  Liquid state theories such as integral equations and classical density
functional theory often overestimate the bulk pressure of fluids because they
require closure relations or truncations of functionals. Consequently, the cost
to create a molecular cavity in the fluid is no longer negligible and those
theories predict wrong solvation free energies. We show how to correct them
simply by computing an optimized Van der Walls volume of the solute and
removing the undue free energy to create such volume in the fluid. Given this
versatile correction, we demonstrate that state-of-the-art solvation theories
can predict, within seconds, hydration free energies of a benchmark of small
neutral drug-like molecules with the same accuracy as day-long molecular
simulations.
