Oxygen adsorption at anionic free and supported Au clusters

The structure, stability, and O-2 adsorption properties of anionic Au-n (n=1-11) clusters either free or supported at defected MgO(100) surfaces are investigated using density-functional theory. O-2 adsorption is strong whenever unpaired electrons are present, except for at some small, supported, planar, high-band-gap clusters. These clusters have the unpaired electrons pinned by the Madelung potential of the support. Larger clusters (starting at Au-7-Au-8) become three dimensional and metallic. This ensures that while one cluster orbital is pinned to the defect, another orbital at comparable energy can undergo depletion, thus binding O-2 with charge transfer. (c) 2005 American Institute of Physics.