Large-scaleab initiostudy of the binding and diffusion of a Ge adatom on the Si(100) surface

We identify the binding sites for adsorption of a single Ge atom on the Si(100) surface using ab initio total-energy calculations. The theoretical diffusion barriers are in excellent agreement with experimental estimates. Using a large supercell we resolve the controversy regarding the binding geometry and migration path for the adatom, and investigate its influence on the buckling of Si dimers. We find that the adatom induces a buckling defect that is frequently observed using scanning tunneling microscopy, indicating that the study of a single adatom may be experimentally accessible.