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KMID : 1059520190630020073
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Journal of the Korean Chemical Society
2019 Volume.63 No. 2 p.73 ~ p.77
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A Comparison of the Density Functional Theory Based Methodologies for the Triplet Excited State of π-Conjugated Molecules: Time-Dependent DFT (TD-DFT), TD-DFT within Tamm-Dancoff Approximation (TDA-DFT), and Spin-Unrestricted DFT (UDFT)
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Ahn Chang-Hwan
Kim Dong-Wook
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Abstract
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We compared methodologies based on the density functional theory (DFT), e.g., time-dependent DFT (TD-DFT), TD-DFT within Tamm-Dancoff approximation (TDA-DFT), and spin-unrestricted DFT (UDFT), that are usually employed to optimize the geometries of π-conjugated molecules in their lowest lying triplet excited (T1) state. As a model system for π-conjugated molecules, we employed 1,2,3,4,5-pentacyano-6-phenyl-benzene. In conjunction with 6-31G(d) basis sets, we made use of gap-tuned range-separated ωB97X functional which is often employed recently in the calculations of molecular excited states. Near the equilibrium geometries, we found that the important difference between the geometries derived at UDFT level and those at TD-DFT or TDA-DFT methods: more stable ground-state energies but higher triplet excitation energies for UDFT derived geometries. In the studies, we discuss such differences in more detail.
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KEYWORD
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π-Conjugated molecule, Triplet excited state, DFT calcul
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