1ST-PRINCIPLES CALCULATIONS OF ADATOM BINDING AND INTERACTION ON RH(001)

The self-consistent scattering-theory approach to adsorption energetics is applied to light atoms, H and S, on a transition-metal surface, Rh(001). A single H adatom is predicted to bind in a four-fold hollow at a height of 1.23 bohr above the outer Rh layer, with a symmetric stretch frequency of 98 meV in the harmonic approximation. A single S atom binds in a fourfold hollow at a height of 2.77 bohr above the surface, indicative of covalent adsorption. Two H atoms fixed at their isolated-adatom equilibrium positions on Rh(001), but in neighboring fourfold hollows, are well screened from each other and hardly interact at all. Under the same conditions, a H and a S adatom are subject to a repulsion of 0.17 eV.