The electronic structure of clusters modelling the adsorption complexes of the oxygen molecule on single isolated and adjacent anionic vacancies of the (110) face on the surface of rutile was studied. It was concluded that two types of such adsorption complexes exist on the defective surface of rutile.

Advantages and disadvantages of two approaches to electronic structure calculations of molecules using the NDDO approximation are revealed.

Time-resolved luminescence characteristics of the two groups of complex cross-luminescent (CRL) fluorides, namely, BaF2-based (BaY2F8, BaY2F8RE3+ (RE = Ce, Nd, Er, Tm, Yb)) and KF-based fluorides (KYF4, KLuF4, K2YF5, KLiYF5, KLiLuF5 and K2LiGaF6) have been investigated under pulsed synchrotron radiation excitation at 100 K and 300 K. It was found that in BaY2F8 the emission of self-trapped excitons was considerably quenched at 300 K compared with that of BaF2 and the present “slow” emission was caused by uncontrollable rare earth admixtures. In Yb3+-doped BaY2F8 this emission is strongly quenched providing good fast scintillation characteristics. The studied KF-based complex crystals show intensive CRL at 300 K with the spectrum situated mainly in the far VUV spectral range. Data on the new CRL crystals KLiYF5 and KLiLuF5 are reported.

Time-resolved luminescence studies of several new multi-component crossluminescence crystals as well as La1-xCexF3 (x = 0.4 divided by 0.9) crystals have been carried out under vacuum UV (10 divided by 30 eV) and soft X-ray (h nu similar to 1 keV) synchrotron radiation excitation. The band structure parameters of the studied crossluminescence crystals have been estimated by using the spectral data obtained. The non-monotonic dependence of the light yield on x has been observed for La1-xCexF3, the optimum value of x being near 0.7. The result is discussed on the basis of different models of Ce3+ emission quenching.

The quantum-chemical method SCF MO LCAO in the MNDO approximation has been used to investigate the spatial and electronic structure of borosiloxane and aluminosiloxane oligomers that are formed in the original stages of polymerization of silicic acid in the presence of boron or aluminum atoms. An analysis has been made of the energetics of the polycondensation process, the charge redistributions, and the Brönsted acidities O these systems.

By means of the quantum-chemical MO LCAO SCF method in the valence approximation of MNDO, it has been shown that effective interaction of two molecules of Si(OH)4 is possible with the participation of a water molecule that plays the role of a bridge in forming a six-center complex.

The state of boron impurity ions introduced into the matrix of f ine silica in the hydrosol-formation stage was investigated by11B NMR spectroscopy. It was determined that the boron ions, having isomorphically replaced silicon ions, are in tetrahedral coordination. The conclusion that boron ions are preferentially incorporated in the silicon-oxygen matrix in tetrahedral coordination rather than trigonal was confirmed by data of quantum-chemical calculations carried out by the self-consistent-field linear-combination-of-atomic-orbitals molecular-orbital (SCF LCAO MO) method in a valence approximation of modified neglect of diatomic overlap (MNDO) with complete optimization of the geometric parameters of the corresponding molecular structures.

On the basis of the π-electron approximation we have investigated the dependence of the calculated dipole polarizability of molecules on the configurational composition of the variational wave function. The values which were closest to the results of complex configurational interaction were obtained for sets including the single-determinant Hartree-Fock function and all the bonding doubly excited configurations constructed from the localized MO, and also from the complete set of singly and doubly excited configurations.

Using the INDO method we obtained the equilibrium structure of bis(ethylenedithiol) tetrathiafulvalene (BEDT-TTF), studied the properties of its electronic distribution, and determined the ionization potential of the BEDT-TTF molecule.

The spatial structure of the molecule of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) has been determined by the semiempirical SCF-MO-LCAO method in the all-valence-electron MNDO approximation with the use of the formalism of the restricted Hartree-Fock method, and its principal energy and charge characteristics have been calculated.

Internal rotation in phosphoramide and 0,0-dimethyl phosphoramidate molecules in their different stable conformations was studied by different quantum-chemical methods. Rotation of the amide group about the P-N bond is inhibited with barrier values of ∼27 kJ/mole.