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ABSTRACT: Water molecules were removed from the X-ray structure models of zeolites with comparatively small-sized unit cells (BIK, BRE,
EDI, GIS, GOO, LAU, and PHI), and cations were replaced by cations of only one type (Mg or Zn). The dehydrated zeolite models
obtained were optimized with the Bush and Catlow force fields. The dependences of atomic multipole moments up to the fourth
order along the so-called cumulative coordinate were calculated for these models by the density functional method with periodic
boundary conditions. These dependences were used to estimate the electrostatic potential and electric field in the cross section
of a zeolite that was not used to calculate them. The data obtained with atomic charges borrowed directly from calculation
results were quite satisfactory.
Russian Journal of Physical Chemistry 05/2012; 81(4):493-509. · 0.46 Impact Factor
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ABSTRACT: A model for the expansion of a pulsed jet of a mixture of monoatomic gases was advanced on the basis of the Boltzmann kinetic
equation. The Grad method was used to solve the Boltzmann equation. The set of moment equations was analyzed by matching asymptotic
expansions. The behavior of the velocity slip and temperature difference was analyzed as a function of the conditions in the
source and the component-gas concentrations in the mixture. A functional relationship between these quantities and the form
of the interaction potential has been established.
Moscow University Chemistry Bulletin 04/2012; 62(4):191-196.
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ABSTRACT: The dynamics of water hexamer isomerization was analyzed by classic molecular dynamics using TIP4P and TIP5P empirical interaction
potentials. Periodic jump transitions between structural isomers occurred as the internal energy of the cluster grew. Structures
prevailing over the energy intervals corresponding to the quasi-liquid and quasi-solid cluster phases were determined. The
lifetimes of structural isomers were found.
Russian Journal of Physical Chemistry B 04/2012; 3(3):404-409. · 0.26 Impact Factor
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ABSTRACT: The dependence of the volume of the chaotic component in the internal dynamics of triatomic van der Waals clusters on the angular momentum is calculated using the Monte Carlo and molecular dynamics methods. It has been found that this dependence is nonmonotonic and that its functional form varies for different values of the total energy. The effective number of rotational modes was used to clarify why a change in the volume of chaotic component of the phase space happens for certain values of the angular momentum. We conclude that a large fraction of regular trajectories in relation to all trajectories appears only when there is a possibility for the regular motion to perform a rotation different from that for a chaotic motion. When such difference is small, the regular motion disappears. The effective number of rotational modes can be used to estimate the difference in the type of rotation and is a convenient parameter which controls changes in the dynamics of the system.
The Journal of chemical physics 10/2010; 133(14):144101. · 3.09 Impact Factor
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Journal of Computational Chemistry. 01/2010; 31:421-430.
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ABSTRACT: A new series of calcium oxide clusters Ca(2)O(X) (X = 1-4) at cationic positions of mordenite (MOR) and faujasite (FAU) is studied via the isolated cluster approach. Active oxide framework fragments are represented via 8-membered window (8R) in MOR, and two 6R and 4R windows (6R+4R) possessing one common Si-O-Si moiety in FAU. Structural similarities between the Ca(2)O(X)(8R) and Ca(2)O(X)(6R+4R) moieties are considered up to X = 4. High oxidation possibilities of the Ca(2)O(2)(nR) and Ca(2)O(3)(nR) systems are demonstrated relative to CO, whose oxidation over the Ca-exchanged zeolite forms is well studied experimentally. Relevance of the oxide cluster models with respect to trapping and desorption of singlet dioxygen is discussed.
Journal of Computational Chemistry 07/2009; 31(2):421-30. · 4.58 Impact Factor
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ABSTRACT: A new catalytic oxidation cycle over binuclear Zn- and Ca-cation clusters in zeolites is proposed. Intermediate active clusters appear due to trapping of dioxygen. CO oxidation is considered as a model reaction over a cluster located in an 8-membered (8R) ring. Geometries of active clusters involved in the catalytic cycle vary depending on the nature and size of the cation. Reagents, transition states, and products have been optimized at the isolated cluster level considering DFT functionals (B3LYP, B3P86, and B3PW91) with the 6-31G* or 6-311++G** basis sets. Moderate activation energies of 23.0 and 35.7 kcal/mol at the B3LYP/6-31G* level are obtained for CO oxidation over Zn- and Ca-clusters, respectively.
05/2009;
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ABSTRACT: Electrostatic potential (EP), electric field (EF), and electric field gradient (EFG) values are calculated in periodic models of magnesium substituted phillipsite (MgPHI) zeolite forms using periodic DFT (PDFT) hybrid B3LYP level with fourteen different basis sets. Relative root mean square differences between the EP, EF, or EFG values estimated between different basis sets are evaluated in several spatial domains available for adsorbate molecules in the zeolite. In these areas, the EF increase in MgPHI is evaluated relative to all-siliceous PHI types. The EP is interpreted in terms of framework ionicity for MgPHI and all-siliceous PHI models. Angular Si-O-Si dependence of the EFG asymmetry at (17)O atoms in all-siliceous zeolites is discussed.
