We use the doped fullerenes as an example of how realistic systems can be described by simple models. Starting from the band structure we set up a tight-binding model that describes the t1u conduction band. Adding correlation terms we arrive at a generalized Hubbard Hamiltonian that we treat using quantum Monte Carlo. To address the problem of superconductivity in the doped fullerenes, we study the screening of a point charge. We find surprisingly efficient metallic screening even for strong correlations, almost up to the Mott transition, and discuss the implications on superconductivity, in particular the effect of the efficient screening on the Coulomb pseudopotential and the electron-phonon coupling.
 

Physica A, 280 166-73, 2000.