Partial Optimization of Adsorbates on Clusters: Oxygen on Al(111)

Abstract

Using our recently developed partial optimization algorithm we apply ab initio SCF cluster calculations to investigate surface atom relaxation effects for O on Al(111). Like in LEED experiments we find an outward expansion of the surface like atoms in the optimizations of the bare Al10, Al18 and Al19 clusters. When we optimize the position of oxygen in Al18O keeping all the Al atoms at their bulk like geometries we obtain results similar to those of previous workers. However, when we include O and its Al nearest neighbors in the partial optimization we find large changes in the Al18O electronic structure, including the O- anion changing to O2- above the surface and the reverse change for O below the surface.