Wang Zhifan, Hu Shu, Wang Fan, Guo Jingwei
College of Chemistry, Sichuan University, Chengdu 610064, People's Republic of China.
Key Laboratory of Chemical Laser, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China.
J Chem Phys. 2015 Apr 14;142(14):144109. doi: 10.1063/1.4917041.
In this work, we report implementation of the equation-of-motion coupled-cluster method for doubly ionized states (EOM-DIP-CC) with spin-orbit coupling (SOC) using a closed-shell reference. Double ionization potentials (DIPs) are calculated in the space spanned by 2h and 3h1p determinants with the EOM-DIP-CC approach at the CC singles and doubles level (CCSD). Time-reversal symmetry together with spatial symmetry is exploited to reduce computational effort. To circumvent the problem of unstable dianion references when diffuse basis functions are included, nuclear charges are scaled. Effect of this stabilization potential on DIPs is estimated based on results from calculations using a small basis set without diffuse basis functions. DIPs and excitation energies of some low-lying states for a series of open-shell atoms and molecules containing heavy elements with two unpaired electrons have been calculated with the EOM-DIP-CCSD approach. Results show that this approach is able to afford a reliable description on SOC splitting. Furthermore, the EOM-DIP-CCSD approach is shown to provide reasonable excitation energies for systems with a dianion reference when diffuse basis functions are not employed.
在本工作中，我们报告了使用闭壳层参考态，通过含自旋轨道耦合（SOC）的运动方程耦合簇方法（EOM-DIP-CC）来处理双电离态。采用EOM-DIP-CC方法在耦合簇单双激发（CCSD）水平下，在由2h和3h1p行列式所张成的空间中计算双电离势（DIP）。利用时间反演对称性和空间对称性来减少计算量。为了规避包含弥散基函数时双负离子参考态不稳定的问题，对核电荷进行了缩放。基于使用不含弥散基函数的小基组计算结果，估算了这种稳定化势对DIP的影响。采用EOM-DIP-CCSD方法计算了一系列含有两个未成对电子的重元素开壳层原子和分子的一些低激发态的DIP和激发能。结果表明，该方法能够对SOC分裂给出可靠的描述。此外，当不使用弥散基函数时，EOM-DIP-CCSD方法对于具有双负离子参考态的体系能给出合理的激发能。
