Theoretical study of small silicon clusters: Equilibrium geometries and electronic structures of Si(n)(n=2-7, 10).

The geometries and energies of small silicon clusters have been investigated in a systematic manner by means of accurate ab initio calculations. The effects of polarization functions and electron correlation have been included in these calculations. Several geometrical arrangements and electronic states have been considered for each cluster. All the geometries have been completely optimized with several basis sets at the Hartree- Fock level of theory. Single point calculations have been performed at these geometries using complete fourth-order perturbation theory with the polarized 6-31G* basis set. The effects of larger basis sets including multiple sets of polarization functions have been considered for Si(2) and Si(3). Singlet ground states are found for Si(3)-Si(7) with the associated geometries corresponding to a triangle, a planar rhombus, a trigonal bipyramid, an edge-capped trigonal bipyramid, and a tricapped tetrahedron, respectively.