Critical Test of Some Computational Chemistry Methods
for Prediction of Gas-Phase Acidities and Basicities
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Abstract
Gas-phase
acidities and basicities were calculated for 64 neutral bases (covering
the scale from 139.9 kcal/mol to 251.9 kcal/mol) and 53 neutral acids
(covering the scale from 299.5 kcal/mol to 411.7 kcal/mol). The following
methods were used: AM1, PM3, PM6, PDDG, G2, G2MP2, G3, G3MP2, G4,
G4MP2, CBS-QB3, B1B95, B2PLYP, B2PLYPD, B3LYP, B3PW91, B97D, B98,
BLYP, BMK, BP86, CAM-B3LYP, HSEh1PBE, M06, M062X, M06HF, M06L, mPW2PLYP,
mPW2PLYPD, O3LYP, OLYP, PBE1PBE, PBEPBE, tHCTHhyb, TPSSh, VSXC, X3LYP.
The addition of the Grimmes empirical dispersion correction (D) to
B2PLYP and mPW2PLYP was evaluated, and it was found that adding this
correction gave more-accurate results when considering acidities.
Calculations with B3LYP, B97D, BLYP, B2PLYPD, and PBE1PBE methods
were carried out with five basis sets (6-311G**, 6-311+G**, TZVP,
cc-pVTZ, and aug-cc-pVTZ) to evaluate the effect of basis sets on
the accuracy of calculations. It was found that the best basis sets
when considering accuracy of results and needed time were 6-311+G**
and TZVP. Among semiempirical methods AM1 had the best ability to
reproduce experimental acidities and basicities (the mean absolute
error (mae) was 7.3 kcal/mol). Among DFT methods the best method considering
accuracy, robustness, and computation time was PBE1PBE/6-311+G** (mae
= 2.7 kcal/mol). Four Gaussian-type methods (G2, G2MP2, G4, and G4MP2)
gave similar results to each other (mae = 2.3 kcal/mol). Gaussian-type
methods are quite accurate, but their downside is the relatively long
computational time