APPLICATION OF MOLECULAR-MODELS TO ELECTRONIC-STRUCTURE CALCULATIONS OF DEFECTS IN OXIDE CRYSTALS .1. STRUCTURAL MODEL FOR SILICON DIOXIDE

Ab initio and INDO methods are applied to investigate the interaction between several SiO//2 molecules and for electronic structure calculations of idealized beta -cristobalite within the framework of the cluster model. Stoichiometric fragments are chosen for simulating perfect and imperfect crystal structures of SiO//2 by means of combinations of interacting structural units O-Si-O. The boundary conditions for such clusters are imposed in the form of the electrostatic fields in the rest of the crystal. The results of the electronic structure calculations are only slightly dependent on size and shape of the chosen clusters and agree quite well with experimental data.