The electronic and atomic structures of non-stoichiometric {100} surfaces, with various densities of neutral O vacancies, were studied by using a semi-empirical Hartree-Fock method and geometrical optimization. The O vacancies were situated periodically in the surface upper layer, with even spacings. Marked electron redistribution took place at the Mg atoms which surrounded the vacancies, and localized electron states appeared in the gap; below the conduction band minimum. Their positions shifted to lower and lower energies as the vacancy density increased. The formation energy of a vacancy was found to be close to 10eV at low densities. It decreased sharply as the O deficiency increased; due to electrostatic interactions.

Oxygen Vacancies on MgO(100). E.Castanier, C.Noguera: Surface Science, 1996, 364[1], 1-16