Our CMS-PDFT calculations are unable to compute the energy at θ = 180 • due to the intermediate-state optimization not converging, so we omit this point and only consider θ between 135 • and 179 • . Figure shows the three excited singlet states for all the methods considered, with the zero of energy set to the first excited state at θ = 179 • . The upper states should become doubly degenerate 1 ∆ u states as θ → 180 • , and that is clearly seen for XMS-CASPT2 and XMS-PDFT, although the upper 1 ∆ u potential of XMS-PDFT has the wrong curvature around 160 • . The CMS-PDFT 1 ∆ u states, however, incorrectly remain split as θ → 180 • (Figure ). The ground-state potential curves are almost identical for all the methods except for CMS-PDFT, which has a discontinuity at θ = 179 • (Figure ).