ReaxFF training procedure requires three different inputs: i) geometries, a set of atom clusters crucial in describing the system of interest (e.g., bond stretching, angle and torsion scans, reaction transition states, crystal structures, etc.), ii) training data, properties of these atom clusters (such as energy minimized structures, relative energies for bond/angle/torsion scans, partial charges and forces) calculated using high-fidelity QM models, iii) model parameters to be optimized along with a fitness function that combines different types of training items as follows: