To obtain the reference PES, we carried out a TI-ADGA calculation using an average VSCF density obtained from the eight lowest energy modals in the TS mode and the four lowest energy states in the remaining five modals of the system. Further, we did not use the default threshold for the relative convergence threshold (ε rel = 1.0 • 10 -2 ) but a tighter value of 1.0 • 10 -3 in order to get an accurate representation of the PES. To obtain this PES the TI-ADGA requested a total of 45787 SPs.