The results of these simulations can be seen in Figure . The reaction coordinate, ξ, is defined as the difference in the distance R 1 between one Cl -and C atom of CH 3 Cl in the reactant side and the distance R 2 between the other Cl -and C atom of CH 3 Cl in the product side. The profiles are compared to the experimental reaction barrier. The reaction barrier by our AIMD/cDFT method with PBE is 16.9 kcal/mol while the reaction barrier obtained from our AIMD/cDFT method with PBE0 is 24.8 kcal/mol, which is in very good agreement with the experimentally observed solution phase reaction barrier of 26.5 kcal/mol 81 and the calculated barrier of 26.6 kcal/mol from the QM/MM simulations with SRP model. Not surprisingly, the hill (i.e., reaction barrier) of the reaction pathway from the PBE0 simulation is higher (and usually more accurate) than the PBE simulation, whereas the valleys are nearly the same. These trends agree with the well-known behavior of DFT, where exchange-correlation potentials without exact-exchange, such as LDA, PBE, and BLYP, tend to underestimate TS/RB energies because the energies for nonbonding interactions are predicted to be too low. On the other hand, TS/RB energies are higher and more reliable with hybrid exchange-correlation potentials (e.g., PBE0, B3LYP, and M062x) and Hartree-Fock theory, which incorporate exact-exchange. Given that the size of the particles involved in the reaction is set using static van der Waals radii, the differences between the solvation effect of each Hamiltonian can mostly be attributed to their electronic nature. Therefore, it is believed that because the PBE treatment drastically underestimated the dipole moment of methyl chloride, it would in turn destabilize methyl chloride solvation which would lead to more energetically unfavorable reactants and a shorter central barrier height. As the reagents of the reactant would be more stabilized due to stronger interactions with the surrounding water, the reaction would appear to have an enhanced central barrier.