Electronic and atomic structures of the isomers of endohedral and exohedral fullerene complexes with two lithium atoms

The electronic structures of all the possible isomers of endohedral and exohedral C₆₀ fullerene complexes with two lithium atoms are theoretically investigated. It is found that the electronic structures of these compounds are characterized by an impurity filled-level state determining the band gap. The location of the impurity state and, correspondingly, the band gap of the exohedral fullerene complexes depend on the coordination mode and the distance between the alkali metal ions. A similar dependence is observed for the total energy of the exohedral fullerene complex under investigation.