First-principles simulations, based upon density functional theory, were used to

generate silica glasses containing 3.84wt% of water molecules after various quench

protocols. Using the Kohn-Sham density of states, localized states were found in

the band-gap which could be associated with doubly-occupied Si-O dangling bonds

which were negatively charged and were compensated by positively charged

threefold coordinated oxygen. The position of these states above the O 2p valence

band depended upon the local environment of the dangling bonds (and, in

particular, on the presence of other defects in their neighbourhood) and on the

hydrogen-bond length. These native defects, which could exist in optical fibres, were compatible with the optical absorption and photoluminescence bands

observed in amorphous silica, and with their dependence upon the OH content. If

present, these pre-existing defects could play a significant role as precursors in

laser-induced defect formation.

On the Nature of Native Defects in High OH-Content Silica Glasses: a First-

Principles Study. M.Benoit, M.Pöhlmann, W.Kob: EPL, 2008, 82, 57004