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Ensemble density functional theory extends the usual Kohn-Sham machinery toquantum state ensembles involving ground- and excited states. Recent work bythe authors [Phys. Rev. Lett. 119, 243001 (2017); 123, 016401 (2019)] has shownthat both the Hartree-exchange and correlation energies can attain unusualfeatures in ensembles. Density-driven(DD) correlations -- which account for thefact that pure-state densities in Kohn-Sham ensembles do not necessarilyreproduce those of interacting pure states -- are one such feature. Here westudy atoms (specifically $S$--$P$ and $S$--$S$ transitions) and show that themagnitude and behaviour of DD correlations can vary greatly with the variationof the orbital angular momentum of the involved states. Such estimations areobtained through an approximation for DD correlations built from relevant exactconditions Kohn-Sham inversion, and plausible assumptions for weakly correlatedsystems.

Density driven correlations in ensemble density functional theory: insights from simple excitations in atoms