We investigate performance of the equation-of-motion coupled-cluster method at the single and doubles level (EOM-CCSD) and a series of approximate methods based on EOM-CCSD on electron affinities (EA) of closed-shell cations and neutral molecules with positive and negative EAs in this work. Our results confirm that P-EOM-MBPT2 can provide reasonable EAs when molecules with significant multireference character are not considered and its mean absolute error on EAs of these molecules is around or less than 0.2 eV. Its accuracy is comparable to that of the more expensive EOM-CCSD(2) method. Results of EOM-CCSD(2), P-EOM-MBPT2, and CIS(D_∞) indicate that the [[H, a_c⁺], T₂] term in the 1h2p–1h block is more important on EAs than the term neglected in the 1h2p–1h2p block in P-EOM-MBPT2. We proposed an economical method where EAs from CIS(D_∞) are corrected by treating this [[H, a_c⁺], T₂] term in the 1h2p–1h block perturbatively [corr-CIS(D_∞)]. EAs with corr-CIS(D_∞) agree very well with those of P-EOM-MBPT2 with a difference of less than 0.02 eV. Computational scaling of this method is N⁴ for the iterative part and N⁵ for some non-iterative steps. Its storage requirement is only of OV³. Corr-CIS(D_∞) is an economical and reliable method on EAs, and it can be applied to EAs of large molecules.

中文翻译：

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封闭壳分子电子亲和力的近似运动方程耦合簇方法

我们研究了运动方程耦合簇方法在单双峰水平下（EOM-CCSD）的性能以及一系列基于EOM-CCSD的闭壳阳离子和中性分子电子亲和力（EA）的近似方法在这项工作中具有正面和负面的EA。我们的结果证实，当不考虑具有显着多参考特征的分子且其在这些分子的EA上的平均绝对误差约为或小于0.2 eV时，P-EOM-MBPT2可以提供合理的EA。其准确性可与更昂贵的EOM-CCSD（2）方法媲美。EOM-CCSD（2）的结果，P-EOM-MBPT2，和CIS（d _∞）表明，[[ ħ，一个_Ç ⁺ ]，Ť ₂在EA上，1h2p-1h块中的]术语比P-EOM-MBPT2中1h2p-1h2p块中所忽略的术语更重要。我们提出了一种经济的方法，其中来自CIS（d查点_∞）通过处理该[[校正ħ，一个_Ç ⁺ ]，Ť ₂在1h2p-1H块]术语微扰[更正件-CIS（d _∞）]。用科尔-CIS（d查点_∞）吻合得很好与P-EOM-MBPT2的具有小于0.02电子伏特的差值。该方法的计算缩放比例对于迭代部分为N ⁴，对于某些非迭代步骤为N ⁵。其存储要求仅为OV ³。Corr-CIS（_D∞）是一种经济，可靠的EA方法，可应用于大分子EA。