IDPP-based path generation yields excellent results for simple systems. However, as the transformation from reactant to product becomes complex, paths passing through highenergy regions often arise. Four possible factors are highlighted below. First, constraints are imposed on all atom pairs. As mentioned above, since the total number of atom pairs exceeds the system's degrees of freedom, structures satisfying |r ij | = d ij (α) for all pairs generally do not exist. In this case, the unresolvable constraint/frustration may appear as undesired distortions in the molecular structure. Second, interatomic distances are linearly interpolated. This naive interpolation between the reactant and product based on the internal coordinates of interatomic distances does not guarantee any steric preferability of the reaction path. Rather, it may provide a sterically unfavorable path, leading to undesired molecular distortions. Third, due to the weight function w(r) = r -4 , each pair potential v(r; d) decreases for r > 2d, meaning that structures with long interatomic distances can be stabilized. In fact, undesired bond breaking frequently occurs in path generation using IDPP. Fourth, each pair potential v(r; d) diverges at r = 0. The strong repulsive force near r = 0 can cause the optimization calculation to fail, and even if it does not fail, it can trigger the interatomic distances to be pushed into the r > 2d region.