Ab initio simulations of photoinduced interconversions of oxygen deficientcenters in amorphous silica - art. no. 195504

We have studied by ab initio molecular dynamics the interconversion between oxygen deficient centers (Si-Si bond, dicoordinated silicon==Si:, and El c enters) induced by UV irradiation in a-SiO2. By dynamical simulations in th e excited state of a periodic model of a-SiO2 we have identified the reacti on path and activation barrier for the Si-Si --> =Si: interconversion. A ne w competitive transformation of the excited, neutral Si-Si bond into two E' centers has been identified. Our results provide strong theoretical suppor t to the viability of these processes, proposed experimentally on the basis of optical data only.