Platinum nanoparticles on different types of titanium dioxide surface: A quantum-chemical modeling

The interaction of a Pt₂₉ nanoparticle with pristine and reduced TiO₂ (110), (100), (101), and (100) surfaces in the rutile and anatase modifications has been modeled by the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the interaction energy of platinum particles with stoichiometric surfaces of titanium dioxide crystals is noticeably lower than for tin dioxide crystals. Like for SnO₂, the reduction of the surface leads in some cases to a significant increase in the energy of interaction with platinum. The reoxidation of such structures should result in platinum fixation on the surface.     

Quantum-chemical calculations of electronic structures and molecular properties within the framework of approximate schemes of zero differential overlap

Journal of Structural Chemistry -     

Nonempirical calculations of potential energy-surfaces of the intramolecular rearrangement of LiBX+ and LiA1X+ ions

Institute of New Chemical Problems, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 3, pp. 19–23, May–June, 1989.     

Performance of time-dependent density functional and Green functions methods for calculations of excitation energies in radicals and for Rydberg electronic states

Time-dependent density functional (TD-DFT) and perturbation theory-based outer valence Green functions (OVGF) methods have been tested for calculations of excitation energies for a set of radicals, molecules, and model clusters simulating points defects in silica. The results show that the TD-DFT approach may give unreliable results not only for diffuse Rydberg states, but also for electronic states involving transitions between MOs localized in two remote from each other spatial regions, for example, for charge-transfer excitations. For the. O-SiX(3) clusters, where X is a single-valence group, TD-DFT predicts reasonable excitation energies but incorrect sequence of electronic transitions. For a number of cases where TD-DFT is shown to be unreliable, the OVGF approach can provide better estimates of excitation energies, but this method also is not expected to perform universally well. The OVGF performance is demonstrated to be satisfactory for excitations with predominantly single-determinant wave functions where the deviations of the calculated energies from experiment should not exceed 0.1-0.3 eV. However, for more complicated transitions involving multiple bonds or for excited states with multireference wave functions the OVGF approach is less reliable and error in the computed energies can reach 0.5-1 eV.     

Theoretical and experimental study of the reactivity of PbTe in interaction with oxygen: Effect of germanium impurity atoms

High-resolution X-ray photoelectron spectroscopy (BESSY II, Berlin) has shown that germanium atoms doped into lead telluride are the centers of the oxidation reaction with dioxygen. The structure, stability, and core-level binding energies in the reaction centers have been calculated in the framework of the cluster approach with the use of the hybrid density functional (B3LYP); i.e., theoretical X-ray photoelectron spectra have been obtained. Different variants of the attachment of one to three O₂ molecules to the Ge atom located at the surface of a crystal or in the subsurface layer have been considered. It has been shown that chemisorption leads to structures with close energies, which give rise to a set of components in the spectra with unresolvable binding energies. The calculation and experimental results are in good agreement.     

Oxygen chemisorption on the PbS(001) surface: Quantum-chemical modeling

The structure and stability of local centers involving a different number of oxygen atoms on the surface of crystalline lead sulfide (001) were calculated in the framework of the cluster approach by the hybrid density functional theory B3LYP method. The trends of the formation of such centers and changes in the core electron binding energies for the sulfur and lead atoms constituting these centers were considered.     

Interactions of local hypervalent defects involving chlorine in amorphous selenium: Quantum-chemical modeling

Interactions of intrinsic and extrinsic diamagnetic local defects appearing upon transformation of the continuous random network (CRN) in amorphous selenium doped with chlorine were modeled in the cluster approximation with inclusion of correlation effects at the second-order perturbation theory (MP2) level. It was shown that configurations involving four-coordinate atoms can form combined local defects that are as stable as basic elements of the CRN.     

Dissociative adsorption of molecular hydrogen onto Pt<Subscript>6</Subscript> and Pt<Subscript>19</Subscript> platinum clusters located on the tin dioxide surface: Quantum-chemical modeling

It is suggested that, for the operation of platinum catalysts based on tin dioxide in air hydrogen fuel cells, hydrogen spillover (migration) leading to a change in the electron and proton contributions of the catalyst conductivity is of crucial importance. The hydrogen adsorption, dissociation, and migration in the platinum-tin dioxide-hydrogen system surface have been modeled by the density functional theory method within the generalized gradient approximation (GGA) under periodic conditions using a projector-augmented plane-wave (PAW) basis set with a pseudopotential. It has been demonstrated that the adsorption energy of a hydrogen molecule onto a platinum cluster increases from 1.6 to 2.4 eV as the distance to the SnO₂ substrate decreases. The calculated Pt-H bond length for adsorbed structures is 1.58–1.78 Å. The computer modeling has demonstrated that: (1) the hydrogen adsorption energy on clusters is higher than on the perfect platinum surface; (2) dissociative chemisorption onto Pt _n clusters can occur without a barrier and depends on the adsorption site and the cluster structure; (3) the adsorption energy of hydrogen onto the SnO₂ surface is higher than the adsorption energy onto the platinum cluster surface: (4) multiple H₂ dissociation on the tin dioxide surface occurs with a barrier; (5) the dissociation adsorption of hydrogen molecules onto the platinum cluster surface followed by atom migration (spillover) is energetically favorable.