(4.4.3) Gould : Much recent work on ensemble DFT (see Section 3.7) and DFAs is focused on excited states. Ensemble DFT has the useful feature that differentiation with respect to ensemble weights give access to Kohn-Sham wave functions (which can be multireference, 427 ) densities, and energies of excited states. It has already been shown that ensemble DFAs can outperform their DFT or TDDFT counterparts in some difficult cases. Moreover, ensemble DFT can do so without breaking any symmetries and thus preserves spectroscopic features such as degeneracies.