Unusual bridged site for adsorbed oxygen adatoms: Theory and experiment for Ir{100}-(1x2)-O

The structure of oxygen adsorbed on Ir{100} has been determined by density functional theory slab calculations and quantitative low energy electron di ffraction. The two studies produce essentially identical results, experimen t providing a benchmark for the first principles calculation, while the lat ter provides a more complete understanding of the structure. Oxygen forms a (1 x 2) overlayer with adsorption on the bridge site: an unusual result fo r oxygen. There is a significant row pairing of the iridium atoms in the su rface layer which strongly stabilizes the structure, and is one of the main factors favoring the bridge site occupation and the (1 x 2) configuration. (C) 2000 American Institute of Physics. [S0021-9606(00)70623-4].