Theory of chemisorption on metallic surfaces: Role of intra-adsorbate Coulomb correlation and surface structure

A theory of chemisorption on metallic surfaces is formulated in the site representation. The influence of the intra-adsorbate Coulomb correlations is investigated and is found to lead to significant changes in the single-particle spectral function as compared to the Hartree-Fock result. Comparison with spectroscopic data is shown to imply the existence of large upwards shift in the adsorbate ionization potential due to screening effects arising from the adsorbate-substrate $e$-$e$ interaction. Thus the relative importance of screening and polarization effects and the intra-adsorbate Coulomb correlation is for the first time extracted unambiguously from spectroscopic data. The use of the site representation allows for a natural introduction of the concept of a "surface cluster" without any need for detaching it from the rest of the metallic substrate. Thus the issue of rebonding the surface cluster to the "indented surface" does not arise, the entire system being treated on the same footing self-consistently. We are able to explicitly exhibit the local nature of bonding and incorporate the influence of the surface geometry without disregard of the important screening and polarization effects characteristic of the substrate. The theory is generalized to take account of the nonorthogonality of the adsorbate-substrate wave functions.