关联密度矩阵的封闭形式表达式：色散相互作用的应用和（He）2的例子
Closed-form expressions for correlated density matrices: application to dispersive interactions and example of (He)2
摘要：
研究了N电子系统的经验相关密度矩阵。精确的封闭形式的表达式推导出一个和两个电子约化密度矩阵从一般的成对相关波函数。提出了反映闭壳层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对约化密度矩阵的影响。应用程序是一个简单的例子：（He）2系统。减少密度矩阵明确计算，正确的相关性，二阶近似的独立电子和独立的电子对。所提出的模型可以变分计算相互作用能和平衡距离，并清楚地解释色散对电子分布的影响。交换和二阶相关效应被证明对结果的质量起着至关重要的作用。
英文摘要：
Empirically correlated density matrices of N-electron systems are investigated. Exact closed-form expressions are derived for the one- and two-electron reduced density matrices from a general pairwise correlated wave function. Approximate expressions are proposed which reflect dispersive interactions between closed-shell centro-symmetric 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.
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