Analytic energy gradients of spin-adapted open-shell time-dependent density functional theory

Zikuan Wang; Zhendong Li; Yong Zhang; Wenjian Liu

doi:10.1063/5.0025428

Analytic energy gradients of spin-adapted open-shell time-dependent density functional theory

J Chem Phys. 2020 Oct 28;153(16):164109. doi: 10.1063/5.0025428.

Authors

Zikuan Wang¹, Zhendong Li², Yong Zhang³, Wenjian Liu³

Affiliations

¹ Beijing National Laboratory for Molecular Sciences, Institute of Theoretical and Computational Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People's Republic of China.
² Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China.
³ Qingdao Institute for Theoretical and Computational Sciences, Shandong University, Qingdao, Shandong 266237, People's Republic of China.

PMID: 33138406
DOI: 10.1063/5.0025428

Abstract

It is now well established that the spin-adapted time-dependent density functional theory [X-TD-DFT; Li and Liu, J. Chem. Phys. 135, 194106 (2011)] for low-lying excited states of open-shell systems has very much the same accuracy as the conventional TD-DFT for low-lying excited states of closed-shell systems. In particular, this has been achieved without computational overhead over the unrestricted TD-DFT (U-TD-DFT) that usually produces heavily spin-contaminated excited states. It is shown here that the analytic energy gradients of X-TD-DFT can be obtained by just slight modifications of those of U-TD-DFT running with restricted open-shell Kohn-Sham orbitals. As such, X-TD-DFT also has no overhead over U-TD-DFT in the calculation of energy gradients of excited states of open-shell systems. Although only a few prototypical open-shell molecules are considered as showcases, it can definitely be said that X-TD-DFT can replace U-TD-DFT for geometry optimization and dynamics simulation of excited states of open-shell systems.