Bonding and stabilities of small silicon clusters: A theoretical study of Si7–Si1

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Abstract
Ab initio calculations have been performed to study the structures and energies of intermediate‐sized silicon clusters (Sin, n=7–10). All geometries have been optimized at the Hartree–Fock (HF) level of theory with the polarized 6‐31G* basis set. The harmonic vibrational frequencies have been evaluated at the HF/6‐31G* level of theory. Electron correlation effects have been included by means of fourth order Mo/ller–Plesset perturbation theory. The most stable structure for Si7 is a pentagonal bipyramid and the lowest energy calculated structures for Si8–Si10 correspond to capped octahedral or prismatic geometrical arrangements. The evolution of the cluster geometries with increasing size is discussed. Clusters containing four, six, seven, and ten atoms have been identified as ‘‘magic numbers’’ for small silicon clusters, both theoretically and experimentally. The hybridization and bonding in small silicon clusters is discussed. Our results are used to interpret the recent photoelectron spectra of negative silicon cluster ions.