Electronic states of group-IV endohedral atoms in C28.

Abstract

We have systematically studied the interaction between the C 28 fullerene molecule and the group-IVA endohedral atoms C, Si, Ge, and Sn, using state-of-the-art electronic structure and total-energy calculations based on density-functional theory. We find no covalent bonding between these atoms and the fullerene cage. The nature of the cage-atom interaction involves charge transfer from the endohedral atom to the cage which produces weak, mostly ionic binding. The degree of charge transfer increases with the atomic number of the endohedral atom. By comparing the electronic structure of the group-IVA endohedral cage compounds to Zr@C 8 (a group-IVB endohedral), we find that the latter bonds strongly to the cage due to a covalent interaction betwen the Zr 4d states and the C 28 states