Restricted active space configuration interaction methods for strong correlation: Recent developments,Wiley Interdisciplinary Reviews: Computational Molecular Science

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Restricted active space configuration interaction methods for strong correlation: Recent developments
Wiley Interdisciplinary Reviews: Computational Molecular Science ( IF 16.8 ) Pub Date : 2021-07-12 , DOI: 10.1002/wcms.1561
David Casanova _{1,

2}

Affiliation

In this review we outline the theory and recent progress of the restricted active space configuration interaction (RASCI) methodology within the hole and particle approximation. The RASCI is a single reference approach based on the splitting of the orbital space in different subsets, in which the target CI space is expressed by the concomitant number of electrons and empty orbitals in each subspace. Initially, the method was born as a spin complete version of the spin-flip ansatz able to deal with any number of unpaired electrons. Since then, the method has experienced several improvements related to its theoretical foundations, its efficient implementation, in the characterization of RASCI wave functions, and in the calculation of molecular properties. It has shown to be especially suitable for the characterization of medium to large molecular diradicals and polyradicals, and to the study of photophysical processes involving open-shell species and/or multiexcitonic states, like in the singlet fission reaction. But, despite this success, several limitations emerge from the sever truncation of the excitation operator, which might translate into inaccurate relative energies between different regions of the potential energy surface, and overestimated (or underestimated) excitation energies. These errors are associated with the lack of dynamic correlation, which has motivated the development and implementation of various improvements based on multi-reference perturbation theory and to blend the RASCI wave function with density functional theory through range separation of electron–electron interactions. Finally, we discuss some of the properties available from RASCI wave functions and give potential future developments.

中文翻译：

强相关的受限主动空间配置交互方法：最新进展

在这篇综述中，我们概述了孔和粒子近似中受限主动空间配置相互作用（RASCI）方法的理论和最新进展。RASCI 是一种基于轨道空间在不同子集中分裂的单一参考方法，其中目标 CI 空间由每个子空间中伴随的电子数和空轨道数表示。最初，该方法作为自旋翻转 ansatz 的自旋完整版本诞生，能够处理任意数量的未配对电子。从那时起，该方法在其理论基础、有效实施、RASCI 波函数表征和分子性质计算方面经历了几次改进。它已被证明特别适用于表征中到大分子双自由基和多自由基，以及研究涉及开壳物质和/或多激子态的光物理过程，如单线态裂变反应。但是，尽管取得了成功，但激发算子的截断仍然存在一些限制，这可能会转化为势能表面不同区域之间的不准确相对能量，以及高估（或低估）的激发能量。这些错误与缺乏动态相关性有关，这推动了基于多参考微扰理论的各种改进的开发和实施，并通过电子 - 电子相互作用的范围分离将 RASCI 波函数与密度泛函理论相结合。最后，我们讨论了 RASCI 波函数的一些可用特性，并给出了潜在的未来发展。

更新日期：2021-07-12

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