Ab initio characterization of surface states at the S/Cu(100) interface

S headgroups are present in many organic molecules and realize their adsorption on metallic surfaces. We calculate ab initio the electronic structure of S/Cu(100) adopting the same geometry as that of the S atom in the C7H5NOS molecule on the same surface. The interface, represented by the S overlayer and by the Cu subsurface layer, is characterized quantitatively by the surface state dispersion of the S-Cu hybrids (bonding and antibonding). The role of the S atom as "hook" for the whole molecule is strongly supported by our calculations. Our results are in quantitative agreement with the photoemission results of C7H5NOS on Cu and also in qualitative agreement with more complicated biological adsorbates on different metallic surfaces.