Correcting for electrostatic cutoffs in free energy simulations: Toward consistency between simulations with different cutoffs

The use of electrostatic cutoffs in calculations of free energy differences by molecular simulations introduces errors. Even though both solute–solvent and solvent–solvent cutoffs are known to create discrepancies, past efforts have mostly been directed toward correcting for the solute–solvent cutoffs. In this work, an approach based on the generalized reaction field formalism is developed to correct for the solvent–solvent cutoff errors as well. It is shown using a series of simulations that when the cutoff lengths are significantly smaller than the half unit cell size, and the solute–solvent cutoff is not much larger than the solvent–solvent cutoff, the new algorithm is able to yield better agreement among simulations employing different truncation lengths.