SURFACE BAND-STRUCTURE OF SI(111)2X1

The surface band structures of the three-bond scission (TBS) model and the Pandey-chain (PC) model have been computed using an ab initio Hartree-Fock program crystal 92. In the case of the bulk energy bands, the method gives the correct shapes and structure but overestimates the valence-band dispersion by about 50%. For the TBS model, the calculated valence-band dispersion came out about 50% wider than measured experimentally. This would suggest that the model is consistent with optical data. In the case of the PC model, the valence-band dispersion was qualitatively similar to those of previous calculations, but the width discrepancy was large. The method overestimates the surface band gap for both TBS and PC models. The significance is discussed. © 1995 The American Physical Society.