Vladimir B. Sulimov

Semiempirical calculations of point defects in silica. Oxygen vacancy and twofold coordinated silicon atom

Abstract 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.

UV irradiation-induced structural transformation in phosphosilicate glass

The Raman spectra of phosphosilicate core (P(2)O(5)-SiO(2)) fibers were investigated. Significant changes in the spectra were observed after UV irradiation of the fibers. An interpretation of the photostructural changes confirmed by computer simulation of phosphorus-related centers is proposed.

UV-irradiation-induced structural transformation in phosphosilicate glass fiber

The Raman spectra of phosphosilicate core P2O5–SiO2 fibers were investigated. Significant changes in the spectra were observed after UV irradiation of the fibers. An interpretation of the photostructural changes confirmed by computer simulation of phosphorus-related centers is proposed.

Calculation of soft atomic potentials caused by three-center bonds in silica glass

Abstract Properties of the ue5fcSiue5f8Oue5f8Siue5fc linkage stretched from 0.30 to 0.46 nm in vitreous silicon dioxide are studied with MNDO and PM3 quantum-chemical methods in an isolated cluster model. The soft atomic potential caused by the three-center bond is proved to arise in the stretched linkage. The calculated electronic structure of the three-center bond and vibrational properties of the linkage are discussed.

Calculation of soft atomic potentials formed by three-center bonds in germanosilicate glass

Abstract Properties of the neutral, singly and doubly negatively charged ue5fcGeue5f8Oue5f8Geue5fc linkages and of the neutral ue5fcGeue5f8Oue5f8Geue5fc linkage stretched from 0.34 to 0.46 nm in vitreous silicon dioxide are studied in an isolated molecular cluster model with quantum-chemical methods. The soft atomic potential caused by the formation of three-center bonds between atoms of the linkage is found to arise in the neutral ue5fcGeue5f8Oue5f8Geue5fc linkage stretched to ∼ 0.40 nm. No soft potential is formed in the ue5fcSiue5f8Oue5f8Geue5fc linkage and in the singly negatively charged ue5fcGeue5f8Oue5f8Geue5fc linkage. Capture of a pair of electrons in the ue5fcGeue5f8Oue5f8Geue5fc linkage results in softening of the atomic potential, the soft potential and the three-center bond being formed in the linkage stretched even to 0.38 nm. Results of calculations of electronic structures of the three-center bonds and vibrational properties of the stretched neutral and charged ue5fcGeue5f8Oue5f8Geue5fc linkages are discussed.