Guest Atom Displacements in Silicon Cluster Na₂@Si₅₀H₄₄

Abstract

We present the displacements of the guest sodium atoms in double caged Na₂@Si₅₀H₄₄ cluster. The cluster consists of a piece of clathrate II consisting of two adjacent Si₂₈ cages filled with guest sodium atoms, being hydrogenated in order to terminate the dangling bonds. Although in a single Si₂₈H₂₈ cage the endohedral sodium atom locates at the center, the sodium atoms in each of the double cage cluster displace about 0.06 nm away from each center of the cages to form a dimer between the endohedral sodium atoms. The displacements are attributed to the formation of covalent bond between the endohedral sodium atoms and the ionic bonding between the sodium atoms and the cage silicon atoms.