Linear and quadratic internally contracted multireference coupled-cluster approximations
Linear and quadratic internally contracted multireference coupled-cluster approximations
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DOI：
10.1063/1.5095070
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发表时间：
2019-05-21
影响因子：
4.4
通讯作者：
Koehn, Andreas
中科院分区：
文献类型：
--
作者：
Black, Joshua A.;Koehn, Andreas
线性和二次近似的内部收缩多参考耦合簇（icMRCC）方法的实施和分析，通过使用链接和非链接耦合簇形式主义。这包括基于微扰理论以及耦合电子对近似CEPA（0）的方法。所有近似值之间的相似性和差异有助于突出和引发关于icMRCC分析方法学特性的讨论。在计算势能曲线（佩奇）时，观察到线性icMRCC能量的不连续性。使用图解表示，导致但也减少这些不连续性的术语被识别。对于基准测试用例，如计算佩奇，单重态-三重态分裂和势垒高度，多参考CEPA（0）近似表现良好;然而，它缺乏大小一致性，因此不能代表开发计算成本低且准确的icMRCC方法的目标。由AIP Publishing授权出版。
Linear and quadratic approximations to the internally contracted multireference coupled-cluster (icMRCC) method are implemented and analyzed by using the linked and unlinked coupled-cluster formalisms. This includes methods based on perturbation theory as well as the coupled-electron pair approximation, CEPA(0). The similarities and differences between all the approximations serve to highlight and provoke discussion about methodological peculiarities of the icMRCC ansatz. When calculating potential energy curves (PECs), discontinuities are observed for the linear icMRCC energies. Using a diagrammatic representation, the terms that cause but also reduce these discontinuities are identified. For benchmarking test cases such as calculating PECs, singlet-triplet splittings, and barrier heights, the multireference CEPA(0) approximation performs well; however, it suffers from a lack of size consistency and so cannot represent a step forward to the goal of developing a computationally cheap and accurate icMRCC method. Published under license by AIP Publishing.