Atomistic description of electric dipole polarizability in Si _nH_m

A scheme for decomposing the polarizabihty of an atomic cluster into atomistic components is apphed to a series of hydrogenated silicon clusters, Si_nH_m, from SiH₄ to Si₃₅H ₃₆. 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-fransfer parts. The results for the Si_nH_m 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.