The numerical results for the IS and PK contributions are shown in panel c of Fig. by presenting the cumulative work computed during the NNIP-MD simulations. Both Na + and Cl -ions share the same PK contribution (24.2 kcal/mol), while the IS contribution to the Na + solvation free energy is -44.7 kcal/mol and that for the Cl -ion is -43.6 kcal/mol.