Molecular g－tensors from analytical response theory and quasi-degenerate perturbation theory in framework of complete active space self-consistent field method
Molecular g－tensors from analytical response theory and quasi-degenerate perturbation theory in framework of complete active space self-consistent field method
复制标题
完整活动空间自洽场方法框架下解析响应理论和准简并微扰理论的分子 g 张量
DOI：
10.1080/00268976.2015.1012128
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
and T. Yanai
中科院分区：
文献类型：
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作者：
T. N. Lan;J. Chalupsky;;and T. Yanai
分子场张量是电子帕拉磁共振（EPR）测量提供的一个重要光谱参数，通常需要用计算方法来解释。在这里，我们提出了两个新的实现的基础上的一阶和二阶微扰理论计算的g-张量的完全活跃的空间自洽场（CASSCF）波函数模型。在一阶方法中，采用准简并微扰理论（QDPT）构造了自旋轨道耦合算符微扰的相对论CASSCF态，并采用我们最近提出的柔性核屏蔽自旋轨道近似，以单电子形式有效地描述了CASSCF态.二阶方法是建立在线性响应理论基础上的一种新方法，它考虑了外磁场的扰动。它是实现与耦合扰动CASSCF（CP-CASSCF）的方法，它提供了一个等效的未截断的sum-over-states扩展。一阶和二阶方法之间的性能的比较显示为各种分子含有轻到重的元素，突出了它们的相对优势和劣势。详细给出了QDPT和CP-CASSCF方法的公式以及Zeeman算子的二阶Douglas-Kroll-Hess图像变换的推导。
The molecularg-tensor is an important spectroscopic parameter provided by electron para magnetic resonance (EPR) measurement and often needs to be interpreted using computational methods. Here, we present two new implementations based on the first-order and second-order perturbation theories to calculate theg-tensors within the complete-active space self-consistent field (CASSCF) wave function model. In the first-order method, the quasi-degenerate perturbation theory (QDPT) is employed for constructing relativistic CASSCF states perturbed with the spin–orbit coupling operator, which is described effectively in one-electron form with the flexible nuclear screening spin–orbit approximation introduced recently by us. The second-order method is a newly reported approach built upon the linear response theory which accounts for the perturbation with respect to external magnetic field. It is implemented with the coupled–perturbed CASSCF (CP-CASSCF) approach, which provides an equivalent of untruncated sum-over-states expansion. The comparison of the performances between the first-order and second-order methods is shown for various molecules containing light to heavy elements, highlighting their relative strength and weakness. The formulations of QDPT and CP-CASSCF approaches as well as the derivation of the second-order Douglas–Kroll–Hess picture change of Zeeman operators are given in detail.