The TD-ADGA settings and thresholds used in the simulations are listed in Tab. 1 and they have been described in Section 2. Unless otherwise stated, the epsilon thresholds used in the TD-ADGA calculations are the same as those which have been used in the TI-ADGA calculations to obtain the reference PESs, with the exception of the linear threshold which is not used in the TI-ADGA. The number of grid points which the density is smoothened over (N q ) is given as a fraction of the grid size (c q ) such that the number of grid points to smoothen over is given as N q = c q N pts , where N pts is the total number of grid points in a one-mode cut.