SEMIEMPIRICAL CALCULATIONS OF POINT-DEFECTS IN SILICA - OXYGEN VACANCY AND TWOFOLD COORDINATED SILICON ATOM

Structure and electronic properties of oxygen vacancy and twofold coordinated silicon atom in solid silicon dioxide are investigated in a cluster approach by MNDO semiempirical molecular orbital method. Optical absorption and photoluminescence bands are calculated. Two types of the neutral oxygen vacancy are predicted absorbing at 5.3 eV and at 7.8 eV. Calculated properties of the first vacancy agree with the experiment for oxygen-deficient centres in silica glass and may be regarded as a confirmation of corresponding model of these centres. Contradictions between recent tight-binding and ab initio calculations of the oxygen vacancy are resolved.