Bonding geometries of Cl on Si{111} and Ge{111}

We determine the chemisorption geometry of Ci–Si{111} and Cl–Ge{111} by total energy minimization. The calculations are done within the local‐density‐functional framework using normconserving pseudopotentials. Among the three bonding sites investigated, Cl is found to be most stable in the onefold atop position on both Si{100} and Ge{111}. The calculations confirm the site geometries obtained in recent surface extended x‐ray absorption fine structure (SEXAFS) measurements on annealed surfaces. The calculated substrate–Cl bond lengths are in quantitative agreement with the SEXAFS results. We also predict vibrational frequencies for the Cl–substrate modes which, because of the highly ionic character of the bond, should be easily observable by infrared or energy loss spectroscopy.