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 Si O2 and MgO, two oxide materials with different structural and electron ic properties, has been studied with cluster models and all-electron w avefunctions. Different embedding schemes have been used to account fo r the effect of the surrounding. The geometrical structure of these po int defects has been determined by full geometrical optimisation. Star ting from the minimum structures, a series of observable properties ha ve been computed, in particular, formation energies, hyperfine interac tions in paramagnetic centres, and optical transitions. All these prop erties, in order to be correctly described, need the extensive use of correlation effects. They have been introduced at various levels: seco nd-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 theoretic al information allows the unambiguous determination of the structure o f oxygen vacancies in metal oxides.