It was recalled that a particularly important defect in oxides was the O vacancy. Depending upon the electronic structure of the material, the nature of the O vacancies changes markedly. A rationalization was provided here of the very different electronic structures of neutral and charged O vacancies in these oxides; which had completely different electronic structures; from very ionic MgO to largely covalent SiO2. The methods of ab initio quantum chemistry, from density functional theory to configuration interaction, were used to determine the ground- and excited-state properties of these defects. The theoretical results were combined with recent spectroscopic measurements, and various properties were estimated. These included defect formation energies, hyperfine interactions in electron paramagnetic resonance, spectra of paramagnetic centres, optical spectra and surface chemical reactivity. The interaction of experimental and theoretical information permitted the unambiguous identification of the structure of the O vacancies in these binary oxides, and on their surfaces.

Ab initio Theory of Point Defects in Oxide Materials: Structure, Properties, Chemical Reactivity. G.Pacchioni: Solid State Science, 2000, 2[2], 161-79