n-electron valence state perturbation theory:: A spinless formulation and an efficient implementation of the strongly contracted and of the partially contracted variants
n-electron valence state perturbation theory:: A spinless formulation and an efficient implementation of the strongly contracted and of the partially contracted variants
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DOI：
10.1063/1.1515317
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发表时间：
2002-11-22
影响因子：
4.4
通讯作者：
Malrieu, JP
中科院分区：
文献类型：
--
作者：
Angeli, C;Cimiraglia, R;Malrieu, JP
n -电子价态微扰理论在无自旋形式体系中被重新表述，重点关注“强收缩”和“部分收缩”变体。新的表述基于在激发算符的未微扰态中引入平均值，这些平均值与扩展的库普曼斯定理和运动方程技术中出现的类似平均值相似。如果在活性轨道空间中未微扰的四粒子无自旋密度矩阵是可用的，那么这些辅助量就可以在一开始就被计算出来，它们能够非常高效地计算能量的二阶微扰贡献。一个关于强收缩和部分收缩版本之间相同类型的二阶能量贡献的显著不等式被证明是成立的。讨论了一个关于成功计算Cr₂分子势能曲线的例子。（C）2002美国物理学会
The n-electron valence state perturbation theory is reformulated in a spin-free formalism, concentrating on the "strongly contracted" and "partially contracted" variants. The new formulation is based on the introduction of average values in the unperturbed state of excitation operators which bear resemblance with analogous ones occurring in the extended Koopmans' theorem and in the equations-of-motion technique. Such auxiliary quantities, which allow the second-order perturbation contribution to the energy to be evaluated very efficiently, can be calculated at the outset provided the unperturbed four-particle spinless density matrix in the active orbital space is available. A noticeable inequality concerning second-order energy contributions of the same type between the strongly and partially contracted versions is proven to hold. An example concerning the successful calculation of the potential energy curve for the Cr-2 molecule is discussed. (C) 2002 American Institute of Physics.