Accurate double excitations from ensemble density functional calculations

Francisca Sagredo; Kieron Burke

doi:10.1063/1.5043411

Accurate double excitations from ensemble density functional calculations

J Chem Phys. 2018 Oct 7;149(13):134103. doi: 10.1063/1.5043411.

Authors

Francisca Sagredo¹, Kieron Burke¹

Affiliation

¹ Department of Chemistry, University of California, Irvine, California 92697, USA.

PMID: 30292227
DOI: 10.1063/1.5043411

Abstract

The recent use of a new ensemble in density functional theory (DFT) to produce direct corrections to the Kohn-Sham transitions yields the elusive double excitations that are missed by time-dependent DFT (TDDFT) with the standard adiabatic approximation. But accuracies are lower than for single excitations, and formal arguments about TDDFT suggest that a correction kernel is needed. In principle, ensemble DFT with direct corrections at the exchange level must yield accurate doubles in the weakly correlated limit. We illustrate with exact calculations and analytic results on the Hubbard dimer. We also explain the error in formal arguments in TDDFT.