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) 


Vol. 63,  No. 2, pp. 73-77, Apr.  2019
10.5012/jkcs.2019.63.2.73


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  Abstract

π-공액계 분자에 대해, density functional theory (DFT) 방법에 기반한 일반적인 삼중항 구조 최적화 방법들, 즉, 시간 의 존적 DFT (TD-DFT), Tamm-Dancoff 근사법에 기반한 TD-DFT (TDA-DFT), 그리고 스핀-비제한 DFT (UDFT)에 대한 점검을 수 행하였다. 모델 분자로서 1,2,3,4,5-pentacyano-6-phenyl-benzene가 이용되었고, 6-31G(d) 기저 함수와 더불어 여기 상태 계산에 최 근 자주 사용되는 에너지 차 조정 영역 분리 functional인 ωB97X functional이 사용되었다. 계산 결과 평형 구조 근처에서, UDFT 최적화된 구조는 TD-DFT 및 TDA-DFT 계산 구조와는 다른 차이점을 보인다. 즉, 보다 안정한 바닥 상태 에너지와 보다 높은 삼 중항 여기 에너지가 UDFT 최적화 구조에서 보인다. 본 논문에서는 이러한 차이에 대해 보다 자세히 토의된다. 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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  Cite this article

[IEEE Style]

C. H. Ahn and D. Kim, "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)," Journal of the Korean Chemical Society, vol. 63, no. 2, pp. 73-77, 2019. DOI: 10.5012/jkcs.2019.63.2.73.

[ACM Style]

Chang Hwan Ahn and Dongwook Kim. 2019. 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). Journal of the Korean Chemical Society, 63, 2, (2019), 73-77. DOI: 10.5012/jkcs.2019.63.2.73.

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ISSN(Print) 1017-2548
ISSN(Online) 2234-8530