It is noted that the interpolating methods do not guarantee performance in regions that are lacking data points. Thus, a large number of configurations should be sampled to cover all dynamically related regions for developing a full-dimensional PES of a chemical system. Their electronic energies are required to be computed by a suitable electronic structure method, which can be single-or multi-reference wavefunction methods. Note that most sampled points are far away from the equilibrium of the stationary points and may encounter the convergence issue in the HF step, particularly for regions of multireference nature, such as bond-breaking regions. Even successfully converged, the HF calculation may converge to a wrong state and the resulting energies might be not consistent. Multi-reference methods become the natural choice. As pointed out by Dawes and Ndengué in their review paper, "in a multireference PES, an inconsistency in a preliminary HF calculation may not be reflected in the final MRCI energy, as long as the CASSCF reference 'recovers' and converges correctly." Existing example PESs based on MRCI or CASPT2 calculations include HO2, 85 O3, F/Cl + H2O, , N4, OH + O2, 88 CH4, etc.