研究Thiel基准集上的激发态特异性微扰理论
Studying excited-state-specific perturbation theory on the Thiel set
AI总结：
本研究评估了激发态特异性二阶微扰理论（ESMP2）在Thiel基准集上的表现，发现正则化可提升其精度，并利用双激发范数低成本检测双激发特征。
摘要：
我们探索了一种最近引入的$N^5$标度激发态特异性二阶微扰理论（ESMP2）在Thiel基准集的单重态激发上的性能。我们发现，在没有正则化的情况下，ESMP2对$\pi$体系大小相当敏感，在小$\pi$体系的分子中表现良好，但在具有较大$\pi$体系的分子中表现不佳。通过正则化，ESMP2对$\pi$体系大小的敏感性大大降低，并且在Thiel集上显示出比CC2、EOM-CCSD、CC3以及多种含时密度泛函方法更高的整体精度。不出所料，即使经过正则化的ESMP2在此测试集上的精度也不如多参考微扰理论，这在一定程度上可以解释为该集合包含了一些双激发态，但没有任何强电荷转移态，而后者通常对态平均方法构成挑战。除了能量学之外，我们发现ESMP2的双激发范数提供了一种相对低成本的方式来测试双激发特征，而无需定义活性空间。
英文摘要：
We explore the performance of a recently-introduced $N^5$-scaling excited-state-specific second order perturbation theory (ESMP2) on the singlet excitations of the Thiel benchmarking set. We find that, without regularization, ESMP2 is quite sensitive to $π$ system size, performing well in molecules with small $π$ systems but poorly in those with larger $π$ systems. With regularization, ESMP2 is far less sensitive to $π$ system size and shows a higher overall accuracy on the Thiel set than CC2, EOM-CCSD, CC3, and a wide variety of time-dependent density functional approaches. Unsurprisingly, even regularized ESMP2 is less accurate than multi-reference perturbation theory on this test set, which can in part be explained by the set's inclusion of some doubly excited states but none of the strong charge transfer states that often pose challenges for state-averaging. Beyond energetics, we find that the ESMP2 doubles norm offers a relatively low-cost way to test for doubly excited character without the need to define an active space.
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