Symmetry projection schemes for Gaussian Monte Carlo methods

A sign-free Monte Carlo method for the Hubbard model has recently been proposed by Corney and Drummond. High-precision measurements on small clusters show that ground-state correlation functions are not correctly reproduced. We argue that the origin of this mismatch lies in the fact that the low-temperature density matrix does not have the symmetries of the Hamiltonian. Here we show that supplementing the algorithm with symmetry projection schemes provides reliable and accurate estimates of ground-state properties.