the many-body results, making TD-DFT a suitable choice but at the expense of introducing a range-separation parameter, which needs to be optimally tuned., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report on an erroneous ground state within common density functional theory (DFT) methods for the solid elements bromine and iodine. Phonon computations at the GGA level for both molecular crystals yield imaginary vibrational modes, erroneously indicating dynamic instability-that fact alone could easily pass as a computational artefact, but these imaginary modes lead to energetically more favorable and dynamically stable structures, made up of infinite monoatomic chains. In contrast, meta-GGA and hybrid functionals yield the correct energetic order for bromine, while for iodine, most global hybrids do not improve the GGA result significantly. The qualitatively correct answer, in both cases, is given by the long-range corrected hybrid LC-ωPBE, the Minnesota functionals M06L and M06, and by periodic Hartree-Fock and MP2 theory. This poor performance of economic DFT functionals should be kept in mind, for example, during global structure optimizations of systems with significant contributions from halogen bonds., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The electronic properties of vanadium-doped rutile TiO(2) are investigated theoretically with a Hartree-Fock/DFT hybrid approach. The most common oxidation states (V(2+), V(3+), V(4+), and V(5+)) in different spin states are investigated and their relative stability is calculated. The most stable spin states are quartet, quintet, doublet, and singlet for V(2+), V(3+), V(4+), and V(5+) doping, respectively. By comparing the formation energy with respect to the parent oxides and gas-phase oxygen (ΔE), we conclude that V(4+) (ΔE=145.3 kJ mol(-1)) is the most likely oxidation state for vanadium doping with the possibility of V(5+) doping (ΔE=283.5 kJ mol(-1)). The energetic and electronic properties are converged with dopant concentrations in the range of 0.9 to 3.2%, which is within the experimentally accessible range. The investigation of electronic properties shows that V(4+) doping creates both occupied and unoccupied vanadium states in the band gap and V(5+) doping creates unoccupied states at the bottom of the conduction band. In both cases there is a significant reduction of the band gap by 0.65 to 0.75 eV compared to that of undoped rutile TiO(2)., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dispersion-corrected density functional theory calculations (DFT-D3) were performed for the adsorption of CO on MgO and C(2) H(2) on NaCl surfaces. An extension of our non-empirical scheme for the computation of atom-in-molecules dispersion coefficients is proposed. It is based on electrostatically embedded M(4)X(4) (M=Na, Mg) clusters that are used in TDDFT calculations of dynamic dipole polarizabilities. We find that the C(MM)(6) dispersion coefficients for bulk NaCl and MgO are reduced by factors of about 100 and 35 for Na and Mg, respectively, compared to the values of the free atoms. These are used in periodic DFT calculations with the revPBE semi-local density functional. As demonstrated by calculations of adsorption potential energy curves, the new C(6) coefficients lead to much more accurate energies (E(ads)) and molecule-surface distances than with previous DFT-D schemes. For NaCl/C(2) H(2) we obtained at the revPBE-D3(BJ) level a value of E(ads) =-7.4 kcal mol(-1) in good agreement with experimental data (-5.7 to -7.1 kcal mol(-1)). Dispersion-uncorrected DFT yields an unbound surface state. For the MgO/CO system, the computed revPBE-D3(BJ) value of E(ads) =-4.1 kcal mol(-1) is also in reasonable agreement with experimental results (-3.0 kcal mol(-1)) when thermal corrections are taken into account. Our new dispersion correction also improves computed lattice constants of the bulk systems significantly compared to plain DFT or previous DFT-D results. The extended DFT-D3 scheme also provides accurate non-covalent interactions for ionic systems without empirical adjustments and is suggested as a general tool in surface science., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Using a combination of ab initio and semiempirical methods, adsorption problems on surfaces with large unit cells and low symmetry can still be studied. Here, a hybrid approach of density functional theory (DFT) and Hartree-Fock (HF) was used. As an example, we determined the geometry and the electronic properties of benzoic acid (BA), salicylic acid (SA) and para-salicylic acid (p-SA) adsorbed on MgSO(4).H(2)O (100), which are used as conditioner molecules for the electrostatic separation of minerals. Contrary to general expectations, these molecules are chemisorbed, with binding energies around 1.9 eV, forming bonds through the carboxylic O atom of the COOH groups in a nonplanar geometry, although the surface is a stoichiometric wide-band-gap insulator and the molecules stay intact. In contrast, a planar adsorption geometry turned out to be nonbonding. Bonding takes place by means of surface-molecule resonances due to the overlap of the valence band with molecular orbitals, assisted by a small charge-transfer molecule to the surface of around 0.15e. These combined interactions cause an intramolecular twist between the COOH group and the benzene ring.