Theory of reflectance anisotropy of clean and hydrogenated (001) diamond surfaces

Density-functional theory is used to study the linear optical response of the (001) surface of diamond. The equilibrium atomic configurations of the atomic structures are determined from fully converged self-consistent total energy calculations within the local density approximation. The electron-ion interaction is treated by using norm-conserving ab initio fully separable pseudopotentials in the Kleinman-Bylander form. To account for the excitation aspect quasiparticle shifts are added to the single-particle energies. The influence of hydrogen adsorption is studied using a (2$\times$2) translational symmetry. Optical transitions which involve surface states cause significant resonances in the reflectivity in the visible and near ultraviolet ranges which exhibit a strong polarization anisotropy. Adsorption of hydrogen strongly modifies the atomic structure and optical reflectance of the (001) diamond surface.