The energies and configurations of O interstitials in crystalline samples were studied by using a band model, together with the Hartree-Fock linear combination of atomic orbitals method. Particular attention was paid to the size of the super-cell that was required in order to obtain reliable results. Volume-centered, face-centered and edge-centered interstitials were studied. It was found that, in all 3 cases, the most stable defect configuration was the O--O- dumb-bell that was formed by the symmetrical displacement of one of the nearest-neighbor lattice anions. The redistribution of charge was such that each O atom in the dumb-bell carried a charge that was close to -1e. The separation of the two O atoms in the dumb-bell depended upon its orientation, and was between 0.132 and 0.138nm.

R.A.Evarestov, P.W.M.Jacobs, A.V.Leko: Physical Review B, 1996, 54[13], 8969-72