Geometries and Vibrational Spectra of Small Hydrogenated Silicon Clusters

Abstract

We report a systematic study of ground state structures, vibrational spectra, cohesive energies and HOMO-LUMO gaps of small Si n H clusters (n=3, 10) based on the nonorthogonal tight-binding molecular dynamics scheme. The ground state structures have been obtained by using simulated annealing. In particular, we focus on how the addition of a hydrogen atom affects the ground state geometry and the stability of a Si n cluster. We find that hydrogen either enters into the surface of the cluster or occupies a position outside the cluster. In the first case, it drastically distorts the cluster, while in the latter, there is very little distortion. We find that in some cases Si n H cluster has some resemblance with Si n+1 cluster. We also find that hydrogen can form bonds with more than one silicon atom. Our calculation indicates that SiH, Si3H and Si5H will be more stable and Si4H , Si6H , Si7H , Si9H and Si10H will be less stable clusters.