It was noted that density functional theory now permits the calculation of structural and energetic quantities related to non-stoichiometric oxides. Using, as examples, solutions of O in Si, sub-stoichiometric TiO2-x and vacancies in silica, it was shown that, in spite of severe requirements in terms of computational effort, these calculations furnished insights into the nature of defects and their contribution to the macroscopic properties of non-stoichiometric oxides.

Density Functional Theory Study of Point Defects in the Si-SiO2 System and in Substoichiometric Titanium Dioxide TiO2-x. N.Capron, G.Boureau: International Journal of Quantum Chemistry, 2004, 99[5], 677-84