. Author manuscript; available in PMC: 2013 Apr 10.

Published in final edited form as: J Chem Theory Comput. 2012 Apr 10;7(4):931–948. doi: 10.1021/ct100684s

Table 7.

9 Proton Affinities with Acidic Nitrogen in kcal/mol: Deviation of DFTB and the NHorg Parameter Set in Comparison to G3B3^a

	G3B3	DFTB2		DFTB3
		γ	γ ^h	γ	diag		full
parameter set^b				calc	calc	fit	calc	fit
HCNH⁺	176.0	−12.4	−14.6	+4.5	+4.3	+0.4	+2.8	+0.2
CH₃CNH⁺	192.3	−14.3	−15.4	+2.9	+2.6	−1.2	+1.9	−0.9
C₅H₅NH⁺	229.5	−17.1	−18.3	+1.3	+0.9	−3.5	+0.4	−2.1
methylimidazoleH⁺	237.3	−12.7	−13.4	+5.3	+5.1	+0.8	+4.7	+2.1
methylguanidineH⁺	249.3	−12.0	−13.4	+0.8	+0.4	−2.2	−0.8	−2.9
NH₃	413.9	+10.4	+10.9	−0.9	−16.8	−0.0	−5.3	−0.2
NH⁺₄	212.3	−24.4	−30.5	−9.2	−13.0	−15.0	−14.4	−15.8
CH₃NH⁺₃	223.3	−26.8	−30.5	−10.2	−11.7	−15.1	−13.3	−15.3
1-aminobutaneH⁺	228.2	−26.7	−29.9	−9.8	−11.4	−14.9	−12.6	−14.6

MUE		17.4	19.7	5.0	7.4	5.9	6.2	6.0
MSE		−15.1	−17.2	−1.7	−4.4	−5.6	−4.1	−5.5
MAX		26.8	30.5	10.2	16.8	15.1	14.4	15.8

The molecules are given in the protonated form. The proton affinity is computed with the potential energies at 0 K without any zero-point energy correction. For the DFTB methods the deviation is given as the difference to the G3B3 method (E^method – E^G3B3). The compilation of the molecules is taken from ref 39.

explanations see Table 1 and Table 2