The bandgap of solid C 60 is found to be 2.3±0.1 eV . The on-site molecular C 60 Coulomb interaction (U) as determined from the KVV C 60 Auger spectrum is found to be 1.6 ±.2 eV . This value of U is shown to be consistent with Frenkel type molecular excitons in the 1.5–2 eV range. These results lead us to suggest that doped C 60 should be considered as a highly correlated system with U/W comparable to that in high T c cuprates. The Auger spectroscpoy results are consistent with a rather long range Coulomb interaction on a single bucky ball indicating that a Hubbard model is not suitable to describe the electronic structure of a C 60 molecule.
High-order correlation effects in the two-dimensional Hubbard model