标题： 无自旋广义常规序耦合簇 显示英文标题

标题： Spin-free Generalised Normal Ordered Coupled Cluster

摘要： 我们提出了一种无自旋、规模广义且规模一致的耦合簇方法，该方法基于广义正常有序指数假设。 该方法是对任意自旋本征函数的单参考耦合簇理论的自然推广。 通过广义正常序形式主义，工作方程具有规模广义性，并通过自旋集合方法实现无自旋。 通过仅选择那些将参考函数投影到一阶相互作用空间的激发态，消除了激发态之间的冗余。 此外，通过利用局域轨道，所提出的方法可以规模一致地描述解离为开壳层碎片。 在单和双激发理论水平上对典型多参考系统进行的数值结果与现有的多参考方法相当，但工作方程更为简洁。 显示英文摘要

摘要： We present a spin-free, size-extensive, and size-consistent coupled cluster method based on a generalised normal ordered exponential ansatz. This approach is a natural generalisation of single-reference coupled cluster theory for arbitrary spin eigenfunctions. The working equations are size-extensive through the generalised normal order formalism, and made spin-free with the spin-ensemble approach. Redundancies amongst excitations are eliminated by selecting only those excitations that project the reference function onto the first-order interacting space. Furthermore, by utilising localised orbitals, the proposed method describes dissociation into open-shell fragments size-consistently. Numerical results on prototypical multireference systems at the singles and doubles level of theory are competitive with existing multireference approaches, yet with more compact working equations.