Electron-correlation effects on geometrical and electronic structures of Si_nNa clusters

The geometries and energies of silicon-sodium binary clusters (Si_nNa, n = 2-7) were investigated with the inclusion of electron-correlation effects using the second-order Møller-Plesset perturbation theory (MP2) with the 6-31G basis set. In addition, the fourth-order (MP4) energies were evaluated to determine the ground-state isomers. Si₄Na cluster was calculated with the polarized 6-31G* basis set. For all of the Si_nNa clusters, the most stable isomers have bridge-site type structures. Apart from the bridge-site type Si₆Na, the structure of the most stable isomer of Si_nNa keeps the frame of the corresponding Si_n cluster unchanged, and the electronic structure of Si_nNa is similar to that of the corresponding negative ion Si^-_n. The silicon framework of the bridge-site type of Si₆Na is distorted from the compressed octahedron to the face-capped trigonal bipyramid.