激子耦合团簇理论
Excitonic Coupled-cluster Theory
摘要：
耦合集群理论的一个变体在这里描述，其中的自由度是内部关联状态之间的片段的波动。片段间相互作用上的片段内相关性的影响是预先计算的，并永久折叠成一个有效的哈密顿量，从而避免了与耦合波动相关的局部弛豫的冗余评估。一篇配套文章表明，一个低标度的步骤可以用来铸造成所需的形式的电子哈密顿量的真实系统。这里给出了两个非共价相互作用的原理证明。一种是使用谐振子，其精度和算法结构可以在比较中仔细控制。另一个使用小的电子系统（Be原子），以证明令人信服的准确性和效率，也当碎片间的电子交换和电荷转移必须处理。由于全局计算的成本并不直接取决于用于碎片的相关模型，这应该提供了一种将困难的电子结构问题纳入大型系统的方法。该框架为构建可调的、系统可改进的方法来捕获与大量其他系统交互的系统属性开辟了一条有前途的道路。扩展到激发态也是简单的。
英文摘要：
A variant of coupled-cluster theory is described here, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction are pre-computed and permanently folded into an effective Hamiltonian, thus avoiding redundant evaluations of local relaxations associated with coupled fluctuations. A companion article shows that a low-scaling step may be used to cast the electronic Hamiltonians of real systems into the form required. Two proof-of-principle demonstrations are presented here for non-covalent interactions. One uses harmonic oscillators, for which accuracy and algorithm structure can be carefully controlled in comparisons. The other uses small electronic systems (Be atoms) to demonstrate compelling accuracy and efficiency, also when inter-fragment electron exchange and charge transfer must be handled. Since the cost of the global calculation does not depend directly on the correlation models used for the fragments, this should provide a way to incorporate difficult electronic structure problems into large systems. This framework opens a promising path for building tunable, systematically improvable methods to capture properties of systems interacting with a large number of other systems. The extension to excited states is also straightforward.
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