Lennard-Jones models free-energy perturbation

The MC perturbation method was used to obtain the pmf. The central carbon-Cl distance was defined as r and the free energy changes were computed at 0.125 or 0.25 A intervals with the Cl on the C3 axis. At this point it is clear that there are contact and solvent-separated minima near 3 and 5.75 A with the transition state at about 4 A, as shown in Fig. 5. XRISM calculations reveal a similar shape, although again the XRISM pmf is much flatter than the MC or MD result. Figure 5 also contains the primitive model prediction which is the sum of the Lennard-Jones potentials between the ions and the Coulombic interaction divided by the experimental dielectric constant, 78.4. The importance of the solvent structure is clear. 

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