HYPERPOLARIZABILITY OF THE C60 FULLERENE CLUSTER

Motivated by a discrepancy of five orders of magnitude between three different hyperpolarizability measurements on the C60 fullerene, we calculated the optical response of this cluster using a tight-binding Hamiltonian and compared the results to those for a benzene molecule. Our Hamiltonian reproduces the linear polarizability and hyperpolarizability of benzene reasonably well. For C60 our calculations of the bare polarizability agree only with two of the optical response measurements and indicate that the corresponding linear and nonlinear response of C60 is much larger than that of C6H6. We find that screening effects decrease this difference strongly, and also reduce the calculated hyperpolarizability of C60 to a value which is two orders of magnitude below the favored measurements.