Many recent developments in the area of multistate multireference perturbation theories focused on methods that use a state-averaged 0th order Hamiltonian. We recently found that the dynamic correlation dressed complete active space method fails in describing ligand field and charge transfer states in a balanced way precisely because it uses a state-averaged 0th order Hamiltonian [L. Lang and F. Neese, J. Chem. Phys. 150, 104104 (2019)]. The multipartitioning idea allows the use of state-specific 0th order Hamiltonians in a multistate framework and could therefore alleviate the mentioned problem. However, the effective Hamiltonian is non-Hermitian in the traditional formulation of multipartitioning, which can lead to unphysical behavior, especially for nearly degenerate states. In order to achieve a more balanced treatment of states with different physical character and at the same time have a Hermitian effective Hamiltonian, we combine in this work multipartitioning with canonical Van Vleck perturbation theory. At the 2nd order, the result is a Hermitian variant of multipartitioning quasidegenerate N-electron valence state perturbation theory. The effect of model space noninvariance of the method is discussed and the benefit of a Hermitian formulation is highlighted with numerical examples. The method is shown to give good results for the calculation of electronic transitions of the [CuCl4]2 -complex and for the calculation of electron paramagnetic resonance parameters, which are two examples where the balance between ligand field and charge transfer configurations is of utmost importance.

中文翻译：

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哈密​​顿量的多重划分与范式Vleck规范扰动理论的结合导致了准生成N电子价态扰动理论的Hermitian变体。

多状态多参考摄动理论领域的许多最新发展集中在使用状态平均0阶哈密顿量的方法上。最近，我们发现动态相关修饰完全有源空间方法无法精确地描述配体场和电荷转移状态，因为它使用状态平均的0阶哈密顿量[L. Lang和F. Neese，化学杂志。物理 150，104104（2019）]。多分区思想允许在多状态框架中使用特定于状态的0阶哈密顿量，因此可以缓解上述问题。但是，在传统的多分区公式中，有效的哈密顿量不是非厄密量，这会导致非物理行为，尤其是对于几乎退化的状态。为了对具有不同物理特性的状态实现更平衡的处理，并同时具有厄米有效的哈密顿量，我们在这项工作中结合了范格维克规范扰动理论进行多分区。在2阶上，结果是多重划分的准生成N电子价态微扰理论的Hermitian变体。讨论了该方法的模型空间不变性的影响，并通过数值示例突出了Hermitian公式的好处。结果表明，该方法为计算[CuCl4] 2-配合物的电子跃迁和计算电子顺磁共振参数提供了良好的结果，这是两个例子，其中配体场和电荷转移构型之间的平衡至关重要。 。