First-principles study of the atomic and electronic structure of the Si(111)-(5x2)-Au surface reconstruction

An alternative model for the Si(111)-Au reconstruction at 2/5 Au coverage is proposed and analyzed using first-principles calculations. This model is based on the structure suggested by Riikonen and Sanchez-Portal [Phys. Rev. B 71, 235423 (2005)], but its periodicity of 5x2 is characterized by the removal of one silicon atom from every 5x2 supercell. It is found that this model and that of Erwin [Phys. Rev. Lett. 91, 206101 (2003)] are very close energetically (< 0.5 meV/A(2)). The key features of angle-resolved photoemission measurement and scanning tunneling microscopy are accounted for in this model. Particularly, the present model reproduces the surface band observed just below the Fermi level. Extra Si adatoms supply electrons that dope this weaker band and cause the system to convert from metallic to insulating, consistent with recent two-phase findings. The occupation of the silicon adatom on the parent surface is calculated to be at most one adatom per two 5x2 unit cells, in agreement with experiment.