Diffraction refinement of localized antibonding at the Si(111) 7×7 surface

We report an experimental refinement of the local charge density at the Si(111) 7×7 surface using a combination of x-ray and high-energy electron diffraction. This method can be generally applied to the charge-density refinement at surfaces of other materials. By perturbing about a bond-centered pseudoatom model, we find experimentally that the adatom electrons occupy antibonding-like backbond states with the atoms below. We are also able to refine a charge transfer of 0.26±0.04e^- from each adatom to the underlying layers, in agreement with full-potential density-functional theory calculations.