Density functional calculations of E2 and S_N2 reactions: Effects of the choice of density functional, basis set, and self-consistent iterations

We have computed stationary points on the potential energy surface for the anti-E2, syn-E2, and S_N2 pathways of the reactions of F^- and Cl^- with CH₃CH₂F and CH₃CH ₂Cl with fully self-consistent fields and Gaussian basis functions. We find large differences from previously reported [Bento, A. P.; Solà, M.; Bickelhaupt, F. M. J. Chem. Theory Comput. 2008, 4, 929] calculations with Slater-type orbitals. We revise the findings of the previous study; in particular, we find average absolute errors in kcal/mol compared to benchmark calculations of 20 stationary point energies (6 saddle points and 14 minima) of 0.9 for M06-2X, 1.2 for M08-SO, 1.4 for M06-HF, 2.0 for M06, 2.3 for B3LYP, 2.5 for OLYP, 2.7 for M06-L, and 3.5 kcal/mol for TPSS. We also compare the predictions of various density functionals for the partial atomic charges at the transition states.