First-principles study on clusters in Si

The ab initio calculation is reported on the (Formula presented) clusters in crystalline Si, whose existence has been recently suggested experimentally. We investigated the atomic and the electronic structures for two possible configurations of (Formula presented) clusters; icosahedron and cubo-octahedron. We found that both of the clusters capture the valence electrons, which results in the generation of an unoccupied level in the valence band of crystalline Si. It was also found that the icosahedral (Formula presented) in Si is more stable than the cubo-octahedral (Formula presented), although the symmetry of a cubo-octahedron ((Formula presented)) is more favorable to crystalline Si than that of an icosahedron ((Formula presented)). The calculated results suggest that the experimentally observed (Formula presented) clusters take the icosahedral configuration.