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. 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 9.

Proton Transfer Barrier in kcal/mol for a Fixed Distance (rXY) between the Heavy Atoms (X,Y∈{O,N}): Deviation of DFTB and DFT in Comparison to MP2/G3largea

barrier rXY MP2 DFTB2 DFTB3-diagb DFTB3b PBEc B3LYPc
calc fit calc fit
[H2O-H-H2O]+ 2.5 0.6 −0.6 −0.6 −0.6 −0.6 −0.6 −0.5 −0.4
2.6 2.4 −1.4 −0.2 +0.0 −1.1 −0.8 −1.9 −1.0
2.7 5.2 −1.1 +0.5 +0.8 −0.7 −0.3 −3.2 −1.5
2.8 8.9 −1.3 +0.5 +0.9 −0.9 −0.4 −4.4 −1.9
[OH-H-OH]− 2.5 0.5 −0.5 −0.5 −0.5 −0.5 −0.5 −0.5 −0.2
2.6 2.3 −2.3 −0.6 −0.2 −0.7 +0.0 −1.6 −0.6
2.7 5.2 −4.6 −0.0 +0.5 −0.2 +0.9 −2.7 −0.9
2.8 8.8 −6.7 −0.0 +0.7 −0.3 +1.2 −3.7 −1.2
[NH3-H-NH3]+ 2.6 0.4 −0.4 −0.4 −0.4 −0.4 −0.4 −0.4 −0.3
2.7 1.9 −1.8 −1.0 −1.4 −1.7 −1.7 −1.9 −1.0
2.8 4.4 −2.4 −0.5 −1.4 −2.0 −2.2 −3.0 −1.6
2.9 7.7 −2.5 −0.1 −1.2 −2.1 −2.2 −4.1 −2.2
[NH2-H-NH2]− 2.5 0.1 −0.0 +0.3 −0.1 −0.1 −0.1 +0.0 +0.0
2.6 1.4 −1.4 +5.2 −1.1 −0.4 −1.0 −1.2 −0.5
2.7 3.5 −3.5 +5.5 −0.6 +1.5 −0.5 −2.1 −0.8
2.8 6.3 −4.9 +6.9 +0.6 +2.9 +0.9 −3.0 −1.1
[NH3-H-H2O]+ d 2.9 25.3 −8.2 −5.2 −4.2 −5.8 −5.3 -e −2.7
3.0 30.0 −9.5 −6.3 −5.4 −7.3 −6.7 −6.8 −3.3
3.1 35.1 −11.0 −7.7 −6.8 −8.9 −8.2 −7.8 −3.8
3.2 40.5 −12.5 −9.1 −8.2 −10.5 −9.8 −8.8 −4.2
[H2O-H-NH3]+ d 2.9 0.8 +0.7 +2.2 +1.1 +0.2 +0.1 -e −0.8
3.0 3.3 +0.9 +2.9 +1.5 +0.2 +0.1 −3.0 −1.6
3.1 6.7 +0.3 +2.3 +0.9 −0.6 −0.7 −4.5 −2.3
3.2 10.7 −0.8 +1.3 −0.2 −1.9 −2.0 −5.9 −2.9
[NH2-H-OH]− d 2.8 10.1 −6.3 −4.6 +2.4 −2.5 +2.9 −3.3 −0.8
2.9 14.2 −8.6 −5.2 +2.1 −3.1 +2.7 −4.2 −1.1
3.0 18.6 −11.1 −6.0 +1.4 −3.9 +2.1 −5.1 −1.4
3.1 23.3 −13.4 −6.7 +0.7 −4.7 +1.5 −5.9 −1.6
[OH-H-NH2]− d 2.8 4.4 −4.1 +14.4 +0.3 +6.6 +0.7 −2.8 −1.2
2.9 7.8 −5.2 +15.8 +1.1 +7.9 +1.6 −4.0 −1.7
3.0 11.6 −6.6 +16.5 +1.2 +8.4 +1.7 −4.9 −2.0
3.1 15.8 −8.8 +16.2 +0.1 +7.8 +0.7 −5.8 −2.3
a

Barriers are computed as described in the text at 0 K and no zero-point energy correction has been included. For the DFT and DFTB methods the deviation is given as the difference to the MP2 method (Emethod – EMP2). For all models the NHorg parameter set is applied.

b

explanations see Table 1 and Table 2

c

Basis set 6-31+G(d,p)

d

Barrier in comparison to the relaxed structure with the proton binding to the heavy atom that is written on the left hand side of that proton.

e

a barrier does not exist