ELECTRON-CORRELATION EFFECTS ON GEOMETRICAL AND ELECTRONIC-STRUCTURESOF SINNA CLUSTERS

The geometries and energies of silicon-sodium binary clusters (SinNa, n = 2-7) were investigated with the inclusion of electron-correlation effects using the second-order Moller-Plesset perturbation theory (MP2 ) with the 6-31G basis set. In addition, the fourth-order (MP4) energi es 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 sta ble isomer of SinNa keeps the frame of the corresponding Si-n cluster unchanged, and the electronic structure of SinNa 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.