Localized orbital approach to chemisorption: H and O adsorption on Ni, Pt and W(001) surfaces

Abstract

Atomic orbitais and an atomic approximation to the potential are used in the chemical pseudopotential secular equation to calculate the covalent binding energy of an adsorbed monolayer on a transition metal slab. After showing that the method provides a realistic description of the bulk metal band structure we examine the changes which accompany adsorption in various surface arrangements. For H on W(001), maximum coverage is found to correspond to occupation of all bridge sites (β 1 phase). Bridge sites also provide maximum covalent binding at lower coverage but energy differences between alternative sites are small (~0.2 eV per H atom) and ionic effects may stabilise adsorption above atoms in the β 2 phase. On Ni and Pt(001) both adsorbates bind most strongly above 4-fold hole sites, but for hydrogen energy differences between alternative sites are particularly small (~0.1 eV on Pt). Surface densities of states are presented and discussed in relation to photoemission spectra and the mechanism of the chemisorptive bond.