Lu Yanzhao, Wang Zhifan, Wang Fan
Institute of Atomic and Molecular Physics, Key Laboratory of High Energy Density Physics and Technology, Ministry of Education, Sichuan University, Chengdu 610065, People's Republic of China.
College of Chemistry and Life Science, Chengdu Normal University, Chengdu 611130, People's Republic of China.
J Chem Phys. 2022 Mar 21;156(11):114111. doi: 10.1063/5.0076462.
The intermediate Hamiltonian Fock-space coupled-cluster methods at the singles and doubles level (IHFSCCSD) for excitation energies in the (1p, 1h) sector, double ionization potentials in the (0p, 2h) sector, and double electron attachments in the (2p, 0h) sector of the Fock space are implemented based on the CCSD method with spin-orbit coupling (SOC) included in the post-Hartree-Fock treatment using a closed-shell reference in this work. The active space is chosen to contain those orbitals that have the largest contribution to principal ionized or electron-attached states obtained from the equation-of-motion coupled-cluster calculations. Both time-reversal symmetry and spatial symmetry are exploited in the implementation. Our results show that the accuracy of IHFSCCSD results is closely related to the active space, and the sufficiency of the active space can be assessed from the percentage of transitions within the active space. In addition, unreasonable results may be encountered when the ionized or electron-attached states with a somewhat larger contribution from double excitations are included to determine the active space and cluster operators in the (0p, 1h) or (1p, 0h) sector of the Fock space. A larger active space may be required to describe SO splitting reliably than that in the scalar-relativistic calculations in some cases. The IHFSCCSD method with SOC developed in this work can provide reliable results for heavy-element systems when a sufficient active space built upon the principal ionization potential/electron affinity states is adopted.
本文基于包含自旋轨道耦合（SOC）的耦合簇单双激发（CCSD）方法，采用闭壳层参考态，在哈特里 - 福克后处理中实现了用于福克空间（1p, 1h）扇区激发能、（0p, 2h）扇区双电离势以及（2p, 0h）扇区双电子附着的中级哈密顿量福克空间耦合簇单双激发（IHFSCCSD）方法。活性空间被选为包含那些对从运动方程耦合簇计算得到的主要电离或电子附着态贡献最大的轨道。在实现过程中利用了时间反演对称性和空间对称性。我们的结果表明，IHFSCCSD结果的准确性与活性空间密切相关，并且活性空间的充分性可以从活性空间内跃迁的百分比来评估。此外，当在确定福克空间（0p, 1h）或（1p, 0h）扇区的活性空间和簇算符时包含来自双激发贡献稍大的电离或电子附着态时，可能会遇到不合理的结果。在某些情况下，可能需要比标量相对论计算中更大的活性空间来可靠地描述SO分裂。当采用基于主要电离势/电子亲和能态构建的足够活性空间时，本文开发的具有SOC的IHFSCCSD方法可以为重元素系统提供可靠的结果。
