To estimate the total free energy correction, including contributions from outside the clusters, we extrapolate the cluster interaction energy correction to 256 ion pairs. Considering the cancellation of Ewald potential contributions for the solute ion pair, we assume that it is convergent to 1.6 (1.4) kcal/mol. Assuming the dispersion interaction energy (∝ 1 r 6 ) is proportional to the solvent ion density (which is approximately a constant outside the first solvation shell), the spherical integration leads to the expression of dispersion energy correction as a + b/N, where N is the solvent ion pair number. Using the dispersion energy corrections presented in row number 2 of Fig. The Born-Haber cycle scheme for Na + and Cl -ion solvation. The ions are assumed to be solvated from the ideal gas state (g) to liquid state (l) with number density ρ o = 15.61(nm) -3 and T 1 = 1150 K (NVT ensemble). The ideal gas of ions are changed into the NPT ensemble with pressure p o = 1 bar and temperature of 1150 K. Then the temperature of the ideal gases is reduced to T 0 = 298.15 K isobarically. At room temperature the sodium ion is changed to the sodium atom and chloride ion to the chlorine radical. Both atoms are then changed into elements, respectively. The solid state (s) NaCl is formed from component elements at room temperature and 1 bar pressure. Then the solid salt are heated isobarically into the liquid phase (l) at T 1 = 1150 K. The change of free energy from the NVT ensemble (ρ o ,T1) to the NPT ensemble (p o ,T1) of the liquid molten NaCl(l) is neglected. All of the Gibbs free energy changes are from thermodynamic tables, and the total change of the solvation free energy is -163.5 kcal/mol.