The popular low-level DFT method B3LYP-D3BJ, green bars in top figure, mis-predicts many molecules' enthalpies by more than 10 kcal/mole, much larger than RT, corresponding to errors of many orders of magnitude in Keq's and k's. Fitted bond-additivity corrections (BAC), using the form proposed by Anantharaman and Melius , help significantly (purple bars) but even after these tweaks are there are still many errors ~3 kcal/mole or larger. The intermediate-level method CBS-QB3, middle, has been very popular in the combustion/pyrolysis community over the past two decades, since with BAC (purple histogram) it predicts most enthalpies within 2 kcal/mole, without requiring too many computational resources for molecules containing up to about 12 carbon atoms. Note RT > 2 kcal/mole if T>1000 K. The highest-level method shown in Fig. , DLPNO-CCSD(T)-F12b/cc-pCVTZ-F12//ωB97M-V/def2-TZVPD, bottom, is so accurate that it does not require BAC corrections to predict almost all of the enthalpies within 2 kcal/mole, green bars. If BAC are applied to this method, most of the enthalpy errors drop to less than 1 kcal/mole, corresponding to about a factor of 3 uncertainty in Keq's at 500 K. For further discussion of methodology and similar tests of other quantum chemistry methods see . Several research groups have automated quantum calculations of thermochemistry to automatically update the thermochemical parameters for hundreds of species in kinetic models. Note that errors in energies are more tolerable at high temperatures, where RT is larger, than at low temperatures. At present we often can predict k's and Keq's fairly accurately at combustion temperatures, because we have methods that can predict energies with errors <RTcombustion. But predicting accurate k's and Keq's at room temperature is difficult, because most methods cannot compute energies with errors <RTroom. Much of the most interesting low-temperature chemistry occurs in solvents, making it even more challenging to compute the energies to high accuracy. COSMO-RS calculations based on DFT charge distributions predict the solvent corrections to the thermochemistry for many small neutral molecules in normal solvents with errors of about 1 kcal/mole , an error that adds to the often larger errors in the quantum chemistry prediction of the gas-phase enthalpies of formation. Errors in both types of calculations need to be reduced to enable accurate predictions of kinetics at room temperature.