Deustua J Emiliano, Shen Jun, Piecuch Piotr
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
J Chem Phys. 2021 Mar 28;154(12):124103. doi: 10.1063/5.0045468.
We recently proposed a novel approach to converging electronic energies equivalent to high-level coupled-cluster (CC) computations by combining the deterministic CC(P;Q) formalism with the stochastic configuration interaction (CI) and CC Quantum Monte Carlo (QMC) propagations. This article extends our initial study [J. E. Deustua, J. Shen, and P. Piecuch, Phys. Rev. Lett. 119, 223003 (2017)], which focused on recovering the energies obtained with the CC method with singles, doubles, and triples (CCSDT) using the information extracted from full CI QMC and CCSDT-MC, to the CIQMC approaches truncated at triples and quadruples. It also reports our first semi-stochastic CC(P;Q) calculations aimed at converging the energies that correspond to the CC method with singles, doubles, triples, and quadruples (CCSDTQ). The ability of the semi-stochastic CC(P;Q) formalism to recover the CCSDT and CCSDTQ energies, even when electronic quasi-degeneracies and triply and quadruply excited clusters become substantial, is illustrated by a few numerical examples, including the F-F bond breaking in F, the automerization of cyclobutadiene, and the double dissociation of the water molecule.
我们最近提出了一种新方法，通过将确定性耦合簇（CC）形式主义与随机组态相互作用（CI）以及CC量子蒙特卡罗（QMC）传播相结合，来收敛与高级耦合簇（CC）计算等效的电子能量。本文扩展了我们的初步研究[J. E. 德斯塔、J. 沈和P. 皮丘克，《物理评论快报》119, 223003 (2017)]，该研究侧重于利用从全CI QMC和CCSDT - MC中提取的信息来恢复用单双三激发耦合簇（CCSDT）方法获得的能量，此次扩展到了截断在三激发和四激发的CIQMC方法。本文还报告了我们首次旨在收敛与单双三四激发耦合簇（CCSDTQ）方法对应的能量的半随机CC(P;Q)计算。通过几个数值例子说明了半随机CC(P;Q)形式主义即使在电子准简并以及三重和四重激发簇变得显著时恢复CCSDT和CCSDTQ能量的能力，这些例子包括F中F - F键的断裂、环丁二烯的自动异构化以及水分子的双解离。
