Konstantin S. Smirnov

Ab initio generalized valence force field for zeolite modelling. 1. Siliceous zeolites

Abstract A new potential permitting the molecular dynamics study of the structural and dynamical properties of siliceous zeolites is presented and tested. It is based on a quantum-chemical derivation of the Cartesian force constants which are transformed into an internal coordinate system and corrected for systematic errors. The calculated vibrational spectra for three siliceous zeolites (sodalite, faujasite and silicalite) show a very satisfactory agreement with the experimental ones and the force field is very similar to a potential recently derived from experimental data.

Ab initio generalized valence force field for zeolite modelling 2. Aluminosilicates

Abstract A generalized valence force field for modelling the vibrational spectra of aluminosilicates is developed on the basis of ab initio calculations (3-21G ∗ and DZP/MP2) performed on small clusters: Si(OH) 4 , (OH) 3 SiOSi(OH) 3 , Al(OH) − 4 , H 3 SiOHAlH 3 , (OH) 3 SiOAl(OH) − 3 and (OH) 3 SiOHAl(OH) 3 . The Cartesian force constants from the ab initio calculations are transformed into internal coordinates and used in molecular dynamics simulations of protonated and non-protonated faujasite structures. Calculated positions of the bands in the infrared and Raman spectra of the zeolite are in good agreement with those observed. The force field explains the main features in the vibrational spectra OH(OD) groups of protonated structures.

Computer simulation study of methane in silicalite

Abstract Characteristics of methane in silicalite were studied by a molecular dynamics technique. The model used takes all degrees of freedom of adsorbate molecules into account, while the zeolite framework was either rigid or flexible. The calculated heat of adsorption, diffusion coefficient, and spectral characteristics of the adsorbate are compared to experimental and previous theoretical data.

Ab initio study of the initial steps of hydrothermal zeolite synthesis and of sol-gel processes

Abstract The initial steps of hydrothermal zeolite synthesis and of sol-gel processes were studied by ab initio calculation of molecular models representing the reagents, intermediates and final products of the reactions. The calculations show that the anionic compounds are more stable than the corresponding neutral compounds. It is proposed that the reaction mechanism involves the polycondensation of anionic species with the subsequent formation of both linear and cyclic chains.

A comparative computer modelling study of spectral characteristics of cation exchanged zeolite Y

Abstract Vibrational spectra of alkali metal exchanged zeolite Y were studied by means of lattice energy minimization and molecular dynamics. Results of the study show that the mid-infrared spectra are better reproduced with a valence force field used in MD calculations in comparison to the data calculated with the shell model employed in the energy minimization procedure. Both methods describe the infrared spectra in the far-infared region well. The calculations reveal that no band in the far-infrared region can be unambiguously assigned to cationic vibrations at a specific site.

Molecular-dynamical calculation of vibrational spectra application to zeolites

Abstract Infrared and Raman spectra of siliceous sodalite, faujasite, zeolite A and silicalite as well as cation-exchanged zeolite A are calculated with the help of molecular dynamics using one unique harmonic force field. The results are very satisfactory and allow a microscopic interpretation of the spectra.

Vibrational spectrum of the geminal hydroxyl groups on a silica surface. A molecular dynamics study

Abstract A molecular dynamics computer simulation was carried out to obtain spectral features of geminal hydroxyl groups on a silica surface. The density of proton vibrational states and IR stretching vibrations were calculated. Four intense peaks at 196, 600, 800 and 3736 cm−1 in the spectra obtained are ascribed to the out-of-plane (196 cm−1) and in-plane (600 and 800 cm−1) bending vibrations and stretching vibration (3736 cm−1). The in-plane bending vibration bands of geminal OH groups reveal a strong temperature dependence, unlike the bands of other vibrations. The experimental verification of the results obtained is discussed.

Infrared study of surface acidity of mildly hydrothermally dealuminated zeolites using the low-temperature adsorption of simple molecules

Abstract Low-temperature adsorption of simple molecules was used to characterize acidic centers of mildly hydrothermally dealuminated H ZSM-5 zeolites. No increase of acidity of Lewis and Bronsted acid sites was found.

Building a Virtual Cluster for 3D Graphics Applications

This paper discusses a possible approach to distributed visualization and rendering system infrastructure organization, based on Linux environment with the usage of virtualization technologies. Particular attention is paid to the minutiae, which may be encountered due to the environment setup and exploitation processes, and may affect system performance and usability. Some applications and development tools are studied, as they can provide a rapid onset of computing resources exploration.

Computer simulation study on isomorphously substituted silicalites

Abstract The influence of isomorphous substitution on the structure and vibrational spectra of the orthorhombic form of silicalite was studied by means of the molecular dynamics technique. Replacement of silicon by model T atoms with the parameters of germanium points to the T3 position as the most preferable one for T atom siting in the structure. The substitution leads to significant changes in the size and shape of the channels so that for the structure with a Si T ratio of 11 the distances between the positions of oxygen atoms that deterimine the dimensions of the straight channels are ca. 7.4 × 9.2 A as compared with ca. 8.1 × 8.4 A for pure silicalite. Analysis of the vibrational spectra reveals spectral regions sensitive to the incorporation of non-silicon atoms into the framework.