GROUND-STATE PROPERTIES OF THE HUBBARD-MODEL ON A C-60 CLUSTER

Using quantum Monte Carlo techniques, we study the one-band Hubbard mo del at half filling, on a C60 molecule. Spin-spin correlations are mea sured at couplings U/t = 4 and 8, and results are compared with simila r studies on square lattices. At the lowest temperatures accessible to our simulations, we find that the spin correlations on the C60 molecu le tend to vanish at large distances, with a correlation length of 3-4 lattice spacings. Spin-wave calculations in the Heisenberg limit are also reported, in qualitative agreement with Monte Carlo simulations. These results suggest that the ground state of the half-filled Hubbard model on the C60 fullerene is spin disordered (defined as having a co rrelation length smaller than the cluster size), in contrast with the spin-density-wave state that exists on the two-dimensional square latt ice. We believe that a ''dimer'' state may properly describe the undop ed C60 molecule.