Vacancy formation and O adsorption at the Al(111) surface

First-principles methods are used to study the vacancy formation energy and its variation with depth, the energetics of the interaction of two point defects, adsorbed oxygen atom and vacancy, as well as substitutional oxygen adsorption at the Al(111) surface. The stability of different configurations of vacancies and oxygen atoms is examined. The vacancy formation energy decreases with the depth of the vacancy. Vacancies in subsurface layers increase the binding of oxygen adatoms in on-surface hollow sites. The surface and subsurface substitutional sites appear to be unstable for oxygen adsorption and are not stabilized by simultaneous on-surface adsorption.