We derive the crossing conditions at conical intersections between electronic states in coupled cluster theory and show that if the coupled cluster Jacobian matrix is nondefective, two (three) independent conditions are correctly placed on the nuclear degrees of freedom for an inherently real (complex) Hamiltonian. Calculations using coupled cluster theory on a 2¹A′/3¹A′ conical intersection in hypofluorous acid illustrate the nonphysical artifacts associated with defects at accidental same-symmetry intersections. In particular, the observed intersection seam is folded about a space of the correct dimensionality, indicating that minor modifications to the theory are required for it to provide a correct description of conical intersections in general. We find that an accidental symmetry allowed 1¹A″/2¹A″ intersection in hydrogen sulfide is properly described, showing no artifacts as well as linearity of the energy gap to first order in the branching plane.

中文翻译：

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耦合聚类理论中的交叉条件

我们用耦合簇理论推导了电子态之间圆锥形相交处的交叉条件，并表明，如果耦合簇雅可比矩阵是无缺陷的，则固有固有（复杂）哈密顿量的两个（三个）独立条件正确地置于核自由度上。使用耦合簇理论在2 ¹ A '/ 3 ¹ A上进行计算次氟酸中的圆锥形交叉点说明了与偶然的相同对称交叉点处的缺陷相关的非物理伪影。特别地，所观察到的相交接缝围绕正确尺寸的空间折叠，这表明需要对该理论进行较小的修改，以在总体上提供对圆锥形相交的正确描述。我们发现正确描述了硫化氢中1 ¹ A ″ / 2 ¹ A ″相交的偶然对称性，在分支平面中未显示任何伪像以及能隙与一阶的线性关系。