Multiple bonding on C(111)-2×1 surfaces: Surface structural determination from energy minimization

Abstract

The (111) surface atomic structure of diamond is found to be strongly influenced by the ability of C to form multiple bonds. Two structures with different types of C–C bonding were examined. They are: (i) the π-bonded-chain model and (ii) a strongly dimerized version of this model. The surface C–C bonds in these structures are similar, approximately, to those in graphite and the C2 molecule, respectively. The two structures are both stable against small distortions and have nearly equal surface energies of 1.05±0.03 eV per surface atom. The atomic coordinates for the two models, determined from tight-binding based energy-minimization calculations, are given. The accuracy of the tight-binding method in predicting equilibrium bond lengths and energies in graphite and the C2 molecule is discussed.