Atomistic Description of Electric Dipole Polarizability in SinHm

A scheme for decomposing the polarizability of an atomic cluster into atomistic components is applied to a series of hydrogenated silicon clusters, Si_nH_m, from SiH₄ to Si₃₅H₃₆. The method is based on the Hirshfeld or "stockholder" approach for defining atomic charge densities. The stockholder densities are used to compute atomic dipole moments and polarizabilities. These are then readily broken into dipolar and charge-transfer parts. The results for the Si_nHm clusters show significant variations in the total atomic polarizability and in the relative importance of dipolar and charge-transfer components for atoms in different locations within the clusters, particularly for atoms near the cluster center in comparison with those near the surface. The charge-transfer contribution to the total cluster polarizability is found to increase in importance with overall cluster size. Removing H atoms from a cluster to create dangling bonds on surface Si atoms increases the atomic polarizability of these atoms, as well as the overall polarizability of the clusters.