Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo
Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo
复制标题
有机双自由基和多并苯的单重态-三重态能隙与辅助场量子蒙特卡罗
DOI：
10.1021/acs.jctc.9b00534
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发表时间：
2019
影响因子：
5.5
通讯作者：
Friesner, Richard A.
中科院分区：
文献类型：
--
作者：
Shee, James;Arthur, Evan J.;Zhang, Shiwei;Reichman, David R.;Friesner, Richard A.
最低单线态和三重态之间的能隙是化学光催化中的一个重要量，其相关应用范围从光学上转换中的三重态融合到有机发光器件的设计。单重态-三重态（ST）间隙的实验室初始预测是具有挑战性的，因为所涉及的状态可能具有双基性质，再加上相关分子的潜在大尺寸。在这项工作中，我们证明了无相辅助场量子蒙特卡罗（ph-AFQMC）可以准确预测具有高度双基性质的单重态化学系统的ST间隙，包括一组13个小分子和苯的理论、间位和对异构体。对于气相实验，使用CASSCF试验波函数的ph-AFQMC平均误差为~ 1 kcal/mol。此外，我们发现在自旋投影技术的背景下，使用不受限制的单行列式试波函数的ph-AFQMC可以产生同样高的精度，即使对于非常大的系统也可以很容易地获得。我们继续表明，这种可扩展的方法能够产生准确的ST间隙为所有线性多聚烯的实验测量存在，即萘，蒽，四烯和并五烯。我们的结果提出了一种基于自旋污染程度为单决定试验波函数选择不受限制的Hartree-Fock或Kohn-Sham轨道的方案。这些发现为未来研究涉及具有实质性二元特征的大分子的特定光化学过程铺平了道路。
The energy gap between the lowest-lying singlet and triplet states is an important quantity in chemical photocatalysis, with relevant applications ranging from triplet fusion in optical upconversion to the design of organic light-emitting devices. Theab initioprediction of singlet–triplet (ST) gaps is challenging due to the potentially biradical nature of the involved states, combined with the potentially large size of relevant molecules. In this work, we show that phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) can accurately predict ST gaps for chemical systems with singlet states of highly biradical nature, including a set of 13 small molecules and theortho-,meta-, andpara- isomers of benzyne. With respect to gas-phase experiments, ph-AFQMC using CASSCF trial wave functions achieves a mean averaged error of ∼1 kcal/mol. Furthermore, we find that in the context of a spin-projection technique, ph-AFQMC using unrestricted single-determinant trial wave functions, which can be readily obtained for even very large systems, produces equivalently high accuracy. We proceed to show that this scalable methodology is capable of yielding accurate ST gaps for all linear polyacenes for which experimental measurements exist, that is, naphthalene, anthracene, tetracene, and pentacene. Our results suggest a protocol for selecting either unrestricted Hartree–Fock or Kohn–Sham orbitals for the single-determinant trial wave function, based on the extent of spin-contamination. These findings pave the way for future investigations of specific photochemical processes involving large molecules with substantial biradical character.