Applications of Time Dependent and Time Independent Density Functional Theory to the First 蟺 to 蟺* Transition in Cyanine Dyes

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• 作者：Hristina Zhekova ; Mykhaylo Krykunov ; Jochen Autschbach ; Tom Ziegler
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2014
• 出版时间：August 12, 2014
• 年：2014
• 卷：10
• 期：8
• 页码：3299-3307
• 全文大小：508K
• ISSN：1549-9626

文摘

The first 蟺 鈫?蟺* transition in a number of cyanine dyes was studied using both time dependent and time independent density functional methods using a coupled cluster (CC2) method as the benchmark scheme. On the basis of 10 different functionals, it was concluded that adiabatic time dependent density functional theory (ATDDFT) almost independently of the functional gives rise to a singlet鈥搕riplet separation that is too large by up to 1 eV, leading to too high singlet energies and too low triplet energies. This trend is even clearer when the Tamm鈥揇ancoff (TD) approximation is introduced and can in ATDDFT/TD be traced back to the representation of the singlet鈥搕riplet separation by a HF-type exchange integral between 蟺 and 蟺*. The time independent DFT methods (螖SCF and RSCF-CV-DFT) afford triplet energies that are functional independent and close to those obtained by ATDDFT. However, both the singlet energies and the singlet鈥搕riplet separations increases with the fraction 伪 of HF exchange. This trend can readily be explained in terms of the modest magnitude of a KS-exchange integral between 蟺 and 蟺* in comparison to the much larger HF-exchange integral. It was shown that a fraction 伪 of 0.5 affords good estimates of both the singlet energies and the singlet鈥搕riplet separations in comparison to several ab initio benchmarks.