Reaction pathways on the C 4 H 7 PES extracted by CTY from ReaxFF simulations are shown in Fig. . In total, 44 reactions of butenyl radicals, including the major isomerization and decompositions that are reported in the literature, were found within only ≈ 30 minutes wall-time. One shortcoming of the ReaxFF parametrization can be seen from e.g. the left and right ends of Fig. : the sum of energies of decomposition products is often higher than the TS connecting them. In principle, such submerged barriers may exist, but in these cases this is owed to the ReaxFF parametrization badly reproducing the energy of the system (similar issues may arise for B3LYP barrier optimizations). Nevertheless, the obtained pathways can be validated and the resulting geometries of TSs and products are descriptive starting points for higher-level optimizations. The inset of Fig. shows the comparison of the TS geometry extracted by CTY at the ReaxFF level and the geometry optimized at QCISD/6-311++G(2df,2p) level from the literature. 48 The dierence in bond lengths amounts to 10 % to 30 %, but the TS features are well captured and good enough to serve as an initial geometry guess for high-level quantum chemical calculation for both β-scission and isomerization PESmapping, and two more pathways show up in the simulations, cf. Fig. .