Search

Abstract: Density functional theory calculations have been carried out to study the process of NO adsorption on neutral, anionic and cationic Ag8 clusters. Three cluster types have been considered in our study: D2d and Td structures are the most stable isomers in gas phase and C1 structure, which has the geometry of the most stable isomer adsorbed on rutile TiO2 (110) surface. Adsorption energies, N–O bond lengths and corresponding N–O vibration frequencies have been calculated for all structures. It has been shown that in the case of NO interaction with D2d structure the corresponding adsorption energies grow in the following order: E ads(cation)< E ads(neutral)< E ads(anion). The same regularity has been observed for NO interaction with silver tetramers in our previous study. For the Td structure the highest adsorption energy is also observed in case of anionic complex. However, for C1 structure other dependence has been observed: E ads(anion)< E ads(cation)< E ads(neutral). The adsorption of NO on neutral Ag8 cluster (C1 structure) is characterized by the largest N–O bond elongation which should be useful for NO fragmentation process. [ABSTRACT FROM AUTHOR]

Calculations of equilibrium geometry, vertical detachment energies (VDE) and transition energies (Te) from the electronic ground state to excited states of Cun- clusters (n=2–10) have been carried out within DFT model with the new functional developed recently [J. Mol. Struct. (Theochem) 664–665 (2003) 291]. The results of calculations have been compared with observed photoelectron spectra (PHES). The method provides a good agreement between calculations and experiment. For anionic Cu2–10- clusters, the difference between calculated and experimental values of VDE and Te for the most stable isomers does not exceed 0.21 eV. The assignment of previously unknown Cu6-, Cu8-, Cu9- and Cu10- structures has been made by both total energy calculations and comparison of experimental and calculated PHES. The electronic sructure, geometry and energetic characteristics of low-lying isomers have been studied. [Copyright &y& Elsevier]

A comparative analysis of bond lengths (re), vertical detachment energies (VDE), excitation energies of neutral clusters with geometry of anions (Te) and vertical ionization potentials of neutral clusters (IPv) calculated within density functional theory (DFT) using different functionals with both effective core potential (ECP) and all-electron basis sets for silver clusters Agn, n≤6, have been carried out. DFT methods provide a good agreement between calculated and experimental data of some characteristics. The accurate prediction of all characteristics simultaneously can be achieved with all-electron DZVP basis set only. A new functional has been developed. It provides results close to experimental data using the moderate basis set. For anionic clusters Ag2–10−, the difference between calculations with this functional and experimental values of VDE and Te for the most stable isomers does not exceed 0.1 eV. Based on both total energy calculations and comparison of experimental and calculated photoelectron spectra, the structural assignment of clusters Ag7−, Ag9− and Ag10− has been made. The electronic structure and geometrical characteristics of the low-lying isomers has been studied. [Copyright &y& Elsevier]

Abstract: The adsorption of Ag n (n =2,4,8) clusters on the partially reduced rutile (110) surface have been studied using DFT slab calculations. The geometry and electronic structure of silver clusters adsorbed near the oxygen vacancy as well as binding mechanism have been investigated. It has been found that the binding occurs through two types of interaction. Firstly, it is the interaction between cluster’s HOMO and surface eigenstates located on hollow-Ti atoms and, secondly, the overlap of MOs of the cluster with bridging oxygen atoms. The first type leads to charge transfer from the adsorbed cluster to the surface, therefore silver particles become positively charged upon adsorption. The second type leads to the deformation of adsorbed silver cluster, thereby increasing the overlap. The interaction between molecular orbitals of the cluster and orbitals of atoms lying at the vacancy is unlikely. It has been shown that the adsorption energy of Ag n clusters on stoichiometric surface are higher than those for reduced surface. Thus, the adsorption of silver clusters occurs preferably on stoichiometric surface far from oxygen vacancies. [Copyright &y& Elsevier]

Abstract: Titanium dioxide with silver nanoparticles deposited on the surface is known to exhibit higher photocatalytic activity than the uncovered TiO2. A study of the electronic structure of such systems is necessary to understand this effect. A quantum chemical study of silver tetramers adsorption on stoichiometric rutile (110) surface has been carried out using periodic DFT calculations. A number of adsorption positions, which correspond to two basic adsorption sites on TiO2 (i.e. bridging oxygen rows and hollow sites) have been considered. The hollow sites turned out to be preferable for Ag4 adsorption. The population analysis has been performed to study mechanism of interaction between Ag4 and TiO2 surface. The binding has been shown to occur mainly through the interaction between cluster HOMO and rutile conduction band eigenstates. A significant overlap between Ag4 HOMO and titanium orbitals has been found in the case of hollow site adsorption, in contrast to adsorption over bridging oxygen rows, where there is only weak binding towards oxygen atoms. The adsorbed cluster has been found to have a significant positive charge, which is a result of a charge transfer into conduction band. [Copyright &y& Elsevier]

Abstract: Based on both total energy calculations and comparison of experimental and calculated characteristics of photoelectron spectra (PHES), the structural assignment of clusters and has been made using DFT model with recently developed S2LYP functional. The calculated characteristics of PHES for the assigned structures are in excellent agreement with the experimental ones. The electronic structure, geometry and energetic characteristics of low-lying isomers have also been studied. The calculated geometrical parameters of and clusters as well as the geometries of earlier established clusters have been compared with the geometrical characteristics of anionic sodium clusters. The structures of anionic silver and sodium clusters have been found to be very similar. The difference has been observed only for . Based on similarity of the geometries of silver and sodium clusters as well as on the comparison of calculated and experimental characteristics of PHES, the geometry of cluster has been assigned. [Copyright &y& Elsevier]

Abstract: Based on both total energy calculations and comparison of experimental and calculated characteristics of photoelectron spectra (PHES), the structural assignment of , and clusters has been made using DFT model with previously developed S2LYP functional. In case of cluster our decisions were also based on similarity of the geometries of copper and sodium clusters. The calculated characteristics of PHES for all the assigned structures are in excellent agreement with the experimental ones. The assigned geometries of and have been compared with those of recently established structures of silver clusters, which turned out to be very similar. In the meantime, the structure of the most stable cluster is significantly distorted in comparison with the structure of cluster. [Copyright &y& Elsevier]