Effect of size and geometry on the electronic properties of small hydrogenated silicon clusters

We have calculated the geometrical characteristics and electronic properties of small SinHm clusters, using the local-density approximation of density functional theory and the pseudopotential approach. Both for passivated crystal fragments and octasilacubane our results indicate nontrivial and so far unexpected effects of the cluster structure on the nature of the low-lying electronic excitations. Comparison with previous calculations as well as with experimental data, where available, is made. For the sake of comparison, calculations on (carbon) cubane are also presented.