We report an experimental refinement of the local charge density at the Si(111) $7\times 7$ 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 $0.26\pm 0.04e^{-}$ from each adatom to the underlying layers, in agreement with full-potential density-functional theory calculations.

• Received 30 December 2008

DOI:https://doi.org/10.1103/PhysRevB.79.193302