Identification of the Au coverage and structure of the Au/Si(111)-5x2 surface

We identify the atomic structure of the Au/Si(111)-5x2 surface by using density functional theory calculations. With seven Au atoms per unit cell, our model forms a bona fide 5x2 atomic structure, which is energetically favored over the leading model of Erwin, Barke, and Himpsel [Phys. Rev. B 80, 155409 (2009)] and well reproduces the Y- and V-shaped 5x2 STM images. This surface is metallic with a prominent half-filled band of surface states, mostly localized around the Au-chain area. The correct identification of the atomic and band structure of the clean surface further clarifies the adsorption structure of Si adatoms and the physical origin of the intriguing metal-to-insulator transition driven by Si adatoms.