OXYGEN VACANCIES ON MGO(100)

The electronic and atomic structures of non-stoichiometric MgO{100} su rfaces, with several densities of neutral oxygen vacancies, have been studied using a semi-empirical Kartree-Fock method associated with a g eometry optimization code. The oxygen vacancies are periodically repea ted in the surface top layer with equal spacings. Strong electron redi stributions take place on the magnesiums which surround the vacancies and localized electron states appear in the gap below the conduction b and minimum. Their positions shift towards lower and lower energies as the vacancy density increases. The energy of formation of a vacancy i s found to be close to 10 eV at low densities. It strongly decreases a s the oxygen deficiency grows, due to electrostatic interactions. The mechanisms responsible for the displacements of the magnesiums which s urround the vacancy are analysed.