EFFECTS OF LONG-RANGE ELECTROSTATIC POTENTIAL TRUNCATION ON THE FREE-ENERGY OF IONIC HYDRATION

The free energy of sodium ion hydration calculated from computer simul ations employing both the molecular potential truncation and Ewald sum mation methods for evaluation of long-range electrostatic interactions disagree by 20%. The discrepancy between the free energies determined by both techniques is found to be methodological, resulting from an i mbalance in the molecular potential truncation scheme that biases the interaction of the water-oxygen and hydrogens with the ion unequally. A simple physical model is proposed and an analytical expression deriv ed to correct this discrepancy. (C) 1997 American Institute of Physics .