Pairing on small clusters in the peierls-hubbard model: implications for C/sub 60/

Summary form only given. We study the pairing within the Peierls-Hubbard Model for electron- and hole-doped analogs of C)/sub 60/ accessible to exact diagonalization techniques (cube, truncated tetrahedron, etc.) and larger systems in a truncated basis including C)/sub 60/ in double CI. We find that there exist two different mechanisms of pairing, corresponding to pairing occurring at small U (and vanishing at large U), and to pairing occurring only at large U. We find that the small-U pairing found in the pure Hubbard model cannot be discussed without simultaneously discussing the Jahn-Teller distortions of the Hubbard molecules: when electron-phonon interactions are included, the pairing vanishes. The large-U pairing, surprisingly, is related neither to Jahn-Teller distortion nor to antiferromagnetism. We also discuss potential pitfalls in the extrapolation from small system calculations to C/sub 60/, and stress the necessity of having the correct intuitive picture.