First-principles study on B-12 clusters in Si

The ab initio calculation is reported on the B-12 clusters in crystalline Si, whose existence has:been recently suggested experimentally. We investigated the atomic and the electronic structures for two possible configurations of B-12 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 B-12 in Si is more stable than the cube-octahedral B-12, although the symmetry of a cubo-octahedron (O-h) is more favorable to crystalline Si than that of an icosahedron (I-h). The calculated results suggest that the experimentally observed B-12 clusters take the icosahedral configuration.