Atomic structure of the Sb/Si(100)-(2×1) surface

We have determined the atomic structure of the Sb-covered Si(100) surface in one-monolayer coverage using the pseudopotential density-functional total-energy calculation scheme. Within a symmetric dimer model, we find that the equilibrium Sb-Sb dimer bond length and Sb-Si back bond length are 2.94 and 2.59 {}, respectively, in good agreement with a surface-extended x-ray-absorption fine-structure measurement. In addition, the Si substrate recovers a bulklike geometry upon Sb adsorption: atomic displacements from the bulk positions are all within 0.03 {}. We explain a large difference in the experimental Si 2p core-level spectra for Sb/Si(100) and As/Si(100) in terms of the extent of substrate relaxations upon adsorption.