Intramolecular charge disproportionation and the band structure of A(3)C(60) superconductors

Realistic electronic model calculations provide convincing evidence for intramolecular charge disproportionation of the LUMO (lowest unoccupied molecular orbitals) band structure in the <Fm(3)over bar m> family of A(3)C(60) (A = K, Rb, Cs) superconductors. The conventional LUMO band splits into three similar subbands showing an overall occupied bandwidth of 1 eV and a steep decrease of the density of states at the Fermi level when the band population deviates from half filling. The disproportionation effect results also in nonzero Jahn-Teller distortions, inhomogeneous charge distribution among carbon atoms, and low frequency reorientation modes of Jahn-Teller distortions on each fullerene sites.