Interaction effects in magnesium oxidation: a lattice-gas simulation

The oxidation of magnesium proceeds in several stages, beginning with the oxygen dissociation process and ending with the formation of magnesium oxides. Our focus is on the intermediate oxidation state at the magnesium (0 0 0 1) surface. Our calculations show that the oxygen atoms adsorbed into on-surface or subsurface sites form dense clusters. We find that isolated oxygen atoms and small clusters prefer to adsorb into on-surface sites. However, for clusters larger than a few oxygen atoms the oxygen–oxygen interaction effects drive the oxygen atoms into the magnesium subsurface layers and bulk. We use density-functional calculations to characterize our model parameters: surface and subsurface oxygen-site adsorption energies and the corresponding oxygen–oxygen interaction energies. Monte Carlo simulations identify the optimal distributions of oxygen as a function of concentration.