Oxygen vacancies in SiO2 had long been regarded as bistable, forming a Si-Si dimer when neutral and a puckered configuration when positively charged. First-principles calculations of O vacancies in amorphous SiO2 super-cells revealed a significantly more complex behavior. It was found that the vast majority of O vacancies did not pucker after capture of a hole, but were shallow traps. The remaining vacancies exhibited two distinct types of puckering. Upon capturing an electron, one type forms a metastable dipole, while the other collapses to a dimer. A statistical distribution of O vacancies was obtained, and the implications for charge transport and trapping in SiO2 were considered.Structure, Properties and Dynamics of Oxygen Vacancies in Amorphous SiO2. Z.Y.Lu, C.J.Nicklaw, D.M.Fleetwood, R.D.Schrimpf, S.T.Pantelides: Physical Review Letters, 2002, 89[28], 285505 (4pp)