QMC Calculation of the Electronic Binding Energy in a C60 Molecule

TL;DR

This paper uses projector quantum Monte Carlo to accurately compute the electronic energies of a C60 molecule, determining the pair binding energy and analyzing the nature of the ground state with added electrons.

Contribution

It introduces a high-accuracy QMC approach for calculating electronic energies in C60 and assesses the binding energy of electron pairs, comparing results with other methods.

Findings

The ground state with two extra electrons is a triplet.

The electron pair is unbound within the studied parameter range.

QMC results agree with other computational methods.

Abstract

Electronic energies are calculated for a Hubbard model on the $C_{60}$ 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 $C_{60}$. 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 $C_{60}$ 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.