TABLE I.

The performance of the original and the proposed new AM1-BCC atomic charges in combination with the GAFF2 parameters on the hydration free energies of neutral organic solutes in TIP3P water. Expt. stands for experimental; MSE stands for mean signed error; MUE stands for mean unsigned error; PI stands for predictive index; R stands for Pearson’s correlation coefficient; k and b stand for the slope and intercept values when fitting the calculated data (y) vs experimental data (x) with function y = kx + b.

	Expt. data		Original AM1-BCC						New AM1-BCC (ABCG2)
	Data	range	MSE	MUE				b	MSE	MUE				b
Solutes	No.	(kcal/mol)	(kcal/mol)	(kcal/mol)	PI	R	k	(kcal/mol)	(kcal/mol)	(kcal/mol)	PI	R	k	(kcal/mol)
Non-cyclic alkanes	27	1.33	−0.27	0.34	0.56	0.61	0.40	1.27	−0.27	0.34	0.56	0.61	0.40	1.27
Cycloalkanes	9	1.80	−0.29	0.51	0.35	0.36	0.20	1.04	−0.29	0.51	0.35	0.36	0.20	1.04
Alkenes	23	1.92	0.71	0.71	0.79	0.80	0.74	1.02	0.10	0.26	0.88	0.86	1.02	0.07
Alkynes	5	0.87	0.59	0.59	0.43	0.60	0.27	0.80	0.01	0.15	0.95	0.96	0.49	0.16
Aromatic hydrocarbons	38	4.68	−0.80	0.81	0.96	0.98	1.36	−0.21	−0.18	0.32	0.97	0.98	1.20	0.15
Aliphatic chain + chloride	31	4.53	1.24	1.28	0.83	0.84	0.75	1.03	0.14	0.62	0.71	0.76	1.17	0.29
Aromatic ring + chloride	26	3.83	1.65	1.65	0.24	0.17	0.13	−0.31	0.22	0.55	0.89	0.84	0.81	−0.22
Aliphatic chain + bromide	14	3.17	0.93	1.02	0.73	0.83	0.34	0.57	−0.10	0.38	0.80	0.88	0.53	−0.36
Aromatic ring + bromide	4	0.99	0.53	0.53	0.08	0.46	0.47	−0.47	−0.12	0.12	1.00	0.99	1.02	−0.08
Hydrocarbon + iodide	10	2.76	−0.07	0.34	0.91	0.91	0.53	−0.39	−0.02	0.31	0.84	0.90	0.64	−0.27
Eithers	26	5.20	0.83	0.95	0.92	0.90	0.97	0.73	0.12	0.47	0.95	0.94	1.01	0.14
Alkyl alcohols	27	5.66	1.67	1.67	0.88	0.95	0.75	0.51	0.01	0.27	0.86	0.95	0.90	−0.45
Alkene + alcohols	4	0.59	2.13	2.13	0.10	0.05	0.09	−5.67	0.09	0.46	0.21	0.14	0.23	−2.97
Phenols	17	2.90	0.93	0.93	0.73	0.84	0.83	−1.25	−0.16	0.36	0.86	0.92	0.91	0.39
Ketones	21	4.35	0.27	0.37	0.97	0.94	0.74	−0.68	−0.01	0.32	0.96	0.93	0.82	−0.65
Aldehydes	16	2.20	0.02	0.44	0.90	0.81	1.16	0.53	−0.20	0.34	0.96	0.83	0.85	−0.68
Esters	41	7.82	−0.63	0.75	0.97	0.95	0.87	−1.11	−0.22	0.35	0.97	0.98	1.07	0.04
Amines	23	6.10	1.50	1.55	0.82	0.78	0.90	1.02	0.14	0.48	0.96	0.94	1.09	0.57
Anilines	8	4.02	0.34	0.47	0.85	0.89	0.80	−1.47	−0.08	0.20	0.98	0.98	0.95	−0.34
Pyrazines and pyridines	19	2.83	1.15	1.15	0.67	0.60	0.94	0.86	0.34	0.38	0.71	0.89	1.09	0.75
Nitriles	5	0.58	1.44	1.44	1.00	0.90	2.00	5.23	0.10	0.14	1.00	0.90	1.12	0.56
Nitro compounds	18	9.13	2.03	2.04	0.94	0.94	0.90	1.44	−0.11	0.37	0.98	0.98	0.94	−0.47
Nitrooxy compounds	10	6.52	2.18	2.18	0.92	0.95	0.58	0.45	0.07	0.42	0.96	0.97	0.88	−0.41
Amides	8	3.19	1.57	1.57	0.98	0.98	0.90	0.63	0.25	0.29	0.95	0.95	0.93	−0.46
Thioethers	7	0.62	1.18	1.18	0.42	0.60	0.62	0.61	−0.12	0.23	0.34	0.26	0.37	−1.06
Thiols	5	1.56	0.48	0.48	0.85	0.98	0.90	0.33	−0.06	0.20	0.85	0.97	0.66	−0.54
Sum	442	15.11	0.65	1.03	0.91	0.92	0.86	0.27	−0.03	0.37	0.98	0.98	0.98	−0.06