That is the good news, and it has made LR-TDDFT absolutely ubiquitous for the calculation of vertical excitation spectra. The bad news, from the standpoint of photochemical investigations, is that the topology of any CX that involves the ground state is fundamentally flawed in LR-TDDFT, with seams that are (N int -1)-dimensional rather that (N int -2)-dimensional. This can be seen clearly from the LR-TDDFT potential energy surfaces for ethylene that are plotted in Fig. , around the same two geometries used to generate the plots in Fig. . Using LR-TDDFT, no intersection with the correct topology can be found. Numerical values of the tilt parameters in Eq. ( ) also fail to correlate with the observed potential energy landscape. This incorrect behavior originates in a lack of proper coupling between the ground (reference) state and the response (excited) states. At some level, this is a problem with response theory rather than with TDDFT per se, and from a different point of view the issue is that LR-TDDFT affords an unbalanced treatment of ground versus excited states. The ground state is variationally optimized via solution of the Kohn-Sham equations but then the excited states are obtained from a separate eigenvalue problem, and therefore do not satisfy a variational principle with respect to the ground state. (The excited states are, however, variational with respect to one another. As a result, CXs between two excited states are free of the aforementioned topology problems.) The predicament is brought to the forefront by Jahn-Teller problems involving symmetry-required degeneracy of the ground state, and the simplest such example is the H 3 radical in its D 3h geometry. As a result of the unbalanced manner in which ground and excited states are described, conventional LR-TDDFT struggles to describe the degeneracy, as can be seen clearly in Fig. . To emphasize that this is not a DFT problem per se, Fig. shows that the configuration interaction singles (CIS) method 13 also struggles, even in a restricted open-shell formulation.