Tight-binding calculations of quasiparticle wave functions for C(111)2x1

Despite the simplicity of the system, the description of the excited-state properties of the cleavage surface of diamond requires the use of nonstandard treatment of many-body effects. Using a simple tight-binding model, we show that the typical assumption concerning the identity of quasiparticle and Kohn-Sham wave functions fails in an important part of the Brillouin zone. This simple model allows computation of the qualitatively different quasiparticle wave functions. The optical properties calculated with these wave functions at the Bethe-Salpeter level show important excitonic effects. Moreover the line shape of the reflectance anisotropy spectrum is significantly improved when compared to the measured one.