The optimal choice of interpolation method will, of course, strongly vary on the reaction under study. Some paths will be easier to represent in cartesian space (such as the carbocation reactions R4-R5), others are more assessible with an adequate selection of internal coordinates. As previously noted, there were three sets of initial pathways: simple cartesian space In order to keep the figure easily readable, we set as maximum threshold for optimisation 400 iterations. interpolation (Cartesian), the same definition as in the latter case but with a preoptimisation of the path with IDPP (Cartesian+IDPP) and finally with our own Z-matrix definition (Internal). The number of individual optimisation steps (gradient+energy calculations) required to converge the NEB paths in dependence of the method used for the initial pathway are provided in Figure . In some cases convergence could not be achieved when setting the limit to 400 individual steps. For many reactions, the performance of cartesian and internal coordinates is rather similar. It should be noted, nonetheless, that there is not a single reaction whereby the cartesian coordinate interpolation is superior (less iterations). The use of IDPP closes the gap rather efficiently, producing numbers very close or even lower than the internal coordinates result (4 out of 8). The most noticeable differences are observed in reactions whereby fragments (or whole molecules) are displaced in cartesian space without great changes to their internal structure. This is the case for the water dimer and the two reactions involving the methanol-furan dimer (Mefur), whereby cartesian coordinates produce a nonsensical interpolation. The reason for this difference is visible when comparing the initial paths from both sets (see Figures and).