First-principles pseudopotential methods were used to study coordination defects in amorphous and hydrogenated amorphous material, as well as their formation and evolution during H interaction. An accurate analysis of the valence charge distribution and of the electron localization function permitted the resolution of possible ambiguities in the bonding configuration. In particular, the method was used to identify 3-fold (T3) and 5-fold (T5) coordinated defects clearly. It was found that electronic states in the gap could be associated with both types of defect and that, in both cases, interaction with H could reduce the density of states in the gap.

Coordination Defects in Amorphous Silicon and Hydrogenated Amorphous Silicon - a Characterization from First-Principles Calculations M.Peressi, M.Fornari, S.De Gironcoli, L.De Santis, A.Baldereschi: Philosophical Magazine B, 2000, 80[4], 515-21