  We explore different ways of incorporating accurate trial wave functions into
free projection auxiliary field quantum Monte Carlo (fp-AFQMC). Trial states
employed include coupled cluster singles and doubles, multi-Slater, and
symmetry projected mean-field wave functions. We adapt a recently proposed fast
multi-Slater local energy evaluation algorithm for fp-AFQMC, making the use of
long expansions from selected configuration interaction methods feasible. We
demonstrate how these trial wave functions serve to mitigate the sign problem
and accelerate convergence in quantum chemical problems, allowing the
application of fp-AFQMC to systems of substantial sizes. Our calculations on
the widely studied $\text{Cu}_2\text{O}_2^{2+}$ model system show that many
previously reported isomerization energies differ substantially from the
near-exact fp-AFQMC value.
