First-principles theory of sulfur adsorption on semi-infinite Ge(001)

A self-consistent study of structural and electronic properties of semi-infinite Ge(001) terminated by a monolayer of sulfur is reported. Employing local-density theory together with Green's functions, we find from total-energy minimization that S adsorbs in bridge positions. The electronic spectrum saliently exhibits a dangling-bond and a bridge-bond band, which originate from the four lone-pair electrons at each sulfur adatom. They are both fully occupied. The calculated dangling-bond band is in very good agreement with photoemission data. The bridge-bond band is predicted in this Letter.