A study of the dimer bond on the reconstructed (100) surfaces of diamond and silicon

Cluster calculations of a 4-layer atomic cluster with a single surface pair, using the MNDO and MINDO/3 quantum chemistry programs, are found to lead to a symmetric dimer pair for the clean diamond (100) surface and for hydrogenated C and Si surfaces, in contrast to a Jahn-Teller distorted Si(100) surface. The surface relaxation and dimer bond length, stiffness constant and bond energy are calculated for each case and leads to the identification of the clean diamond dimer bond as a double bond while the other three surface pairs are bound by single bonds. This fact is used to explain the absence of asymmetric distortion of the diamond surface.