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Computation 2017, 5(1), 9;

Excitons in Solids from Time-Dependent Density-Functional Theory: Assessing the Tamm-Dancoff Approximation

Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
Author to whom correspondence should be addressed.
Academic Editor: Jianmin Tao
Received: 21 December 2016 / Revised: 21 January 2017 / Accepted: 23 January 2017 / Published: 29 January 2017
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Excitonic effects in solids can be calculated using the Bethe-Salpeter equation (BSE) or the Casida equation of time-dependent density-functional theory (TDDFT). In both methods, the Tamm-Dancoff approximation (TDA), which decouples excitations and de-excitations, is widely used to reduce computational cost. Here, we study the effect of the TDA on exciton binding energies of solids obtained from the Casida equation using long-range-corrected (LRC) exchange-correlation kernels. We find that the TDA underestimates TDDFT-LRC exciton binding energies of semiconductors slightly, but those of insulators significantly (i.e., by more than 100%), and thus it is essential to solve the full Casida equation to describe strongly bound excitons. These findings are relevant in the ongoing search for accurate and efficient TDDFT approaches for excitons. View Full-Text
Keywords: excitons; time-dependent density-functional theory; Tamm-Dancoff approximation excitons; time-dependent density-functional theory; Tamm-Dancoff approximation

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Byun, Y.-M.; Ullrich, C.A. Excitons in Solids from Time-Dependent Density-Functional Theory: Assessing the Tamm-Dancoff Approximation. Computation 2017, 5, 9.

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