We attribute PM6's high accuracy to its parametrization with CC energy data of its non-covalent interactions. The energy deviations of DFT calculations, that is PBE, PBE0 and LC-PBE are -29.9, -19.1, and -10.1 kJ•mol -1 , respectively. This energy trend follows the Jacob's ladder principle by which a more precise treatment of the exchange-correlation term enhances the prediction of the electronic energy. However, none of the activation energies calculated with these methods are within the chemical accuracy range of ±4.18 kJ•mol -1 . The poor accuracy of TS energy calculations with DFT functionals in this type of reactivity agrees with a previous benchmark study. Only data obtained from DLPNO and canonical CC resulted in reliable TS activation energies, as depicted with a green rectangle in Figure . Despite the fact that DLPNO is an approximation of the canonical CC, the former demonstrates a similar accuracy to the latter, even when pvtz CCSD(T) is approximately three times slower than pvtz DLPNO-CCSD(T) (Figure ). In fact, the wall clock time of the canonical CC rapidly scales exponentially for molecules with more than 20 atoms, whereas DLPNO CC scales linearly even with molecules up to 1000 atoms. Moreover, complete basis set extrapolations (CBS) shows a higher deviation than the triple and quadruple zeta basis sets. Data in Figure also illustrates that pvqz DLPNO-CCSD(T) is 4.1 times more accurate than pvtz DLPNO-CCSD(T), however, it is also 4.7 times more expensive.