Exchange Coupling Interactions from the Density Matrix Renormalization Group and N-Electron Valence Perturbation Theory: Application to a Biomimetic Mixed-Valence Manganese Complex.
Exchange Coupling Interactions from the Density Matrix Renormalization Group and N-Electron Valence Perturbation Theory: Application to a Biomimetic Mixed-Valence Manganese Complex.
复制标题
密度矩阵重正化群和 N 电子价态微扰理论的交换耦合相互作用：在仿生混合价锰络合物中的应用。
DOI：
10.1021/acs.jctc.7b01035
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发表时间：
2018
影响因子：
5.5
通讯作者：
D. Pantazis
中科院分区：
文献类型：
--
作者：
Michael Roemelt;V. Krewald;D. Pantazis
寡核交换耦合过渡金属配合物中磁能级能量学的准确描述仍然是量子化学面临的巨大挑战。密度矩阵重正化群 (DMRG) 通过使用前所未有的大活动空间，首次使此类系统能够轻松地使用多参考波函数方法。但这是否能保证预测能力的系统性提高？如果可以，是在什么条件下？我们使用经过实验表征的混合价双-μ-氧代/μ-乙酸根 Mn(III,IV) 二聚体（光系统 II 的放氧复合物模型）作为测试系统，确定了 DMRG 使用中的操作参数。全金属3d和桥2p轨道的完整活性空间被证明是最小的有意义的起点；这可以通过 DMRG 轻松实现，并极大地改善了不切实际的纯金属构型相互作用或完整的活性空间自洽场 (CASSCF) 值。轨道优化对于稳定反铁磁态至关重要，而需要对所有涉及的自旋态采用状态平均方法，以避免人为偏离与特定状态计算相关的各向同性行为。选择性包含局部轨道子空间可以探测不同配体和不同超交换途径的相对贡献。然而，总体而言，由于动态相关性恢复不足，全价 DMRG-CASSCF 计算无法提供交换耦合的定量描述。通过 DMRG 实施二阶 N 电子价态微扰理论 (NEVPT2) 并结合全价金属和配体活性空间，可以获得定量准确的结果。讨论了 DMRG-CASSCF/NEVPT2 在寡核簇中交换耦合的未来应用前景。
The accurate description of magnetic level energetics in oligonuclear exchange-coupled transition-metal complexes remains a formidable challenge for quantum chemistry. The density matrix renormalization group (DMRG) brings such systems for the first time easily within reach of multireference wave function methods by enabling the use of unprecedentedly large active spaces. But does this guarantee systematic improvement in predictive ability and, if so, under which conditions? We identify operational parameters in the use of DMRG using as a test system an experimentally characterized mixed-valence bis-μ-oxo/μ-acetato Mn(III,IV) dimer, a model for the oxygen-evolving complex of photosystem II. A complete active space of all metal 3d and bridge 2p orbitals proved to be the smallest meaningful starting point; this is readily accessible with DMRG and greatly improves on the unrealistic metal-only configuration interaction or complete active space self-consistent field (CASSCF) values. Orbital optimization is critical for stabilizing the antiferromagnetic state, while a state-averaged approach over all spin states involved is required to avoid artificial deviations from isotropic behavior that are associated with state-specific calculations. Selective inclusion of localized orbital subspaces enables probing the relative contributions of different ligands and distinct superexchange pathways. Overall, however, full-valence DMRG-CASSCF calculations fall short of providing a quantitative description of the exchange coupling owing to insufficient recovery of dynamic correlation. Quantitatively accurate results can be achieved through a DMRG implementation of second order N-electron valence perturbation theory (NEVPT2) in conjunction with a full-valence metal and ligand active space. Perspectives for future applications of DMRG-CASSCF/NEVPT2 to exchange coupling in oligonuclear clusters are discussed.