부산대학교 도서관

Ab initio calculations have been performed to study the structures and energies of intermediate-sized silicon clusters (Si/sub n/, 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 Moeller--Plesset perturbation theory. The most stable structure for Si/sub 7/ is a pentagonal bipyramid and the lowest energy calculated structures for Si/sub 8/--Si/sub 10/ 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.