In the cartesian case one can easily encounter overlapping atoms as the algorithm cannot distinguish bonded from non-bonded atoms. In the case of R7 and R8 the Z-matrix interpolation is in fact very close to the converged final pathway. This stark difference in performance relative to the other reactions is easily explained by the type of pathways being computed. The atomic movements for R7 and R8 in the converged MEP are dominated by angular motions, which are very hard to describe in cartesian space. The IDPP method primarily avoids atom overlaps, but the initial guess is still built in cartesian coordinates, leading to a slow convergence for these two particular cases."