ELECTRONIC CORRELATION-EFFECTS IN A FULLERENE MOLECULE STUDIED BY THEVARIATIONAL MONTE-CARLO METHOD

Electron-correlation effects in the fullerene molecule and its ions ar e investigated in the framework of the Hubbard model. The variational Monte Carlo method and the Gutzwiller wave function are used. Most att ention is paid to the case of intermediate interactions, but also the strong coupling limit, where the Hubbard model reduces to the antiferr omagnetic Heisenberg model, is considered for the fullerene molecule. In this case we obtain a very low variational ground state energy. Fur ther, we have calculated the main spin correlation functions in the gr ound state. Only short-range order is found. The pairing energy of two electrons added to a fullerene molecule or to a fullerene ion is also calculated. Contrary to the results obtained by second-order perturba tion theory, pair binding is not found.