  Employing a classical density-functional description of liquid environments,
we introduce a rigorous method for the diffusion quantum Monte Carlo
calculation of free energies and thermodynamic averages of solvated systems
that requires neither thermodynamic sampling nor explicit solvent electrons. We
find that this method yields promising results and small convergence errors for
a set of test molecules. It is implemented readily and is applicable to a range
of challenges in condensed matter, including the study of transition states of
molecular and surface reactions in liquid environments.
