Forms of chemisorbed oxygen on Ag(110): Semiempirical investigation by the nddo/mc method

Abstract

Various forms of atomic and molecular adsorption of oxygen on the Ag(110) surface are studied using a four- layer cluster Ag32, which has a structure of an orthorhombic prism. It is shown that a qualitatively correct description of molecular and dissociative adsorption of oxygen allows for metallic properties of silver. A simple and effective method for taking into account metallic properties of a single crystal are suggested. This method involves self- consistent shifts of the one- electron matrix elements of silver atoms by the same value for the purpose of leveling the HOMOs of the cluster against the experimental Fermi level. This procedure reproduces the experimental geometry and the binding energy of atomic adsorption in the bridging position on the long chain of the Ag(110) surface. Additional positions of atomic adsorption on and below the surface are predicted. Molecular chemisorption of oxygen on the Ag(110) surface is investigated. Four different molecular forms of oxygen, whose O- O axis is parallel to the surface, are obtained. According to their electronic structure, all of these forms correspond to peroxide. The most probable structure is the bridged structure over the long chain at an angle of 30‡ to the [001] direction with the binding energy of 9.5 kcal/mole (experimental estimate 9.3 kcal/mole).