Simulation of core-level binding energy shifts in germanium-doped lead telluride crystals

To simulate the changes in core-level binding energies in germanium-doped lead telluride, cluster calculations of the changes in the electrostatic potential at the corresponding centers have been performed. Different locations of the Ge atom in the crystal bulk have been considered: near vacancies, near another dopant site, and near the surface. For calculating the potential in the clusters that model the bulk and the surface of the lead telluride crystal (c-PbTe), the electron density obtained in the framework of the Hartree-Fock and hybrid density functional theory (DFT) methods has been used.     

Electronic excitations of hypervalent configurations in amorphous selenium: Quantum-chemical modeling

The first excited states of the clusters modeling fragments of a continuous random network and the most stable local defects in solid selenium have been calculated by different ab initio methods (TD-DFT, EOM CCSD, CASSCF). A split-valence double-zeta basis set augmented with polarization and diffuse functions has been used. The effect of the cluster size and structure on the energies of transitions is considered, and the tendencies of geometric relaxation of excited states for the most typical structures are assessed.     

Theoretical modeling of oxygen adsorption on the PbTe(001) surface

For the semiconducting compound PbTe, the initial stages of oxidation, which are important for technology of IR-and thermoelectric devices, have been theoretically studied. The structure, stability, and changes in the electrostatic potentials at the oxidized sites in lead telluride have been calculated in the framework of the cluster approach by the hybrid density functional theory B3LYP method. Different variants of attachment of one to six oxygen atoms to the atoms of the surface and subsurface layers have been considered. The most stable oxidation products have been found. The calculation results are quantitatively consistent with experimental XPS data on chemical shifts.     

Hypervalent configurations with dangling bonds in amorphous selenium: Quantum-chemical modeling

Modeling of local defects with dangling bonds appearing in amorphous selenium on the destruction of the continuous random network (CRN) induced by photoexcitation was performed in the cluster approximation with inclusion of correlation effects at the second-order perturbation theory (MP2) level. It was shown that the interaction of moieties with dangling bonds with metastable local defects can lead to the formation of EPR-active structures involving atoms with increased coordination numbers.     

Effect of titanium,antimony, and ruthenium doping on tin dioxide adsorption properties. Quantum-chemical modeling

The influence of the composition of oxides supports on the specific electroactive surface area of Pt in the catalysts, the platinum nanoparticles dispersion, and Pt contents in the catalysts was studied. The Sb-doped SnO₂ oxides with various Sb-doping levels were prepared as a supports of platinum catalysts in polymer electrolyte membrane fuel cells. Density functional theory simulation of Ti, Sb, and Ru doping of tin dioxide and interaction of the doped surfaces with platinum cluster Pt₁₉ have been carried out. All calculations were performed in PBE exchange–correlation functional, with periodic boundary conditions and projector-augmented waves (PAW) basis set. The calculation results were compared with the experimental data X-ray diffraction and transmission electron microscopy (TEM). It was shown that Sb doping of tin dioxide (in quantity of less than 10%, that is, the quantity which cannot provoke significant defects of crystal structure of the supports) leads to a significant increase in a number of platinum clusters adsorbed from the colloidal solution onto the supports surface which results to an increase of the platinum cluster interaction with the supports. The calculated and experimental results are in close fit.     

Quantum chemical modeling of the structure formation and proton transfer in 2-hydroxybenzenesulfonic, 4-hydroxy-1,3-benzenedisulfonic, and 1,3-benzenedisulfonic acids

Hydrate clusters of 2-hydroxybenzenesulfonic and 1,3-benzenedisulfonic acids were calculated in terms of the density functional theory (DFT) by the B3LYP/6-31G** method. The process of water adsorption on the crystal surface of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate was simulated using the generalized gradient approximation (DFT/PBE) and periodic boundary conditions. For the model system (OHC₆H₄SO₃ ^?)·H₅O₂ ⁺, the activation barriers for the proton transfer were calculated depending on the distance between the O atoms and the deviation of the proton from the O...O bond line. The presence of one H₂O molecule per SO₃H group is energetically most favorable for the formation of clusters of 1,3-benzenedisulfonic acid containing a stoichiometric amount of water. The simulation of the hydration of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate (OHC₆H₃(SO₃H)₂·2 H₂O + n H₂O, n = 1–3) showed that the superstoichiometric H₂O molecule is adsorbed on the crystal surface of this dihydrate with energy release of 0.75–0.95 eV. The position of this water molecule is less favorable in the bulk than on the surface.