Grotjahn Robin, Maier Toni M, Michl Josef, Kaupp Martin
Institut für Chemie, Theoretische Chemie/Quantenchemie, Sekr. C7, Technische Universität Berlin , Straße des 17. Juni 135, D-10623 Berlin, Germany.
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 16110 Prague 6, Czech Republic.
J Chem Theory Comput. 2017 Oct 10;13(10):4984-4996. doi: 10.1021/acs.jctc.7b00699. Epub 2017 Sep 25.
Chromophores suitable for singlet fission need to meet specific requirements regarding the relative energies of their S, S, and T (and T) electronic states. Accurate quantum-chemical computations of the corresponding energy differences are thus highly desirable for materials design. Methods based on density functional theory (DFT) have the advantage of being applicable to larger, often more relevant systems compared to more sophisticated post-Hartree-Fock methods. However, most exchange-correlation functionals do not provide the needed accuracy, in particular, due to an insufficient description of the T state. Here we use a recent singlet fission chromophore test set ( Wen , J. ; Havlas , Z. ; Michl , J. J. Am. Chem. Soc. 2015 , 137 , 165 - 172 ) to evaluate a wide range of DFT-based methods, with an emphasis on local hybrid functionals with a position-dependent exact-exchange admixture. New reference vertical CC2/CBS benchmark excitation energies for the test set have been generated, which exhibit somewhat more uniform accuracy than the previous CASPT2-based data. These CC2 reference data have been used to evaluate a wide range of functionals, comparing full linear-response TDDFT, the Tamm-Dancoff approximation (TDA), and ΔSCF calculations. Two simple two-parameter local hybrid functionals and the more empirical M06-2X global meta-GGA hybrid provide the overall best accuracy. Due to its lower empiricism and wide applicability, the Lh12ct-SsifPW92 local hybrid is suggested as the main ingredient of an efficient computational protocol for prediction of the relevant excitation energies in singlet fission chromophores. Full TDDFT for the S, S, and T excitations is combined with ΔSCF for the T excitations. Making use also of some error compensation with suitable DFT-optimized structures, even the most critical T excitations can be brought close to the target accuracy of 0.20 eV, while the other excitation energies are obtained even more accurately. This fully DFT-based protocol should become a useful tool in the field of singlet fission.
适用于单线态裂变的发色团需要在其S、S和T（以及T）电子态的相对能量方面满足特定要求。因此，对于材料设计而言，对相应能量差进行精确的量子化学计算是非常必要的。与更复杂的后哈特里-福克方法相比，基于密度泛函理论（DFT）的方法具有适用于更大、通常更相关体系的优势。然而，大多数交换相关泛函无法提供所需的精度，特别是由于对T态的描述不足。在此，我们使用最近的一个单线态裂变发色团测试集（Wen, J.; Havlas, Z.; Michl, J. J. Am. Chem. Soc. 2015, 137, 165 - 172）来评估一系列基于DFT的方法，重点是具有位置依赖精确交换混合的局域杂化泛函。已经生成了该测试集新的参考垂直CC2/CBS基准激发能，其精度比以前基于CASPT2的数据更为均匀。这些CC2参考数据已用于评估一系列泛函，比较了全线性响应TDDFT、塔姆-丹科夫近似（TDA）和ΔSCF计算。两种简单的双参数局域杂化泛函和经验性更强的M06-2X全局元广义梯度近似杂化泛函总体精度最佳。由于其较低的经验性和广泛的适用性，建议将Lh12ct-SsifPW92局域杂化泛函作为预测单线态裂变发色团相关激发能的高效计算方案的主要组成部分。对S、S和T激发采用全TDDFT，对T激发采用ΔSCF。同时利用一些合适的DFT优化结构进行误差补偿，即使是最关键的T激发也能接近0.20 eV的目标精度，而其他激发能的获得则更为精确。这种完全基于DFT的方案应成为单线态裂变领域的有用工具。
