Quantum Monte Carlo calculation of the electronic binding energy in a C60 molecule

Electronic energies are calculated for a Hubbard model on the C60 molecule using projector quantum Monte Carlo (QMC) methods. The calculations are performed to an accuracy high enough to determine the pair-binding energy for two electrons added to neutral C60. The method itself is checked against a variety of other quantum Monte Carlo methods as well as the exact diagonalization for smaller molecules. The conclusion is that the ground state with two extra electrons on one C60 molecule is a triplet, and, over the range of parameters where QMC is reliable, it has a slightly higher energy than the state with electrons on two separate molecules, so that the pair is unbound.