Theoretical determination of surface atomic geometry: Si(001)-(2×1)

An energy-minimization scheme for the determination of the surface atomic geometry is presented. Hellmann-Feynman forces and total energies are calculated using an ab initio self-consistent pseudopotential approach. When applied to the Si (001) - (21) reconstructed surface, a buckled dimer geometry is found to have minimum total energy. The dimer bond length is shorter than the bulk bond length, suggesting multiple bond character. Comparisons with other structural models are discussed.