Anion resonances are formed as metastable intermediates in low-energy electron-induced reactions. Due to the finite lifetimes of resonances, applying standard Hermitian formalism for their characterization presents a vexing problem for computational chemists. Numerous modifications to conventional quantum chemical methods have enabled satisfactory characterization of resonances, but specific issues remain, especially in describing two-particle one-hole (2p–1h) resonances. An accurate description of these resonances and their coupling with single-particle resonances requires a multireference approach. We propose a projected complex absorbing potential (CAP) implementation within the multireference configuration interaction (MRCI) framework to characterize single-particle and 2p–1h resonances. As a first application, we use the projected-CAP-MRCI approach to characterize and benchmark the ²Π_g shape resonance in N₂^–. We test its performance as a function of the size of the subspace and other parameters, and we compute the complex potential energy surface of the ²Π_g shape resonance to show that a smooth curve is obtained. One key benefit of MRCI is that it can describe Feshbach resonances (most common examples of 2p–1h resonances) at the same footing as shape resonances. Therefore, it is uniquely positioned to describe mixing between the different channels. To test these additional capabilities, we compute Feshbach resonances in H₂O^– and anions of dicyanoethylene isomers. We find that CAP-MRCI can efficiently capture the mixing between the Feshbach and shape resonances in dicyanoethylene isomers, which has significant consequences for their lifetimes.

中文翻译：

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形状和 Feshbach 共振的投影复杂吸收势多参考配置交互方法

阴离子共振在低能电子诱导反应中形成为亚稳态中间体。由于共振的寿命有限，应用标准的 Hermitian 形式来表征它们对计算化学家来说是一个令人头疼的问题。对传统量子化学方法的许多修改已经能够令人满意地表征共振，但仍然存在特定问题，特别是在描述双粒子单孔（2p-1h）共振时。准确描述这些共振及其与单粒子共振的耦合需要多参考方法。我们在多参考配置相互作用 (MRCI) 框架内提出了一个预计的复合吸收势 (CAP) 实施方案，以表征单粒子和 2p-1h 共振。作为第一个应用程序，_{N 2} ^–中的2 Π _g形共振。^{我们测试了它作为子空间大小和其他参数的函数的性能，我们计算了2} Π _g形状共振的复势能面，以表明获得了平滑曲线。MRCI 的一个主要优点是它可以在与形状共振相同的基础上描述 Feshbach 共振（最常见的 2p-1h 共振示例）。因此，它具有独特的定位来描述不同通道之间的混合。_{为了测试这些额外的能力，我们计算了 H 2} O中的 Feshbach 共振^——和二氰基乙烯异构体的阴离子。我们发现 CAP-MRCI 可以有效地捕捉 Feshbach 和二氰基乙烯异构体中的形状共振之间的混合，这对它们的寿命产生重大影响。