Table I.

K⁺/Na⁺ selectivity by experiment and calculation

Method	Solvent	ΔΔG (kcal/mol)	Selective for
	Formamidea	−0.9	Na+
Experiment	Formamidebc	−0.7	Na+
	NMAbd	−1.1	Na+
	Formamidec (CHARMM27)	0.9	K+
	Formamidec (OPLS-AA)	1.3	K+
Pairwise Additive	NMAe (CHARMM22)	1.6	K+
	NMAcd (CHARMM27)	2.8	K+
	NMAcd (CHARMM27/NBFIX)	4.7	K+
	Formamidec (AMOEBA)	−1.3	Na+
Polarizable	Formamidef (QM/MM)	−2.2	Na+
	NMAd (Drude)	−0.3	Na+

K⁺/Na⁺ selectivity of bulk liquid formamide and NMA as determined by experimental work, pairwise-additive (nonpolarizable) force field calculations, polarizable force field (AMOEBA and Drude) calculations, and QM/MM (hybrid quantum mechanical and molecular mechanical) calculations. Note that the pairwise-additive force field calculations display positive (K⁺) selectivity, whereas all other determinations display negative (Na⁺) selectivity.

^aMarcus, 1983.

^bCox and Parker, 1973, and Schmid et al., 2000.

^cGrossfield et al., 2003.

^dYu et al., 2010a.

^eNoskov et al., 2004.

^fVarma and Rempe, 2008.