Ab Initio Analysis of Silicon Nano-Clusters

Several silicon nanoclusters (Si n, with n in the range 1–96) electronic and charge states are calculated using sophisticated compound methods, such as G1–G4, CBS, and W1, as well as using a flavor of density functional theory with a variety of basis sets. Results are compared with very precise experimental data when available. The B3PW91 hybrid functional yields results of comparable quality with all compound procedures, especially for bond energies, which systematically improve as the size of the basis set is increased. For the very small clusters, we used basis sets containing up to 131 basis functions per Si, which included up to two sets of h -functions. All ionization potentials, electron affinities, and dissociation energies are in good agreement with the experimental results. We perform calculations of the biggest clusters, up to Si 96, using B3PW91/6-31G(d). We calculate second derivatives and thus the vibrational spectra for all clusters, and we generate harmonic force fields for molecular dynamics calculations with these nanoclusters.