A combination of infrared and inelastic incoherent neutron scattering spectroscopies with the density functional theory and semi-empirical calculations was applied to propose an assignment of the vibrational spectra of 4-aminopyridine chloroantimonate(IV).

The results of the interaction of two 60-fullerene molecules interaction under external pressure, studied by a semi-empirical PM3 quantum chemical method, are reported. A set of 15 space structures of 60-fullerene dimers from the simplest one up to partially graphitized material has been simulated. Calculated pressures referring to the dimers’ formation reproduce the experimental order of magnitude rather well. The dependences of the heat of formation and the force ballancing the applied pressure versus compression have been determined. A mechanism of the dimerization is proposed.

Inelastic incoherent neutron scattering spectra of progesterone and testosterone measured at 20 and 290 K were compared with the IR spectra measured at 290 K. The Phonon Density of States spectra display well resolved peaks of low frequency internal vibration modes up to 1200 cm−1. The quantum chemistry calculations were performed by semiempirical PM3 method and by the density functional theory method with different basic sets for isolated molecule, as well as for the dimer system of testosterone. The proposed assignment of internal vibrations of normal modes enable us to conclude about the sequence of the onset of the torsion movements of the CH3 groups. These conclusions were correlated with the results of proton molecular dynamics studies performed by NMR method. The gaussian program had been used for calculations.

Results of inelastic incoherent neutron scattering (IINS) on norbornane are reported. The IINS spectra in the low-temperature phases display low-frequency internal vibration modes very well. The assignment of these modes is proposed in reference to the results of the calculations of the structure and dynamics of isolated molecules by semi-empirical quantum chemistry methods.

The problem of structure of amorphous and/or active carbon is still under discussion and there is no common point of view on this problem. Main part of publications is based on the graphite-like model with some distortions of the perfect crystal [1]. But these models include the undefined precisely ‘irregular or disordered’ part without at least approximate chemical structure of this part. In this work we would like to point our view on this problem from the quantum chemical position and our methodology ‘technology following’ for investigation and simulation of complicated chemical processes [2]. Below we would like to outline main results only due to lack of space for the result discussion. Our program ‘CLUSTER-Z1’, using PM3 method [3] made all computation. Some ab initio calculation was made by PC GAMESS program in MINI basis set. Completed version of this work will be published later.

We describe a new way to simulate the structure of vitreous silica. Using an improved semi-empirical code, we simulate the condensation of SiO2 molecules (typically 27 SiO2 molecules) into aggregates, stopping the computation at the first local total energy minimum. The structure of these aggregates appears to be very disordered with a distribution of coordination number, angle and bond length. It is representative of small particles obtained in any chemical vapour deposition process.

The response of a silicone polymer fragment to external stresses is considered in terms of a mechanochemical reaction. The quantum chemical realization of the approach is based on a coordinate-of-reaction concept for the purpose of introducing a mechanochemical internal coordinate (MIC) that specifies a deformational mode. The related force of response is calculated as the energy gradient along the MIG, while the atomic configuration is optimized over all of the other coordinates under the MIC constant-pitch elongation. The approach is applied to a set of linear silicone oligomers Si-n with n = 4, 5, and 10 subjected to uniaxial tension, followed by the molecule breaking and a postfracture relaxation. Three stages of deformation, differing by structural transformation, have been detected. The observed peculiarities of the oligomer mechanical behavior are well attributed to the characteristic modes of vibrational spectra, The oligomer strength and the related Young's moduli are obtained. A cooperative radical-driven mechanism of silicone polymer fracture is suggested.

Vibrational densities of states of solid xylenes were determined from the inelastic neutron scattering spectra measured on the NERA spectrometer at the IBR-2 pulsed reactor. These spectra were used to test the semi-empirical quantum-chemistry calculations of internal vibrations of xylene molecules with differently deuterated sub-units. Rotations of methyl groups were found to be strongly affected by intermolecular interactions in the crystals and mixed with phenyl ring deformations.

The observed and calculated INS vibrational densities of states for globular molecules of norbornane, norborneole and borneole are compared in the frequency range up to 600 cm(-1). Inelastic incoherent neutron scattering (IINS) spectra were measured at ca. 20 K on the high resolution NERA spectrometer at the IBR-2 pulsed reactor. The IINS intensities were calculated by semi-empirical quantum chemistry method and the assignments of the low-frequency internal modes were proposed.

