FORMS OF CHEMISORBED OXYGEN ON AG(110) - SEMIEMPIRICAL INVESTIGATION BY THE NDDO MC METHOD/

Various forms of atomic and molecular adsorption of oxygen on the Ag(1 10) surface are studied using a four-layer cluster Ag-32, which has a structure of an orthorhombic prism. It is shown that a qualitatively c orrect description of molecular and dissociative adsorption of oxygen allows for metallic properties of silver. A simple and effective metho d for taking into account metallic properties of a single crystal are suggested. This method involves self-consistent shifts of the one-elec tron matrix elements of silver atoms by the same value for the purpose of leveling the HOMOs of the cluster against the experimental Fermi l evel. This procedure reproduces the experimental geometry and the bind ing energy of atomic adsorption in the bridging position on the long c hain of the Ag(110) surface. Additional positions of atomic adsorption on and below the surface are predicted. Molecular chemisorption of ox ygen on the Ag(110) surface is investigated. Four different molecular forms of oxygen, whose O-O axis is parallel to the surface, are obtain ed. According to their electronic structure, all of these forms corres pond to peroxide. The most probable structure is the bridged structure over the long chain at an angle of 30 degrees to the [001] direction with the binding energy of 9.5 kcal/mole (experimental estimate 9.3 kc al/mole).