Approximately Self-Consistent Ensemble Density Functional Theory With All Correlations

2020-05-29T12:32:01Z (GMT) by Tim Gould
The ability to predict low-lying excited states with the same ease as ground-states would represent a major advance in understanding interactions between light and chemistry, e.g. for solar cells or photocatalysis. Recent theory developments in ensemble density functional theory (EDFT) promise to bring decades of work for ground-states to the practical resolution of excited-state problem - provided newly-discovered "density-driven correlations" can be dealt with and adequate effective potentials can be found. This Letter introduces simple approximations to both the density-driven correlations and the potential; and shows that EDFT with the ωB97X density functional approximation outperforms ΔSCF DFT for singlet-triplet gaps in small atoms and molecules. It thus establishes EDFT as a vitally promising tool for low-cost but high-accuracy studies of excited states; and provides a clear route to practical EDFT implementation of arbitrary functional approximations.