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To calculate the optical parameters, the finite difference method in the time domain (FDTD) was used, which can be applied to solve Maxwell's equations. A large number of combinations of a planar structure with metal nanoparticles and a structure with nanowires and metal nanoparticles (NPs) were calculated. The height of nanowires h varied from 50 to 3000 nm, the period of the structure P was 100-600 nm, and the diameter of metal nanoparticles d was 50-400 nm. The reduction of light reflection was determined by the anti-reflection effect of the Si-NWs array itself and the direct scattering effect of metal nanoparticles. It was shown that all structures gave significantly lower reflection coefficients compared to that of a solid silicon plate. [ABSTRACT FROM AUTHOR]

Molecular models for tin dioxide nanoparticles containing 1-7 metal atoms and coordinated or constitutive water have been constructed. Dependent on the composition of the models, the coordination number of the tin atom varied from 4 to 6, and that of oxygen was 2 or 3. The considered models contained both terminal (Sn–OH) and bridging (Sn–OH–Sn) hydroxyl groups, and also bridging (Sn–O–Sn) groups. Their equilibrium spatial and electronic structures were calculated using the second-order Møller-Plesset perturbation theory method with the SBKJC valence-only basis set. To assess the gas-phase acidity of the dioxide surface, the deprotonation energy of the studied models was determined. The adsorption energy of water molecules and hydroxide ions on aprotic (incompletely coordinated) tin atoms, which act as Lewis acid centers, was calculated. In order to estimate the pKa value of the surface of tin dioxide, the Gibbs free energy was calculated for the process of formation of ion pairs due to the proton transfer from hydroxyl groups to adsorbed water molecules. Based on the analysis of the energy effects of the coordination of water molecules and of hydroxide ion, the removal of a proton and its transfer on the hydrated surface of tin dioxide, quantitative estimates have been made of the acid-base characteristics of the active sites of the SnO2 surface. The dependence of the acidity of hydroxyl groups and coordinated water molecules on the coordination number of the oxygen atom and the neighboring tin atom, as well as on the dimensions of the cluster model, was revealed. It is shown that the acidity of protonic and aprotic sites naturally decreases with an increase in the coordination number of the tin atom. The method of calculating the value of pKa used in the work for the smallest model of the SnO2.2H2O composition allows one to reproduce the experimental data for stannic acids. [ABSTRACT FROM AUTHOR]

29Si NMR spectra of fullerene-like hollow oligomers of silicic acid were calculated by the density functional theory method using hybrid exchange-correlation functional B3LYP, 6-311+G(2d, p) basis set and GIAO procedure. It is shown that fullerene-like molecule (SiO2)20(H2O)10 gives an intensive signal in the range from -102 to -105 ppm. [ABSTRACT FROM AUTHOR]

A comparative analysis has been performed on the applicability of quantum chemical methods of different complicability to describe the structure and properties of the clean Si(001) surface, and of that containing a few atoms of germanium. It has been found that the density functional theory within the cluster approximation involving the exchange-correlation functional B3LYP and 6-31 G** basis set is the most rational from the point of view of reproducibility of experimentally found results and considering the moderate cost of computing time and computer resources. It is just this approximation of quantum chemical calculations that properly reproduces the lengths of >Si-Si<, >Si-Ge<, and >Ge-Ge< surface dimers bonds as well as the experimentally justified fact of their buckling. [ABSTRACT FROM AUTHOR]

The structure of molecular adsorption complex of O2 molecule on Si(111) face as well as those of the products of its further transformations up to formation of SiO4 - tetrahedron has been examined by means of density functional theory method (B3LYP, 6-31G**) within a cluster approach. Theoretically found IRspectra of the adsorption structures have been compared with available literature data. [ABSTRACT FROM AUTHOR]