First-principles investigation of the Ca/Si(111)2×1 surface

Atomic and electronic structure of the Ca/Si(111)2×1 surface has been studied by density functional theory calculations. The Seiwatz chain structure with Ca adsorbed on the T4 site, suggested in previous experiments, is found to be the most stable among the structural models considered. This Seiwatz-T4 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.