The surface structure of the (111)-(7 x 7) reconstruction was calculated by using an ab initio pseudopotential total-energy technique which involved treating slab models having various geometries and thicknesses. It was shown that a convergent surface topography could be obtained only when the slab was sufficiently thick. That is, when more than 5 layers were allowed to relax. The resultant surface topography was found to be consistent with the experimental results of low-energy electron diffraction, scanning tunnelling microscopy and non-contact atomic force microscopy. It was concluded that the present observation explained a discrepancy between experimentally observed image contrast and previous results of ab initio calculations.

Surface Topography of the Si(111)-7x7 Reconstruction. S.H.Ke, T.Uda, K.Terakura: Physical Review B, 2000, 62[23], 15319-22