FB-ENM/IDPP paths, however, cannot reproduce such a compact transition state structure. FB-ENM generates the shortest collision-free path, while IDPP uses linear interpolation of interatomic distances. Consequently, both methods yield a path where only the central hydrogen moves, with stationary outer hydrogens. The path midpoint becomes an energetically unstable structure with the central hydrogen dissociated from both outer hydrogens (Figure ). Notably, this structure differs from the actual transition state by over 70 kcal/mol, highlighting the significant limitation of FB-ENM/IDPP.