Structural determination of Cl chemisorption on Si{111} and Ge{111} by total-energy minimization

The atomic geometry of Cl-Si{111} and Cl-Ge{111} has been determined by total-energy minimization. The calculations are done within the local-density-functional framework with the use of norm-conserving pseudopotentials. Cl is found to be most stable in the onefold-atop position on Si{111} and, in contrast to earlier belief, also on Ge{111}. This result agrees with 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, and vibrational frequencies are predicted.