Several factors may contribute to the CNEO-TST overestimation. First, it is known that TST without optimizing the transition state location may overestimate rate constants at higher temperatures due to the neglect of recrossing effects. Second, the CMES employed here corresponds to a quantum calculation only for the ground vibrational state, so the CNEO effective PES is a low-temperature effective PES and, in an ideal scenario, a zero-temperature effective PES if electron-nuclear correlation effects could be fully accounted for. The more approximate nature of the vibrational treatment for excited vibrational states may be a cause of larger error at high temperature. Third, due to the DFT treatment, inevitable errors may persist in both electronic and nuclear energies, which are concealed within the total CNEO energy in all calculations. Evaluating the magnitudes of these errors requires systematic benchmark work, and further investigations of these factors are beyond the scope of the present paper. As a preliminary test of the neglect of electron-proton correlation, we have performed calculations with the electron-proton correlation functional epc17-2, 128 and the results are also presented in Figure . With the epc17-2 functional, CNEO-TST provides rate constants similar to those without electron-proton correlation, although some of the details, such as the quantitative accuracy of the zero-point energies, do change. 128 However, since the epc17-2