Hirao Kimihiko, Chan Bun, Song Jong-Won, Bae Han-Seok
RIKEN Center for Computational Science, 7-1-26, Minatojima-minami-machi, Chuo-ku, Kobe 650-0047, Japan.
Fukui Institute for Fundamental Chemistry, Kyoto University, Takano, Nishihiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103, Japan.
J Phys Chem A. 2020 Oct 1;124(39):8079-8087. doi: 10.1021/acs.jpca.0c05414. Epub 2020 Sep 22.
Previously proposed theoretical schemes for estimating one-electron excitation energies using Kohn-Sham (KS) solutions with long-range corrected (LC) functionals are applied to the charge-transfer (CT) excitations of the ethylene···tetrafluoroethylene (CH-CF) system, and the CT complex between an aromatic donor (Ar = benzene, toluene, -xylene, naphthalene, anthracene, and various meso-substituted anthracenes) and the tetracyanoethylene (TCNE) acceptor. The CT excited state is described well as a single-electron excitation between specific orbitals of donor and acceptor. Thus, CT excitation energies are well approximated by the orbital energies because of the satisfaction of the Koopmans-type theorem and the asymptotic behavior of the LC functional. We have examined three computational schemes: scheme 1 employs the orbital energies for the neutral and cationic systems, scheme 2 utilizes orbital energies of just the cation, and in scheme 3, because the electron affinity of a molecule is the ionization energy of its anion, a scale factor is applied to enforce this identity. The present schemes reproduce the correct asymptotic behavior of CT excitation energy of CH···CF for the long intermolecular distances and give good agreement with accurate results. Calculated CT excitation energies for Ar-TCNE are compared with those of TD-DFT and ΔSCF methods. Scheme 1 with the optimal range-separation parameter μ accurately reproduces CT excitation energies for all Ar-TCNE systems and gives good agreement with the best TD-DFT calculations and experiment. Scheme 1, scheme 3, and TD-DFT show similar tendencies with respect to the variation in μ. Scheme 2 and ΔSCF approaches are rather insensitive to changes in μ, but both considerably underestimate the CT excitation energies for these systems. KS orbital energies are physically meaningful and they are practically useful; if the range-separation parameter is tuned, then good results can be obtained.
先前提出的使用具有长程校正（LC）泛函的Kohn-Sham（KS）解来估计单电子激发能的理论方案，被应用于乙烯···四氟乙烯（CH-CF）体系的电荷转移（CT）激发，以及芳香供体（Ar = 苯、甲苯、二甲苯、萘、蒽和各种中位取代蒽）与四氰基乙烯（TCNE）受体之间的CT复合物。CT激发态可以很好地描述为供体和受体特定轨道之间的单电子激发。因此，由于满足库普曼斯型定理和LC泛函的渐近行为，CT激发能可以很好地由轨道能量近似。我们研究了三种计算方案：方案1使用中性和阳离子体系的轨道能量，方案2仅利用阳离子的轨道能量，而在方案3中，由于分子的电子亲和能是其阴离子的电离能，应用一个比例因子来强制实现这种一致性。当前方案再现了CH···CF在长分子间距离时CT激发能的正确渐近行为，并与精确结果取得了良好的一致性。将计算得到的Ar-TCNE的CT激发能与TD-DFT和ΔSCF方法的结果进行了比较。具有最佳范围分离参数μ的方案1准确地再现了所有Ar-TCNE体系的CT激发能，并与最佳的TD-DFT计算结果和实验结果取得了良好的一致性。方案1、方案3和TD-DFT在μ的变化方面表现出相似的趋势。方案2和ΔSCF方法对μ的变化相当不敏感，但两者都显著低估了这些体系的CT激发能。KS轨道能量具有物理意义且实际有用；如果调整范围分离参数，就能得到良好的结果。
