Figure 4.

The second virial coefficient B₂ as a function of ion pair distance. (a) The black line is B₂ from CPMD PMF; the blue solid line is B₂ of Na-Cl ion pairs from LJ combination rule; the blue dashed lines are the sum of B₂ from all ion pairs; the red line is B₂ of Na-Na pairs and the magenta line is B₂ of Cl-Cl pairs, calculated from the radial distribution of like-charged ion pairs in bulk solution (see supplementary material). (b) The black, red and magenta lines are the same as in Fig a; the green and cyan solid lines are B₂ coefficients of Na-Cl pairs from LJ nbfix and Thole shielding respectively; the green and cyan dashed lines are the sum of B₂ from all ion pairs from LJ nbfix and Thole shielding respectively.