Ragot Sébastien, Becker Pierre J
Laboratoire Structure, Propriété Modélisation des Solides (CNRS, Unité Mixte de Recherche 85-80), Ecole Centrale Paris, Grande Voie des Vignes, 92295 Chatenay-Malabry, France.
J Chem Phys. 2006 Oct 21;125(15):154109. doi: 10.1063/1.2358977.
Empirically correlated density matrices of N-electron systems are investigated. Closed-form expressions are derived for the one- and two-electron reduced density matrices from a pairwise correlated wave function. Approximate expressions are then proposed which reflect dispersive interactions between closed-shell centrosymmetric subsystems. Said expressions clearly illustrate the consequences of second-order correlation effects on the reduced density matrices. Application is made to a simple example: the He(2) system. Reduced density matrices are explicitly calculated, correct to second order in correlation, and compared with approximations of independent electrons and independent electron pairs. The models proposed allow for variational calculations of interaction energies and equilibrium distance as well as a clear interpretation of dispersive effects on electron distributions. Both exchange and second order correlation effects are shown to play a critical role on the quality of the results.
研究了N电子系统的经验相关密度矩阵。从成对相关波函数导出了单电子和双电子约化密度矩阵的闭式表达式。然后提出了反映闭壳中心对称子系统之间色散相互作用的近似表达式。所述表达式清楚地说明了二阶相关效应在约化密度矩阵上的结果。应用于一个简单的例子：He(2)系统。明确计算了相关二阶精度的约化密度矩阵，并与独立电子和独立电子对的近似结果进行了比较。所提出的模型允许对相互作用能和平衡距离进行变分计算，并能清晰地解释色散效应在电子分布上的作用。交换效应和二阶相关效应都被证明对结果的质量起着关键作用。
