Repeating the same systematic calculations with σ 2 -CASPT2, results in a smooth PEC with is sufficient to obtain a balanced first-order wave function throughout the dissociation, and remove all intruder states. However, a noticeable jump in the energy is present near the equilibrium distance. This discontinuity is due to two perturbers, whose denominators flip sign from R = 1.66 Å to R = 1.68 Å. As a result, a net change of about 0.04 eV in the correlation energy happens between these two points, despite avoiding the singularity at ∆ i = 0. This is the issue alluded to earlier in the theoretical discussion of the σ 1 regularizer, which limits its applicability to situations in which the molecular structure does not change.