Ensemble Time-Dependent Density Functional Theory

Kimberly J. Daas; Steven Crisostomo; Kieron Burke

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arXiv · 2507.19464

Ensemble Time-Dependent Density Functional Theory

Kimberly J. Daas·Steven Crisostomo·Kieron Burke

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Abstract

Time-dependent density functional theory (TDDFT) is a standard approach for calculating optical excitations of molecules and solids, while ensemble DFT (EDFT) is a promising alternative under development. We introduce ensemble TDDFT (ETDDFT), a practical theory that combines the two, generalizing both; we ensemble-generalize the Gross-Kohn equation and the exchange-correlation kernel of TDDFT, and generalize EDFT to time-dependent problems. We relate coordinate scaling to the adiabatic connection. The new theory provides multiple avenues for constructing and using approximations. We illustrate these on the 2-site Hubbard model. We connect our results to the more general case of non-perturbative time-dependence.

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Kimberly J. Daas, Steven Crisostomo, Kieron Burke. 2025-07-25. Ensemble Time-Dependent Density Functional Theory. https://arxiv.org/abs/2507.19464

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