Moore Barry, Sun Haitao, Govind Niranjan, Kowalski Karol, Autschbach Jochen
Department of Chemistry, University at Buffalo, State University of New York, Buffalo , New York 14260-3000, United States.
State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University , Shanghai 200062, P. R. China.
J Chem Theory Comput. 2015 Jul 14;11(7):3305-20. doi: 10.1021/acs.jctc.5b00335. Epub 2015 Jun 17.
Criteria to assess charge-transfer (CT) and CT-like character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) calculations with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals are compared with coupled-cluster (CC) benchmarks. The test set comprises an organic CT complex, two push-pull donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT. It is shown that such CT-like excitations do not have the characteristics of physical charge transfer, and improvements with LC functionals may not be obtained for the right reasons. The TDDFT triplet excitation energies are underestimated for all systems, often severely. For the CT-like candidates, the singlet-triplet (S/T) separation changes from negative with a non-hybrid functional to positive with a tuned LC functional. For the cyanine, the S/T separation is systematically too large with TDDFT, leading to better error compensation for the singlet energy with a non-hybrid functional.
研究了评估电子激发的电荷转移（CT）和类CT特征的标准。将使用非杂化、杂化和调谐长程校正（LC）泛函的含时密度泛函理论（TDDFT）计算结果与耦合簇（CC）基准进行了比较。测试集包括一个有机CT配合物、两个推拉供体-受体发色团、一个花菁染料和几种多环芳烃。恰当的CT很容易识别。在空间接近区域内激发时密度发生显著变化的激发也可以被诊断出来。对于此类激发，在TDDFT中使用LC泛函有时会使单重态能量得到显著改善，类似于恰当的CT。结果表明，此类类CT激发不具有物理电荷转移的特征，并且使用LC泛函可能并非出于正确的原因而得到改善。对于所有体系，TDDFT计算得到的三重态激发能量都被低估，且常常被严重低估。对于类CT候选物，单重态-三重态（S/T）分离从使用非杂化泛函时的负值变为使用调谐LC泛函时的正值。对于花菁，TDDFT计算得到的S/T分离系统性地过大，导致使用非杂化泛函时单重态能量的误差补偿更好。
