A CORRELATION STUDY OF SODIUM ATOM CHEMISORPTION ON THE SILICON SURFACE

Different possible adsorption sites of sodium atoms on a silicon surface have been investigated using ab initio self-consistent unrestricted Hartree-Fock total-energy cluster calculations with Hay-Wadt effective core potentials. The effects of electron correlation have been included by invoking the concepts of fourth-order many-body perturbation theory and are found to be highly significant. Bare silicon and hydrogen-bonded silicon cluster models have been employed to represent the silicon surface. We find that the Na atom adsorption across a dimer bond at the pedestal site modelled with an NaSi7(4, 2, 1) cluster is most favoured energetically, followed by Na adsorption at the cave site modelled with NaSi8(4, 2, 2). The effects of the charge transfer from Na to the silicon surface are also analysed and discussed.