Structure of the (√3 × √3 )R30° Ag/Si(111) surface from first-principles calculations

The structure of ({}3 ×{} {}3 ) Ag/Si(111) is investigated using first-principles total-energy calculations. The lowest-energy configuration consists of a top layer of Ag atoms arranged as ``honeycomb chained trimers'' lying above a distorted ``missing top layer'' Si(111) substrate. We find that the honeycomb structure observed in scanning-tunneling-microscope images arises from the electronic charge density on an empty surface band near the Fermi level.