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Stochastic multi-reference perturbation theory with application to the linearized coupled cluster method

机译：随机多参考扰动理论，应用于线性化耦合簇法

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摘要

In this article we report a stochastic evaluation of the recently proposed multireference linearized coupled cluster theory [S. Sharma and A. Alavi, J. Chem. Phys. 143, 102815 (2015)]. In this method, both the zeroth-order and first-order wavefunctions are sampled stochastically by propagating simultaneously two populations of signed walkers. The sampling of the zeroth-order wavefunction follows a set of stochastic processes identical to the one used in the full configuration interaction quantum Monte Carlo (FCIQMC) method. To sample the first-order wavefunction, the usual FCIQMC algorithm is augmented with a source term that spawns walkers in the sampled first-order wavefunction from the zeroth-order wavefunction. The second-order energy is also computed stochastically but requires no additional overhead outside of the added cost of sampling the first-order wavefunction. This fully stochastic method opens up the possibility of simultaneously treating large active spaces to account for static correlation and recovering the dynamical correlation using perturbation theory. The method is used to study a few benchmark systems including the carbon dimer and aromatic molecules. We have computed the singlet-triplet gaps of benzene and m-xylylene. For m-xylylene, which has proved difficult for standard complete active space self consistent field theory with perturbative correction, we find the singlet-triplet gap to be in good agreement with the experimental values. Published by AIP Publishing.
机译：在本文中，我们报道了最近提出的多引用的随机评价线性耦合簇理论[S. Sharma和A.阿拉维，J.化学。物理。 143，102815（2015）]。在该方法中，无论是零阶和一阶的波函数通过同时传播签署步行者的两个群体随机采样。零级波函数的采样遵循一组等同于完整的配置相互作用量子蒙特卡洛（FCIQMC）方法中使用的一个随机过程。到采样第一阶的波函数，通常的FCIQMC算法增加了一个源项是，在从零阶的波函数的采样的第一阶的波函数产卵步行者。二阶能量也随机地计算，但需要采样第一阶波函数的增加的成本的没有额外的开销之外。这充分随机方法开辟了同时处理大量活跃的空间，以帐户为静态关联和使用微扰理论恢复动态相关的可能性。该方法用于研究几个基准系统，包括碳二聚物和芳族分子。我们已计算出苯和间 - 亚二甲苯基的单重态 - 三重态的间隙。对于间苯二甲胺，这已被证明难以完成标准活化空间自洽场理论与微扰修正，我们发现单，三重态能隙是与实验值基本一致。通过AIP发布发布。

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