In 2006, Leopoldini et al. investigated the spin-state dependence of possible reaction pathways in models for a nitrate reductase via separate FDE-type SCF calculations for singlet and triplet states . This is arguably the most straightforward type of application of ∆SCF, since no issues related to a possible collapse to the ground state occur because of different spin symmetry of the states involved. A study on the calculation of singlet-singlet excitation energies of a molecule in an environment that made use of FDE-∆SCF approaches was performed in a collaboration of our (JN's) lab with the Filippi group . There, however, the ∆SCF approach was only used to polarize the environment densities in a state-specific manner for subsequent use in WF-in-DFT calculations. In Ref. 266, FDE-∆SCF was employed to describe a local π → π * excitation in an ethene monomer in the presence of a second ethene molecule. The actual goal in that study was to employ the resulting orbitals for the definition of a diabatic state and the subsequent calculation of electronic coupling-matrix elements to a charge-transfer state (see also Sec. 6.3). One main advantage of ∆SCF-DFT over the corresponding linearresponse TDDFT approach is the easy availability of analytical gradients, which allows a straightforward application to excited-state dynamics. This route was followed in recent work by the Luber group to facilitate efficient non-adiabatic molecular dynamics of a diimide system in water .