Adsorption of atomic and molecular oxygen on the MgO (001) surface

Abstract Ab initio calculations based on density functional theory and the pseudopotential method have been used to study the energetics, fully relaxed structure, charge and spin densities, and electronic density of states of adsorbed atomic and molecular oxygen on terraces, steps, corners and reverse corners on the MgO (001) surface. The calculations include spin polarization and gradient corrections, and are performed on periodically repeated systems large enough for the adsorbed species and surface features like steps, corners and reverse corners to be regarded as isolated in most cases. We find substantial binding energies of up to 2.0 eV for atomic oxygen adsorption at oxygen terrace sites and of over 2.5 eV at the surface irregularities. On the terrace, step and corner, the most favorable adsorption mode is for atomic oxygen to bind to a lattice oxygen ion to form a peroxide ion (O 2− 2 ), and the geometry and electronic structure of the ion depend very little on the surface environment. A range of different adsorption sites and orientations for molecular oxygen have been studied but in no case does the adsorption energy exceed 0.2 eV, in agreement with experimental indications. The relevance of our findings to an understanding of oxygen gas-surface exchange is discussed.