Excitation energies from state-specific ensemble density functionals with density-driven correlations

We present an effective ensemble density functional approximation, which we call GX24 as it is suitable for both ground (G) and excited state (X) energy prediction. This functional is derived from first principles based on a novel approximation for density-driven correlations. We show that GX24 exploits recent advances in ensemble density functional theory to resolve major paradigmatic failures (double excitations, charge transfer) of standard time-dependent density functional approximations. It thus represents a major step toward accurate modelling of neutral and charged excitations in a unified fashion.