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首页> 外文期刊>The Journal of Chemical Physics >Linear and quadratic internally contracted multireference coupled-cluster approximations
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Linear and quadratic internally contracted multireference coupled-cluster approximations

机译：线性和二次内部收缩的多推导耦合簇近似

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摘要

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.
机译：通过使用链接和未链接的耦合簇形式主义来实现和分析内部收缩多推导耦合集群（ICMRCC）方法的线性和二次近似。这包括基于扰动理论的方法以及耦合电子对近似，CEPA（0）。所有近似之间的相似性和差异有助于突出和挑起关于ICMRCC Ansatz的方法论特性的探讨。在计算潜在的能量曲线（PEC）时，观察到线性ICMRCC能量的不连续性。使用示意性表示，识别出原因但也减少这些不连续性的术语。对于基准测试案例，例如计算PECS，单向三联分裂和屏障高度，Multiference CEPA（0）近似表现良好;然而，它受到缺乏大小的一致性，因此不能代表到开发计算便宜和准确的ICMRCC方法的目标的前进。通过AIP发布在许可证下发布。

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