ELECTROSTATIC POTENTIALS AND FREE-ENERGIES OF SOLVATION OF POLAR AND CHARGED MOLECULES

Theories of solvation free energies often involve electrostatic potent ials at the position of a solute charge. Simulation calculations that apply cutoffs and periodic boundary conditions based on molecular cent ers result in center-dependent contributions to electrostatic energies due to a systematic sorting of charges in radial shells. This sorting of charges induces a surface-charge density at the cutoff sphere or s imulation-box boundary that depends on the choice of molecular centers . We identify a simple solution that gives correct, center-independent results, namely the radial integration of charge densities. Our concl usions are illustrated for a Lennard-Jones solute in water. The presen t results can affect the parametrization of force fields.