Two model configurations of a silica supercluster have been considered using two identical quantum-chemical techniques, AM1 and PM3. Differences in the technique parameters allowed to examine the impact of the straightened (AM1) and bent (PM3) configurations of the siloxane chains on the vibrational spectra of the models. Comparing the calculated spectra with the experimental ones, a bent configuration of the siloxane chains of the fumed silica, particles is suggested to be a reality. Quantitative characteristics of the supercluster irregularity are presented in the internal coordinates and the reasons for the fumed silica amorphicity are discussed.

The paper opens a series of publications devoted to a microscopic approach to the intermolecular interaction between fumed silica particles and polydimethylsiloxanes of different structure. The paper presents results on atomic characterization of the surface of both hydroxylated and silylated particles in a supercluster approach. A rhomb-like-four-layer supercluster containing 222 atoms is proposed as the basic unit simulating an individual surface facet of the hydroxylated silica particle with a (111)-like packing of the siloxane elements. The total-energy-minimization procedure for obtaining equilibrated cluster structures has been performed at the level of semiempirical quantum-chemical considerations by using the AM1 method. The optimized basic cluster served as a basis for a microscopic examination of the silylation process. The supercluster characteristics are presented by distribution functions related to atomic charges, bond lengths, and bond angles.

A computer modeling of events that occurred under the scanning tunneling microscope (STM) tip was considered from a chemical standpoint. The DYQUAMOD, semiempirical dynamical-quantum chemical program system, which well manifested itself in a quantitative studying of nano-sized objects, was transformed into the DYQUAFIELD program system involving an external electrostatic field. The fields of changeable configurations were simulated by a set of up to 200 point charges. Atomic system modeling was focused on obtaining local electron density (LED) as well as on the object chemical transformations caused by the field. This article presents the results of simulating LED of differently originated graphite films, of a field action on a set of stable molecules, and of an irreversible in-field reconstruction of the diamondlike film surface, which demonstrates a possible nano-sized memory element creation. © 1996 John Wiley & Sons, Inc.

Comparison calculation of boron impurities, substituting for Si and C sites in cubic SiC, is performed in the framework of the cluster MNDO method. Impurity site preference, equilibrium geometry, potential energy surface, reorientation barriers, Franck-Condon shift, spin and charge density distribution and hyperfine parameters are under consideration. The reasonable values of all calculated parameters support the model of a Jahn-Teller centre with strong coupling for the B-Si impurity. Calculations predict the B-C impurity to be the effective-mass-like acceptor.

A problem of computer modelling of real nanomaterials is considered. An algorithmic approach based on nanomaterial classification and particular properties of every classification mode, including recently observed technological polymorphism, is suggested. The concept is put in practice using the DYQUAMOD program system, based on semi-empirical quantum-chemical methods, which allows the study of structure and vibrational spectra of nano-sized objects. The computing facilities are demonstrated by a few examples concerning some technologically important materials.

Calculations using the self-consistent unrestricted Hartree-Fock-Roothan method are carried out in the MNDO approximation for a cluster of 35 host atoms of cubic SiC with a boron impurity. The equilibrium geometry and the hyperfine and quadrupole constants are obtained and compared with experimental values. The computed parameters reveal the main features of boron impurities in SiC.

The results of a large inelastic neutron scattering (INS) experiment performed for different kinds of the dispersed silicas are presented. The amplitude weighted density of states (AWDS) spectra are obtained from the INS spectra recorded at 10, 80 and 290 K. The two aerosil samples differing twice in specific areas (A380 and A175) as well as the two silica gels with the pore size of 20 and 100 Å (SG20 and SG100) are studied. The results obtained for the “A380-family” of samples consisting of aerosil A380 equilibrated with light and heavy water at relative humidity of 60–70%, dried at 700°C and sintered at 1200°C allowed to separate their AWDS spectra into the siloxan core spectra and spectra of the OH + H2O, H2O and OH shells. These sorts of spectra are got for the silica gels. The AWDS spectra for the aerosils and the silica gels are quite different indicating a big difference in the structure of cores and shells of both the silicas as well as in the water molecule arranging on them. The possibility to tackle the results in terms of the computation chemistry is discussed.