Ab initio calculation of geometry and bonding for overlaid and inlaid models of Si(001)/Sb(0.25 ML)-c(4 × 4)

Recent experimental work has revealed the existence of a c(4×4) reconstruction of the Si(001)–Sb surface in the Sb coverage range between 0.2 and 0.3 monolayers. The best fit to the experimental data was found with a structural model in which Sb dimers are adsorbed above the Si(001) dimer rows (overlaid above row structure), although a structure in which Sb dimers are incorporated into the top Si layer (inlaid structure) also fitted reasonably well. In a previous theoretical work we have shown the overlaid geometry to have the lowest surface free energy of a number of structural models considered, with the inlaid structure coming a close second. In this work we present a detailed discussion of bonding information for both of these models.