Na⁺/K⁺ selectivity free energies at various ion positions.

The ΔΔGsel(Na+ → K+) values are obtained from FEP calculations using Eq 1 (in units of kcal/mol). FW and BW refer to the forward and backward FEP calculations, respectively. The final result in the last column is obtained from the average of the FW and −BW. Star in the last two rows indicate that the FEP calculations are performed for the K1237A analog of the NaV1.4 model.