A systematic study was made, of the reconstruction of the (100) surface, on the basis of total energies which were calculated within the framework of the local density approximation. Particular attention was paid to the extent to which total energy differences could be reliably calculated by examining such differences for the ideal surface and for 4 proposed reconstructions. These were the p(2 x 1) symmetrical, p(2 x 1) asymmetrical, p(2 x 2) and c(4 x 2) forms. The calculations were performed by using norm-conserving pseudopotentials, and a plane-wave basis. The convergence of the total energy differences was assessed by varying the energy cut-off that was used to truncate the plane-wave basis, and the number of sampling points which was used to perform Brillouin zone integrals over a large range. The effect of optimizing atomic geometries as a function of the energy cut-off and density of Brillouin zone sampling points was determined. Apart from the p(2 x 2) and c(4 x 2) reconstructions, whose energies differed by only 0.003eV/dimer, it was possible to determine unambiguously the energy ordering of the 5 systems which were studied. Disagreements between previous calculations were explained in terms of the differing energy cut-offs and Brillouin zone samplings which were used.

A.Ramstad, G.Brocks, P.J.Kelly: Physical Review B, 1995, 51[20], 14504-23