  A novel 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.
