OFF-DIAGONAL INTERACTIONS AND PAIR-BINDING IN SUPERCONDUCTING FULLERIDES

We have examined the effect of including off-diagonal (non-density-den sity) electron-electron (e-e) interactions on putative electronically- driven superconducting states in the fullerides by studying the spectr a of truncated tetrahedral and icosahedral ''Hubbard molecules''. Our perturbation theoretic and exact diagonalization calculations indicate that for moderate screening lengths and intermediate interaction stre ngths these terms can contribute significantly to pair-binding energie s and to energy level splittings, and consequently the occurrence of s uperconductivity in such models is very sensitive to the precise value s of the parameters. We illustrate this in detail in the We also find that, although the individual levels shift substantially, the critical interaction strengths for the Hund's rule violating level crossings a re quite insensitive to the inclusion of these additional interactions .