Dielectric boundary conditions are omitted in these calculations. In Ref. 50, boundary conditions with ε = 4 increase ∆ ‡ E for model IV by 4.0 kcal/mol and increase ∆ rxn E by 5.6 kcal/mol. These corrections are similar for the smaller models, e.g., 3.9 kcal/mol (∆ ‡ E) and 2.7 kcal/mol (∆ rxn E) in the case of model III, and are only reduced below 1 kcal/mol for a larger model V with 220 atoms. In that case, values for both ∆ ‡ E and ∆ rxn E do converge (within 1 kcal/mol) for model V using fixed-atom constraints, but the present work suggests that convergence is more rapid when harmonic confining potentials are used instead.