  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.
