Figure 4.

Correlation between the mean ion-ligand interaction (bottom) and the total ion-ligand and ligand-ligand mean energy (top) calculated for the 1077 reduced models for different range of the Na⁺/K⁺ relative free energies: 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).