Table 1. Deviations in Computed Proton Affinities from G3B3 Values, for Protic IL Cations 1–8^a.

	Cation Proton Affinity (kcal/mol)
	1 (n = 0)	2	3	4	5	6	7	8	MADb	max dev
6-31G(d)
PBE	12.8	11.2	9.7	–0.4	11.3	11.3	13.4	14.1	10.4	14.1
B3LYP	12.7	11.5	10.2	–0.5	12.0	12.0	13.7	15.6	10.9	15.6
M06-2X	10.4	9.0	7.8	–3.0	8.7	8.5	–0.3	10.2	6.5	10.4
MP2	13.8	13.6	13.4	0.5	14.7	14.6	15.7	17.7	13.0	17.7
6-31+G(d)
PBE	9.2	8.1	6.9	–4.8	7.3	7.3	9.2	9.5	6.6	9.5
B3LYP	8.3	7.7	6.9	–5.7	7.1	7.1	8.7	9.9	6.2	9.9
M06-2X	6.9	6.1	5.2	–7.1	4.9	4.6	6.0	5.6	4.0	6.9
MP2	11.5	11.6	11.5	–2.3	11.5	11.5	12.8	13.9	10.3	13.9
6-31++G(d)
PBE	9.2	8.2	7.0	–4.8	7.4	7.4	9.2	9.5	6.6	9.5
B3LYP	8.3	7.7	6.9	–5.7	7.1	7.1	8.6	9.9	6.2	9.9
M06-2X	6.9	6.2	5.3	–7.1	4.9	4.7	6.0	5.6	4.1	6.9
MP2	11.6	11.8	11.7	–2.3	11.6	11.6	12.8	13.9	10.3	13.9
6-311G(2d,2p)
PBE	12.4	11.4	10.5	–0.8	11.8	11.8	13.2	14.1	10.5	14.1
B3LYP	11.6	11.1	10.5	–1.7	11.8	11.7	12.9	14.8	10.3	14.8
M06-2X	9.5	9.2	8.8	–3.9	8.6	7.8	9.6	9.6	7.4	9.6
MP2	15.8	16.1	16.6	2.5	16.4	16.5	17.2	19.0	15.0	19.0
6-311++G(2d,2p)
PBE	9.7	9.4	8.9	–3.8	9.6	9.7	11.0	11.1	8.2	11.1
B3LYP	8.5	8.7	8.6	–5.1	9.3	9.3	10.4	11.4	7.7	11.4
M06-2X	7.0	7.3	7.3	–6.6	6.5	6.5	7.6	6.9	5.3	7.6
MP2	13.8	14.5	15.2	0.2	14.4	14.6	15.4	16.5	13.1	16.5
DFTB2/mio-0-1	–7.5	–8.6	–9.0	–19.3	5.9	4.7	4.9	0.5	2.7	9.0
DFTB3/mio-0-1	–4.2	–3.0	–1.9	–16.4	13.1	12.0	8.8	6.2	4.1	13.1
DFTB3/3ob-1-1	–1.9	1.1	3.9	–13.8	16.0	14.8	11.1	9.8	5.6	16.0
G3B3	214.2	221.5	226.1	227.8	229.3	234.2	245.5	214.4

^aEnergies are given as E^method – E^G3B3.

^bMean absolute deviation.