Electronic energies are calculated for a Hubbard model on the C60 molecule using projector quantum Monte Carlo (QMC). Calculations are performed to 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 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, has a slightly higher energy than the state with electrons on two separate molecules, so that the pair is unbound.
@article{arxiv.cond-mat/0411422,
title = {QMC Calculation of the Electronic Binding Energy in a C60 Molecule},
author = {Fei Lin and Jurij Smakov and Erik S. Sorensen and Catherine Kallin and A. John Berlinsky},
journal= {arXiv preprint arXiv:cond-mat/0411422},
year = {2009}
}