Geometric structure and optical properties of the GaAs(001)-c(4x4) surface

We consider the electronic structure and optical properties for several geometries of the GaAs(001)-c(4x4) surface using first-principles calculations. We find strong evidence that the best agreement with photo- emission and reflectance anisotropy spectroscopy experiments carried out on surfaces prepared under As4 flux is obtained for a structure containing three Ga-As dimers per unit cell. The standard As-As dimer model yields similar, but distinguishable results, while an asymmetric dimer model is found to yield completely incompatible surface spectra.