Defect-free and defective silica were studied by using an ab initio simulation method involving ultra-soft pseudopotentials. Good agreement with experiment was found for the cohesive energy (better than 1eV) and the lattice parameter of a-quartz (better than 0.2%). The use of super-cells permitted the evaluation of the energy of formation and partial molar volume of neutral O vacancies.

Study of Oxygen Vacancies in Silica using Ultra-Soft Pseudopotentials. N.Capron, S.Carniato, G.Boureau, A.Pasturel: Journal of Non-Crystalline Solids, 1999, 245, 146-9