Journal of Computational Chemistry 05/2008; 29(14):2344-58. · 4.58 Impact Factor
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ABSTRACT: The electrostatic potential (EP) and electric field (EF) are calculated in the TON and CHA zeolites using periodic hybrid B3LYP, PBE, and PW91 functionals considering eight basis sets. Relative root mean square differences between the EP or EF values estimated between the different basis sets are evaluated in several domains available for adsorbate molecules in both zeolites. The EP is interpreted in terms of ionicity of the framework.
Journal of Computational Chemistry 02/2008; 29(1):130-8. · 4.58 Impact Factor
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Journal of Computational Chemistry. 01/2008; 29:2344-2358.
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ABSTRACT: Electrostatic potential (EP) and electric field (EF) values are calculated in periodic models of proton-substituted brewsterite (HBRE) and chabazite (HCHA) zeolite forms using the periodic DFT (PDFT) hybrid B3LYP level with 13 different basis sets. Relative root mean square differences between the EP, or EF, values estimated between the different basis sets are evaluated in several spatial domains available for adsorbate molecules in both zeolites. In these areas, the EF increase in HCHA is evaluated relative to all-siliceous CHA. The EP is interpreted in terms of ionicity of the framework. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
International Journal of Quantum Chemistry 06/2007; 107(15):3137 - 3150. · 1.36 Impact Factor
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ABSTRACT: The dependence of the internal dynamics of triatomic van der Waals
clusters on the rate of nonrigid rotation has been studied. The method of
decomposition of the system's motion into orthogonal modes of the motion has
been proposed. Additionally, a new method of separation of the kinetic energy,
captured by the modes, into rotational and vibrational components has been
developed. It has been found that the most significant factor for the chaotic
behavior of the cluster is the partitioning of the vibrational and rotational
energies among the modes.
The European Physical Journal D 01/2007; 41(2):297-302. · 1.48 Impact Factor
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ABSTRACT: A new way to evaluate the electric field (EF) based on the propagation of multipole moments distributed over atomic sites is illustrated for arbitrary aluminophosphate (ALPO) sieves of ratio Al/P = 1. The atomic multipole moments (AMMs) are evaluated for all crystallographic independent atomic types of 10 ALPO structures within the scheme developed by Saunders and colleagues, considering the electron density computed with the CRYSTAL 98 code at the periodic density functional theory (PDFT) level and different basis sets. In two steps, the method uses the calculated AMMs to calibrate several approximate dependences and permits construction of molecular charge distributions for any sieve. First, atomic charges are evaluated via fitted analytical expressions versus the atomic geometries of the framework. Second, high AMMs up to hexadecapole are approximated for all atomic positions, using a cumulative coordinate scheme. Differences between calculated and approximated EF values within the porous space available for adsorbed molecules are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
International Journal of Quantum Chemistry 09/2005; 105(6):839 - 856. · 1.36 Impact Factor
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ABSTRACT: Available cross section data of electron–molecule processes are scaled to simulate the behavior of the dielectric strength (DS) in SF6 and CF4 gases at the level of the two-term approximation of the Boltzmann equation solution corresponding to the homogeneous electric field model. Then, the DS of mixtures is evaluated and compared to experimental data. The reasons of the synergism and its “asymmetry” relative to both components in SF6/CF4 mixtures are analyzed in terms of rate constant variations with respect to their values for the pure gases as well as in terms of weighted rate constants for all channels of electron energy losses relevant under breakdown conditions. © 2004 American Institute of Physics.
Journal of Applied Physics 06/2004; 96(1):109-117. · 2.17 Impact Factor
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ABSTRACT: Three hydrated aluminosilicate frameworks—LiABW, NaNAT, and BaEDI—are partly optimized with the periodic Hartree–Fock CRYSTAL95 code. In particular, we optimized the positions of the adsorbed water molecules including the positions of the framework cations (ABW, NAT) or part of the framework atomic positions (ABW). This allowed us to compare cation–water clusters in the gas and adsorbed states and discuss the influence of hydrogen bonding to the framework oxygen atoms or to the neighbor water molecules on the atomic properties (quadrupole coupling constant, anisotropy of electric field gradient) of the adsorbed water molecules. The LiBIK structure obtained from X-ray diffraction is also considered to illustrate the hydrogen bonds occurring between adsorbed water molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
International Journal of Quantum Chemistry 03/2003; 92(1):71 - 84. · 1.36 Impact Factor
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ABSTRACT: The effect of the spatial anisotropy in the distribution of components of particle momenta of the rotating Ar3_3 cluster is studied at a given total energy and different values of the total angular momentum. The Schwarzschild formula applied to describe this distribution gives three parameters which can serve as a measure of the internal temperatures of the cluster. A new definition of the energy of the overall non-rigid rotation based on the Schwarzschild distribution is proposed.
Zeitschrift für Physik D 10/1997; 42(2):131-134.
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ABSTRACT: The effect of total rotational angular momentum on the stochastic characteristics of the internal motion of rare-gas trimers has been studied by the molecular-dynamics method. Results presented for the argon trimer described in a two-parameter phase space characterized by fixed values of the total energy and angular momentum provide insight into the separation of chaotic from regular motions of the system. An important feature of the phase-space structure is that the volume filled by regular trajectories for fixed total energy of the system is not a monotonic function of its total angular momentum. The chaotic motions are characterized by a strong coupling between potential- and kinetic-energy contributions that is not observed for the regular motions.
Phys. Rev. A. 63(4).
