Along these lines, two recent TSH studies have made a side-by-side comparison of S 1 lifetimes predicted by LR-versus SF-TDDFT. Zhu and co-workers 29 examined cis → trans photoisomerization of azobenzene and found little difference between either the predicted S 1 lifetime or the branching ratio between cis and trans photoproducts, at odds with the notion that topology of the S 0 /S 1 CX should lead to differences in measurable observables. It is certainly true that most nonadiabatic transitions happen near rather than at a CX, if only because the volume of configuration space is much larger if one admits quasi-degenerate geometries. It is therefore possible that in some cases the topological details may have no observable impact on the outcome of a particular photochemical reaction. A contrasting example, however, comes from a recent TSH study of the trans → cis photoisomerization of the protonated Schiff base C 5 H 6 NH + 2 , for which LR-and SF-TDDFT methods predict significantly different S 1 lifetimes. The lifetime predicted using SF-TDDFT agrees with that obtained in CASPT2-based TSH simulations, whereas the LR-TDDFT lifetime is much longer. The reason is that topological problems in LR-TDDFT warp the S 1 potential surface in the vicinity of the photochemically-relevant S 0 /S 1 intersection, leading to the presence of a barrier that is not present in either the SF-TDDFT calculations or the multireference benchmarks. LR-TDDFT's topology problem thus manifests as a topography problem, and trapping behind an artificial barrier leads to slower dynamics. Such problems appear to manifest in some but not all cases, e.g., LR-TDDFT potential energy surfaces for CH 2 NH + 2 are reported to be in good agreement with multireference results in the region of an S 0 /S 1 intersection. Results for C 5 H 6 NH + 2 as well as theoretical considerations, however, demonstrate that there is a potential for serious problems.