HARTREE-FOCK AB-INITIO STUDY OF THE GEOMETRIC AND ELECTRONIC-STRUCTURE OF RUS2 AND ITS (100)-SURFACE AND (111)-SURFACE

The electronic and geometric structures of bulk RuS2 and its (100) and (111) surfaces, represented by slabs, have been studied with Hartree-Fock periodic calculations. The optimum bulk geometry is in good agreement with crystallographic data and the elongation of the S-S bond compared with the S-2 molecule is analyzed in terms of molecular orbital populations. The (100) and (111) surfaces are calculated to be very different. The (100) surface is very stable, does not give any significant geometric relaxation and its electronic structure shows rather small differences with the bulk case. On the contrary the (111) face has a larger formation energy, shows a marked relaxation compared to the bulk termination geometry and its density of states is characterized by surface states. This is related to the presence of broken S-2 pairs at the (111) surface which therefore shows a potentially higher reactivity.