Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry , UiT The Arctic University of Norway , N-9037 Tromsø , Norway.
Department of Physical and Quantum Chemistry, Faculty of Chemistry , Wrocław University of Science and Technology , Wyb. Wyspiańskiego 27 , PL-50370 Wrocław , Poland.
J Chem Theory Comput. 2018 Jul 10;14(7):3677-3685. doi: 10.1021/acs.jctc.8b00245. Epub 2018 Jun 15.
The present work investigates the performance of exchange-correlation functionals in the prediction of two-photon absorption (2PA) strengths. For this purpose, we considered six common functionals used for studying 2PA processes and tested these on six organoboron chelates. The set consisted of two semilocal (PBE and BLYP), two hybrid (B3LYP and PBE0), and two range-separated (LC-BLYP and CAM-B3LYP) functionals. The RI-CC2 method was chosen as a reference level and was found to give results consistent with the experimental data that are available for three of the molecules considered. Of the six exchange-correlation functionals studied, only the range-separated functionals predict an ordering of the 2PA strengths that is consistent with experimental and RI-CC2 results. Even though the range-separated functionals predict correct relative trends, the absolute values for the 2PA strengths are underestimated by a factor of 2-6 for the molecules considered. An in-depth analysis, on the basis of the derived generalized few-state model expression for the 2PA strength for a coupled-cluster wave function, reveals that the problem with these functionals can be linked to underestimated excited-state dipole moments and, to a lesser extent, overestimated excitation energies. The semilocal and hybrid functionals exhibit less predictable errors and a variation in the 2PA strengths in disagreement with the reference results. The semilocal and hybrid functionals show smaller average errors than the range-separated functionals, but our analysis reveals that this is due to fortuitous error cancellation between excitation energies and the transition dipole moments. Our results constitute a warning against using currently available exchange-correlation functionals in the prediction of 2PA strengths and highlight the need for functionals that correctly describe the electron density of excited electronic states.
本工作研究了交换相关泛函在预测双光子吸收（2PA）强度方面的性能。为此，我们考虑了六种用于研究 2PA 过程的常用泛函，并在六种有机硼配合物上进行了测试。该集合由两个半局部（PBE 和 BLYP）、两个混合（B3LYP 和 PBE0）和两个范围分离（LC-BLYP 和 CAM-B3LYP）泛函组成。RI-CC2 方法被选为参考水平，发现它给出的结果与实验数据一致，实验数据可用于考虑的三种分子。在所研究的六种交换相关泛函中，只有范围分离泛函预测的 2PA 强度顺序与实验和 RI-CC2 结果一致。尽管范围分离泛函预测了相对趋势，但考虑的分子的 2PA 强度的绝对值被低估了 2-6 倍。基于对耦合簇波函数的 2PA 强度的推导广义少态模型表达式的深入分析，揭示了这些泛函的问题可以与低估的激发态偶极矩有关，在较小程度上与高估的激发能有关。半局部和混合泛函表现出更不可预测的误差，并且 2PA 强度的变化与参考结果不一致。半局部和混合泛函的平均误差小于范围分离泛函，但我们的分析表明，这是由于激发能和跃迁偶极矩之间的偶然误差抵消所致。我们的结果警告不要在预测 2PA 强度时使用当前可用的交换相关泛函，并强调需要正确描述激发电子态电子密度的泛函。
