Atomic geometry and electronic structure of S/InP(001)

We have performed ab initio pseudopotential calculations of the atomic geometry and electronic states for a monolayer S-covered (001) surface of InP. It is found that for the 1 x 1 periodicity with S in the bridge site, the overlayer-substrate distance between S and In is 1.3 Angstrom and the In-S-In angle is 113.8 degrees. While the calculated In-S-In angle is close to the experimentally deduced value, we find that our prediction of overlayer-substrate distance is smaller than the value obtained from LEED analysis. We also discuss the energetics of formation of long and short dimer bonds for the 1 x 2, 2 x 1 and 2 x 2 reconstructions of the surface.