Exohedral Bonding Nature of Si Atom on the Ba@Si₂₈ Cluster; Ab Initio Study

Abstract

First-principle electronic structure is studied for the Si₂₈ and Ba@Si₂₈ clusters, which are components of the clusters in silicon clathrate II. We obtain the geometrically optimized relaxed cage structures of the clusters and the exohedral binding nature of single Si atom on the Ba@Si₂₈ clusters. The hollow Si₂₈ cluster relaxes into the Si₂₄ like cluster in the clathrate I having four exohedral Si atoms outside the hexagon in the Si₂₄ cluster. The hexagons on the Ba@Si₂₈ cluster are deformed into a chair type with relaxation. The exohedral Si atom is the most stable at the edge center near the top that meets three pentagons. We have found for the first time that the exohedral Si atom forms the three-center covalent bond between the two caged Si atoms.