Density Functional Theory (B3LYP-D3BJ/def2-TZVP) has RMSE > 9 kcal/mole before BAC. Middle: CBS-QB3, a composite method based on single-determinant wavefunctions, has RMSE close to 1 kcal/mole after BAC. Bottom: CCSD(T)-F12b, a high-level method involving explicit correlation between each pair of electrons, has RMSE < 2 kcal/mole even without BAC. See Ref. If one uses high-accuracy quantum chemistry methods, the computed rates using transition state theory often closely match experiments. One example is shown in Fig. , for the reaction phenyl + ethene. The effect of a 1 kcal/mole uncertainty in a reaction barrier height is also illustrated in Fig. : at high temperature it does not matter much, but at room temperature it leads to large uncertainty in k(T).