Fully self-consistent  ab initio  density functional calculations were performed for clean (100) surfaces. Upon studying 2 x 2 and 2 x 1 reconstructed surfaces, it was found that the symmetrical dimer 2 x 1 geometry was the ground state. The corresponding electronic band structure was calculated within an approximation which took account of many-body quasi-particle effects.

C.Kress, M.Fiedler, W.G.Schmidt, F.Bechstedt: Physical Review B, 1994, 50[23], 17697-700