3. Evaluation through PES explorations: Conduct potential energy scans at the QM/MM level along the reaction coordinate using the re-parametrized Hamiltonian. This step ensures that the modified parameters provide a reasonable description of the entire reaction path, rather than just isolated geometries. New single-point calculations at the QM/MM level using the chosen HL method on semiempirical geometries can be performed to assess performance of the re-parametrized Hamiltonian. The new data from this step may be incorporated into the fitting process if significant deviations are observed.