OXYGEN INTERSTITIALS IN MAGNESIUM-OXIDE - A BAND-MODEL STUDY

The defect energy and configuration of oxygen-atom interstitials in cr ystalline magnesium oxide have been studied within a band model, using the Hartree-Fock linear combination of atomic orbitals method. Specia l attention has been paid to the size of the supercell that is necessa ry to obtain reliable results. Volume-centered, face-centered, and edg e-centered interstitials have been studied. In all three cases the mos t stable defect configuration is the O--O- ''dumbbell'' formed by the symmetrical displacement of one of the nearest-neighbor lattice anions , with a redistribution of charge such that each O atom in the dumbbel l carries a charge of close to -1e. The separation of the two O atoms in the dumbbell depends on its orientation and is between 1.32 and 1.3 8 Angstrom.