First-principles studies on clean and oxygen-adsorbed Ir(110) surfaces

Using density functional theory in combination with an ab initio atomistic thermodynamics approach the structure and stability of Ir(110) surfaces in contact with an oxygen atmosphere have been studied. Besides the unreconstructed surface, (1×2)-, (1×3)-, and (1×4)-reconstructed Ir(110) have been considered. We find that without adsorption of oxygen all reconstructed surfaces are more stable than Ir(110)-(1×1). Adsorption of oxygen with coverages higher than 0.5 ML removes the surface reconstruction, leading to either a c(2×2) or p(2×1) oxygen overlayer on the unreconstructed Ir(110) surface and therefore an adsorbate-induced lifting of the reconstruction. While on almost all surfaces oxygen prefers binding at bridge positions to Ir atoms of the topmost layer, on the reconstructed surfaces higher coverages are required to additionally stabilize oxygen at adjacent threefold sites. Besides the stability of surface structures, our studies also reveal quantitative information on the geometry and energetics, providing further insights into the sometimes controversial discussion of oxygen adsorption on Ir(110).