THE SURFACE-CHEMISTRY OF METAL-OXYGEN INTERACTIONS - A FIRST-PRINCIPLES STUDY OF O-RH(110)

We report on a computational study of the clean and oxygen-covered Rh( 110) surface, based on density-functional theory within the local-dens ity approximation. We have used plane-wave basis sets and Vanderbilt u ltra-soft pseudopotentials. For the clean surface, we present results for the equilibrium structure, surface energy and surface stress of th e unreconstructed and (1 x 2) reconstructed structures. For the oxygen -covered surface we have performed a geometry optimization at 0.5, 1, and 2 monolayer oxygen coverages, and we present results for the equil ibrium configurations, workfunctions and oxygen chemisorption energies . At half monolayer coverage, we find that oxygen induces a (1 x 2) re construction of the surface, while at one monolayer coverage the chemi sorption energy is highest for the unreconstructed surface. Our result s are rationalized by a simple tight-binding description of the intera ction between the O 2p orbitals and the metal valence states. The resu lting bonds are stronger when established with low coordinated metal a toms, and give rise to an effective adsorbate-adsorbate interaction wh en two oxygen atoms are bound to the same metal orbital.