A brief review was given of some of the approaches which were used to study the distributions of defect properties in amorphous silica. Attention was focussed on the implementation of the embedded cluster method. Some of the results obtained by using this method were illustrated, and the remaining problems were analyzed by using the example of O vacancy defects in amorphous SiO2. The neutral vacancies were characterized by a wide distribution of formation energies and structural parameters. The modelling predicted the 2 major structural types of positively charged vacancies (E' centres), dimers and dangling bond centres. The local structure for both kinds of centre depended upon the medium-range structure of the surrounding amorphous network. It was found that most of the dangling bond centres were unpuckered. The optical spectra and electron paramagnetic resonance parameters calculated for all defects were in good agreement with experimental data. The structural criteria which favoured the formation of different kinds of centre in the original amorphous structure were formulated in terms of the average Si–O distance of O ion from its 2 neighbouring Si ions.

Structure and Properties of Defects in Amorphous Silica - New Insights from Embedded Cluster Calculations. P.V.Sushko, S.Mukhopadhyay, A.S.Mysovsky, V.B.Sulimov, A.Taga, A.L.Shluger: Journal of Physics - Condensed Matter, 2005, 17[21], S2115-40