Ensemble density functional theory of ground and excited energy levels

Emmanuel Fromager

doi:10.1021/acs.jpca.4c06744

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arXiv · 2409.17000

Ensemble density functional theory of ground and excited energy levels

Emmanuel Fromager

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Abstract

A Kohn-Sham density-functional energy expression is derived for any (ground or excited) state within a given many-electron ensemble along with the stationarity condition it fulfills with respect to the ensemble density, thus giving access to both physical energy levels and individual-state densities, in principle exactly. We also provide working equations for the evaluation of the latter from the true static ensemble density-density linear response function. Unlike in Gould's recent ensemble potential functional approach to excited states [arXiv:2404.12593], we use the ensemble density as sole basic variable. While a state-specific KS potential naturally emerges from the present formalism, at the exact ensemble Hartree-exchange-only (Hx) level of approximation, the standard implementation of orbital-optimized DFT for excited states is recovered when recycling the regular ground-state Hx-correlation functional in this context.

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Emmanuel Fromager. 2024-09-25. Ensemble density functional theory of ground and excited energy levels. https://doi.org/10.1021/acs.jpca.4c06744

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