Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States.
J Chem Theory Comput. 2018 Nov 13;14(11):5597-5607. doi: 10.1021/acs.jctc.8b00171. Epub 2018 Oct 18.
A reduced-complexity variant of equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) method is formulated in terms of state-averaged excited-state pair natural orbitals (PNO) designed to describe manifolds of excited states. State-averaged excited-state PNOs for the target manifold are determined by averaging CIS(D) pair densities over the model manifold. The performance of the PNO-EOM-CCSD approach has been tested with the help of a distributed-memory parallel canonical EOM-CCSD implementation within the Massively Parallel Quantum Chemistry program that allows treatment of systems with 50+ atoms using realistic basis sets with 1000+ functions. The use of state-averaged PNOs offers several potential advantages relative to the recently proposed state-specific PNOs: our approach is robust with respect to root flipping and state degeneracies, it is more economical when computing large manifolds of states, and it simplifies evaluation of transition-specific observables such as dipole moments. With the PNO truncation threshold of 10, the errors in excitation energies are on average below 0.02 eV for the first six singlet states of 28 organic molecules included in the standard test set of Thiel and co-workers ( J. Chem. Phys. 2008, 128, 134110) with 50-70 state-averaged PNOs per pair.
本文提出了一种基于态平均激发态对自然轨道（PNO）的简化运动方程耦合簇单双激发（EOM-CCSD）方法，旨在描述激发态的流形。目标流形的态平均激发态 PNO 是通过在模型流形上平均 CIS(D) 对密度来确定的。借助 Massively Parallel Quantum Chemistry 程序中的分布式内存并行正则 EOM-CCSD 实现，对 PNO-EOM-CCSD 方法的性能进行了测试，该程序允许使用具有 1000 多个函数的真实基组处理具有 50 多个原子的系统。与最近提出的特定态 PNO 相比，态平均 PNO 具有几个潜在优势：我们的方法对根翻转和态简并具有鲁棒性，在计算大量态的流形时更经济，并且简化了对特定跃迁的可观测量（如偶极矩）的评估。使用 PNO 截断阈值为 10，对于 Thiel 等人（J. Chem. Phys. 2008, 128, 134110）标准测试集中包含的 28 个有机分子的前六个单重态的激发能误差平均低于 0.02 eV，每对具有 50-70 个态平均 PNO。
