Cluster model calculations of oxygen vacancies in SiO2 and MgO -: Formation energies, optical transitions and EPR spectra

The electronic structure of neutral and charged oxygen vacancies in SiO2 and MgO, two oxide materials with different structural and electronic properties, has been studied with cluster models and all-electron wavefunctions. Different embedding schemes have been used to account for the effect of the surrounding. The geometrical structure of these point defects has been determined by full geometrical optimisation. Starting from the minimum structures, a series of observable properties have been computed, in particular, formation energies, hyperfine interactions in paramagnetic centres, and optical transitions. All these properties, in order to be correctly described, need the extensive use of correlation effects. They have been introduced at various levels: second-order perturbation theory (MP2), configuration interaction (CI) or density functional theory (DFT). However, the quantitative description of the observable properties requires 'correct' structural models of the oxygen vacancies. The interplay between experimental and theoretical information allows the unambiguous determination of the structure of oxygen vacancies in metal oxides.