Large-scale ab initio modelling of defects in perovskites: Fe impurity in SrTiO3

Abstract Using the unrestricted Hartree–Fock method and supercells containing up to 160 atoms, we calculated the energy level positions in the gap and atomic geometry for the Fe 4+ impurity substituting for a host Ti atom in SrTiO 3 . In agreement with experiment, the high-spin ( S =2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacement mode of the six nearest O ions which is a combination of the Jahn–Teller and breathing modes. A considerable covalent bonding between the Fe ion and the four nearest O ions takes place.