Bonding nature of Si7 bicapped pentagon cluster:: Ab-initio study

We clarify the bonding nature in the bicapped pentagon Si, cluster in terms of the Laplacian field of the charge density. The field is effective in identifying the bonding nature in the crystalline state. The held analysis clarifies the bonding nature in the cluster; the bonding between the capped atoms has the strongest covalent nature among the three kinds of bonding and the bonding between the edge atoms on the pentagon has the weakest covalent character among them. The second derivative of the charge density gives no information on the bonding nature.