(1) The reaction profile is primarily characterized by exploring the reactants, products, intermediates, and transition states connecting them. The reaction F + H2O → HF + OH is exothermic, -17.61 kcal/mol, with a barrier height of 1.93 kcal/mol. Other channels, such as HOF + H (89.9 kcal/mol) and FO + H2 (87.1 kcal/mol), were too high in energy to be included in the sampling. (2) Regions around the stationary points and along the minimum energy paths are carefully sampled. The energies, geometries, harmonic frequencies of the stationary points, and the potentials along the MEPs should be well sampled. As shown in the inset of Figure , the potential along the MEP of the OH + HO2 → H2O + O2 reaction is well reproduced by the PES, compared to the CCSD(T)-F12a/AVTZ calculations. Other important and useful one-dimensional scans, such as approaching between reactants or products at various directions, are included.