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A truncation hierarchy of coupled cluster models of strongly correlated systems based on perfect-pairing references: The singles+doubles models

机译:基于完美配对参考的强相关系统的耦合簇模型的截断层次结构:单/双模型

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摘要

Paired, active-space treatments of static correlation are augmented with additional amplitudes to produce a hierarchy of parsimonious and efficient cluster truncations that approximate the total energy. The number of parameters introduced in these models grow with system size in a tractable way: two powers larger than the static correlation model it is built upon: for instance cubic for the models built on perfect pairing, fourth order for a perfect quadruples (PQ) reference, and fifth order for the models built on perfect hextuples. These methods are called singles+doubles (SD) corrections to perfect pairing, PQ, perfect hextuples, and two variants are explored. An implementation of the SD methods is compared to benchmark results for F2 and H2 O dissociation problems, the H4 and H8 model systems, and the insertion of beryllium into hydrogen. In the cases examined even the quartic number of parameters associated with PQSD is able to provide results which meaningfully improve on coupled-cluster singles doubles (CCSD) (which also has quartic amplitudes) and compete with existing multi-reference alternatives.
机译:静态相关的成对活动空间处理增加了额外的幅度,以生成近似总能量的简约高效簇截断层次。这些模型中引入的参数数量随系统规模的增长而增加:比其所基于的静态相关模型大2倍:例如,基于完美配对的模型为三次方,代表理想四倍体(PQ)的四阶参考,以及基于完美六面体的模型的五阶。这些方法被称为“单双加”(SD)校正,以实现完美配对,PQ,完美hextuple,并探讨了两种变体。将SD方法的实现与F2和H2 O解离问题,H4和H8模型系统以及将铍插入氢的基准结果进行比较。在所检查的情况下,甚至与PQSD相关的参数的四次数也能够提供有意义的结果,从而对耦合集群单打双打(CCSD)(也具有四次振幅)产生有意义的改善,并与现有的多参考替代项竞争。

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