Folkestad Sarai Dery, Kruken Kristine Lauvstad, Koch Henrik
Department of Chemistry, Norwegian University of Science and Technology, NTNU, Trondheim 7491, Norway.
J Phys Chem A. 2025 Jul 31;129(30):6911-6917. doi: 10.1021/acs.jpca.5c01190. Epub 2025 Jul 21.
We present a spin-adapted coupled cluster singles and doubles model for the excitation energies of molecular doublets. The entanglement coupled cluster approach represents an unconventional take on the notorious problem of spin adaptation for open-shell species. In this approach, the high-spin open-shell molecular system is coupled to non-interacting bath orbitals to form a total closed-shell system. In entanglement coupled cluster theory, many of the attractive features of the spin-adapted closed-shell coupled cluster are retained: an unambiguous definition of the cluster operator and a terminating Baker-Campbell-Hausdorff expansion. The model produces excitation energies of a quality comparable to that of the closed-shell counterpart. Additionally, some ionized states that cannot be modeled accurately with the alternative equation-of-motion approach for ionized states can be described with the entanglement coupled cluster singles and doubles model.
我们提出了一种用于分子双重态激发能的自旋适配耦合簇单双激发模型。纠缠耦合簇方法是对开壳层物种自旋适配这一著名难题的一种非常规处理方式。在这种方法中，高自旋开壳层分子系统与非相互作用的浴轨道耦合，形成一个总闭壳层系统。在纠缠耦合簇理论中，保留了自旋适配闭壳层耦合簇的许多吸引人的特征：簇算符的明确定义以及终止的Baker-Campbell-Hausdorff展开。该模型产生的激发能质量与闭壳层对应模型相当。此外，一些用离子态的替代运动方程方法无法精确建模的离子态，可以用纠缠耦合簇单双激发模型来描述。
