Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
Department of Chemistry and the PULSE Institute, Stanford University, Stanford, California 94305, USA.
J Chem Phys. 2017 Oct 28;147(16):164105. doi: 10.1063/1.4998724.
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 2A'/3A' 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 1A″/2A″ 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.
我们推导出了耦合簇理论中电子态之间的交叉条件，并表明如果耦合簇雅可比矩阵是非退化的，则对于固有实（复）哈密顿量，在核自由度上正确放置了两个（三个）独立条件。在氢氟酸的 2A'/3A' 交叉点处使用耦合簇理论进行的计算说明了与意外同对称交叉点处缺陷相关的非物理伪影。具体来说，观察到的交叉缝围绕正确维度的空间折叠，这表明需要对理论进行微小修改，以使其能够一般正确描述交叉点。我们发现，在硫化氢中，一个意外的对称性允许的 1A″/2A″ 交叉点得到了很好的描述，没有伪影，并且在分支平面上能量隙的线性度也是一阶的。
