Ab initio study of oxygen vacancies in BaTiO3

In this paper we present embedded-cluster calculations on singly charged and neutral oxygen vacancies (or F centres) in the oxide perovskite BaTiO3. The simulations include Hartree-Fock theory with MP2 corrections and density-functional-theory calculations for a central quantum defect cluster and a pair-potential description of the embedding lattice. All important defect-induced lattice distortions are taken into account in this way. We discuss the possible electronic states of charged F centres and the effects of nearby acceptor-type defects. It is shown that isolated oxygen vacancies induce electronic deep-gap levels. Scenarios are discussed to account for shallow-gap levels observed experimentally.