Geometries and vibrational spectra of small hydrogenated silicon clusters

We report a systematic study of ground state structures, vibrational spectra, cohesive energies and HOMO-LUMO gaps of small SinH 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 SinH cluster has some resemblance with Sin+1 cluster. We also iind 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.