Figure 6.

Correlation between the selectivity displayed by a reduced model and the mean canonical coordination number n of Na⁺ or K⁺ (calculated by counting the average number oxygen ligands within 3.0 Å away from K⁺ and within 2.8 Å away from Na⁺). The results for the 1077 reduced models are shown. The color code corresponding to different range of the Na⁺/K⁺ relative free energies is the same as in Fig. 4: highly selective for K⁺ over Na⁺ (ΔΔG_Na,K > +3 kcal/mol, blue circles), weakly selective for K⁺ over Na⁺ (0 kcal/mol < ΔΔG_Na,K < 3 kcal/mol, magenta circles), weakly selective for Na⁺ over K⁺ (−3 kcal/mol < ΔΔG_Na,K < 0 kcal/mol, green circles), and highly selective for Na⁺ over K⁺ (ΔΔG_Na,K < −3 kcal/mol, red circles).