Coulomb and exchange interactions in C60n

Semiempirical modified-neglect-of-differential-overlap (MNDO) quantum chemistry calculations are performed for the negative ions of an isolated C 60 . The value computed for the first electron affinity is in excellent agreement with experiment. MNDO predictions of the energies of the low-lying states of C 60 2- and C 60 3- allow us to extract an effective on-site repulsion U 0 ∼3 eV, and a direct exchange interaction K∼50 meV for C 60 . These values are used to estimate the effective on-site repulsion and dielectric constant of solid C 60 , with results in good agreement with experiment