Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline
Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline
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DOI：
10.1080/00268976.2013.793841
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发表时间：
2013-07-01
影响因子：
1.7
通讯作者：
Kongsted, Jacob
中科院分区：
文献类型：
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作者：
Eriksen, Janus J.;Sauer, Stephan P. A.;Kongsted, Jacob
我们研究了含时密度泛函理论（TDDFT）中CAM-B3 LYP交换相关（xc）泛函与极化嵌入（PE）方案耦合的失效问题用PE-CAM-B3 LYP方法模拟了对硝基苯胺（pNA）在水溶液中最低强度电荷转移激发的溶致变色位移，并与耦合团簇单分子和双分子（CCSD）方法的结果进行了比较模型还耦合到极化嵌入方案（PE-CCSD）。我们确定在地面和激发电荷转移状态的电荷分离量与这两种方法通过计算在气相中的电偶极矩和100溶剂配置。我们发现CAM-B3 LYP高估了基态固有的电荷分离量，TDDFT/CAM-B3 LYP大大低估了激发电荷转移态的电荷分离量。由于溶剂化色移中的误差被发现是成反比的偶极矩激发时的变化，我们的结论是，在描述的溶剂化色移的这种激发的缺陷是与TDDFT本身，以及它如何响应溶剂效应建模的PE计划。因此，我们建议TDDFT计算的基准结果与CAM-B3 LYP的分子内电荷转移激发在分子系统中类似于pNA对更高级别的从头算波函数方法，如，例如CCSD，在使用之前。使用计算得到的偶极矩变化作为电荷转移特性的测量值，我们进一步证实了用TDDFT和Tamm-Dancoff近似（TDA）TDDFT计算得到的激发能之间的差异确实与真空和溶液中给定电子跃迁的电荷转移特性相关。这是由相应的偶极矩的变化和所调查的CT激励的指数诊断的大小之间的相关性支持。
We investigate the failure of time-dependent density functional theory (TDDFT) with the CAM-B3LYP exchange-correlation (xc) functional coupled to the polarisable embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge-transfer excitation in para-nitroaniline (pNA) in water by comparing with results obtained with the coupled cluster singles and doubles (CCSD) model also coupled to the polarisable embedding scheme (PE-CCSD). We determine the amount of charge separation in the ground and excited charge-transfer state with both methods by calculating the electric dipole moments in the gas phase and for 100 solvent configurations. We find that CAM-B3LYP overestimates the amount of charge separation inherent in the ground state and TDDFT/CAM-B3LYP drastically underestimates this amount in the excited charge-transfer state. As the errors in the solvatochromatic shift are found to be inverse proportional to the change in dipole moment upon excitation, we conclude that the flaws in the description of the solvatochromic shift of this excitation are related to TDDFT itself and how it responds to the solvent effects modelled by the PE scheme. We recommend therefore to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge-transfer excitations in molecular systems similar to pNA against higher level ab initio wave function methods, like, e.g. CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a measure for charge-transfer character, we furthermore confirm that the difference between excitation energies calculated with TDDFT and with the Tamm-Dancoff approximation (TDA) to TDDFT is indeed correlated with the charge-transfer character of a given electronic transition both in vacuo and in solution. This is supported by a corresponding correlation between the change in dipole moment and the size of the index diagnostic for the investigated CT excitation.