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首页> 外文期刊>The Journal of Chemical Physics >Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster
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Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster

机译：多参考状态特定耦合簇中激励幅度的替代定义

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摘要

A central difficulty of state-specific Multi-Reference Coupled Cluster (MR-CC) in the multiexponential Jeziorski-Monkhorst formalism concerns the definition of the amplitudes of the single and double excitation operators appearing in the exponential wave operators. If the reference space is a complete active space (CAS), the number of these amplitudes is larger than the number of singly and doubly excited determinants on which one may project the eigenequation, and one must impose additional conditions. The present work first defines a state-specific reference-independent operator (T) over tilde (m) which acting on the CAS component of the wave function vertical bar Psi(m)(0)> maximizes the overlap between (1 + (T) over tilde (m))vertical bar Psi(m)(0)> and the eigenvector of the CAS-SD (Singles and Doubles) Configuration Interaction (CI) matrix vertical bar Psi(m)(CAS-SD)> i. This operator may be used to generate approximate coefficients of the triples and quadruples, and a dressing of the CAS-SD CI matrix, according to the intermediate Hamiltonian formalism. The process may be iterated to convergence. As a refinement towards a strict coupled cluster formalism, one may exploit reference-independent amplitudes provided by (1 + (T) over tilde (m))vertical bar Psi(m)(0)> to define a reference-dependent operator (T) over cap (m) by fitting the eigenvector of the (dressed) CAS-SD CI matrix. The two variants, which are internally uncontracted, give rather similar results. The new MR-CC version has been tested on the ground state potential energy curves of 6 molecules (up to triple-bond breaking) and two excited states. The non-parallelism error with respect to the full-CI curves is of the order of 1 mE(h). Published by AIP Publishing.
机译：Multiexponential Jeziorski-Monkhorst形式主义中的状态特定的多参考耦合簇（MR-CC）的核心难度涉及单一和双激励算子的定义，其出现在指数波运营商中。如果参考空间是完整的有效空间（CAS），则这些幅度的数量大于单独和双重激发的决定簇的数量，其中一个可以将其投射到eigenequation，并且必须施加额外的条件。本工作首先定义了在波浪函数垂直条PSI（m）（0）>的CAS分量上的TINDE（M）上的状态特定的参考操作员（T），最大化（1 +（t ）通过波浪（M））垂直条PSI（M） CAS-SD（单打和双打）配置相互作用（CI）矩阵垂直条PSI（CAS-SD）> I的特征向量。根据中间哈密顿的形式主义，该操作者可用于产生三元和四分之一的近似系数，以及CAS-SD CI矩阵的敷料。该过程可以迭代到收敛。作为对严格的耦合簇形式主义的改进，可以利用（1 +（t）over TILDE（M））垂直杆PSI（M）>以利用（1 +（T））垂直杆PSI（0）>来利用相互独立的幅度来定义参考依赖的操作员（T ）通过拟合（衣服）CAS-SD CI基质的特征向量来通过盖子（m）。两种变体，在内部无核，给予相似的结果。新的MR-CC版本已经过6分子的地位势能曲线（直到三键断裂）和两个激发态。关于全CI曲线的非平行误差是1 me（h）的顺序。通过AIP发布发布。

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