In a previous study by Gray-Weale et al., it was noted that the DFT calculation over-estimates the Na atom solvation free energy in liquid Na by -19 kcal/mol and the total Gibbs free energy change for the redox reaction Na(l)+ 2 Cl 2 (g) ⇀ ↽ NaCl(l) by -15 kcal/mol. The molten salt density is over-estimated by up to 10% when using the PBE DFT functional with the D2 dispersion correction, while the system appears to be unstable without the D2 correction. These results indicate both the importance and the subtlety of dispersion forces in the molten salt liquids. It is not surprising that the over-estimation of the density correlates with the over-estimation of the magnitude of the excess free energy. Some over-binding is also observed in ion solvation for the aqueous solution. Herein to estimate the correction for the free energy based on the underlying DFT simulations, we implement higher-level density-fitted MP2 theory 68 calculations over 400 cluster configurations with the basis set aug-cc-pvdz in the Psi4 package. The cluster configurations with 7 and 17 solvent ion pairs are carved from a trajectory generated by the DFT simulation.