First-principles investigation of the Ca/Si(111)2x1 surface

Atomic and electronic structure of the Ca/Si(111)2x1 surface has been studied by density functional theory calculations. The Seiwatz chain structure with Ca adsorbed on the T-4 site, suggested in previous experiments, is found to be the most stable among the structural models considered. This Seiwatz-T-4 model produces a semiconducting surface band structure: Two filled and one empty surface-state bands are found in the gap originating from the Si dangling-bond states on the Seiwatz chain and the Ca 4s states, respectively, which indicates a complete charge transfer from Ca to the Si surface. The calculated band dispersions agree well with photoemission data, but the simulated scanning tunneling microscopy images, empty-state images of bright stripes representing the one-dimensional Ca chains, and filled-state images of hexagonal lobes representing the Si dangling bonds, partly differ from experimental images of only bright stripes for both empty and filled states.