In this letter, we investigate the pole structure of dynamical polarizabilities computed within the equation-of-motion coupled-cluster (EOM-CC) theory. We show, both theoretically and numerically, that approximate EOM-CC schemes such as, for example, the EOM-CC singles and doubles model exhibit an incorrect pole structure in which the poles that reflect the excitations from the target state (i.e., the EOM-CC state) are supplemented by artificial poles due to excitations from the CC reference state. These artificial poles can be avoided by skipping the amplitude response and reverting to a sum-over-states formulation. While numerical results are generally in favor of such a solution, its major drawback is that this scheme violates size extensivity.

中文翻译：

---

交流：运动方程耦合簇理论中动态极化率张量的极点结构

在这封信中，我们研究了在运动方程耦合簇（EOM-CC）理论中计算出的动态极化率的极点结构。我们从理论和数值上都表明，近似的EOM-CC方案，例如EOM-CC单双模型，表现出不正确的极点结构，其中的极点反映了来自目标状态的激发（即EOM -CC状态）由于来自CC参考状态的激励而由人造极补充。通过跳过幅度响应并恢复为求和状态公式，可以避免这些人造极点。尽管数值结果通常都支持这种解决方案，但其主要缺点是该方案违反了尺寸扩展性。