Excitation Energies from Thermally-Assisted-Occupation Density Functional Theory: Theory and Computational Implementation

• URL: http://arxiv.org/abs/2007.07590v2
• Date: Fri, 14 Aug 2020 06:45:32 GMT
• Title: Excitation Energies from Thermally-Assisted-Occupation Density Functional Theory: Theory and Computational Implementation
• Authors: Shu-Hao Yeh, Aaditya Manjanath, Yuan-Chung Cheng, Jeng-Da Chai, and Chao-Ping Hsu
• Abstract summary: We develop time-dependent (TD) TAO-DFT, which is a time-dependent, linear-response theory for excited states. TDTAO-DFT also yields zero singlet-triplet gap in the dissociation limit, for the ground singlet ($11Sigma_g+$) and the first triplet state ($13Sigma_u+$)
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-sa/4.0/
• Abstract: The time-dependent density functional theory (TDDFT) has been broadly used to investigate the excited-state properties of various molecular systems. However, the current TDDFT heavily relies on outcomes from the corresponding ground-state density functional theory (DFT) calculations which may be prone to errors due to the lack of proper treatment in the non-dynamical correlation effects. Recently, thermally-assisted-occupation density functional theory (TAO-DFT) [J.-D. Chai, \textit{J. Chem. Phys.} \textbf{136}, 154104 (2012)], a DFT with fractional orbital occupations, was proposed, explicitly incorporating the non-dynamical correlation effects in the ground-state calculations with low computational complexity. In this work, we develop time-dependent (TD) TAO-DFT, which is a time-dependent, linear-response theory for excited states within the framework of TAO-DFT. With tests on the excited states of H$_{2}$, the first triplet excited state ($1^3\Sigma_u^+$) was described well, with non-imaginary excitation energies. TDTAO-DFT also yields zero singlet-triplet gap in the dissociation limit, for the ground singlet ($1^1\Sigma_g^+$) and the first triplet state ($1^3\Sigma_u^+$). In addition, as compared to traditional TDDFT, the overall excited-state potential energy surfaces obtained from TDTAO-DFT are generally improved and better agree with results from the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD).

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