This paper presents a unified method for formulating a field-theoretic perturbation theory that encompasses the conventional liquid state theory. First, the free-energy functional of an instantaneous correlation field is obtained from the functional-integral representation of the grand potential. Next, we demonstrate that the instantaneous free-energy functional yields a closure relation between the correlation functions in the mean-field approximation. Notably, the obtained closure relation covers a variety of approximate closures introduced in the liquid state theory.

中文翻译：

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液体中瞬时相关场的自由能功能：封闭物的场论推导。

本文提出了一种统一的方法，用于公式化包含传统液态理论的场论微扰理论。首先，从大势的功能积分表示获得瞬时相关场的自由能功能。接下来，我们证明了瞬时自由能函数在平均场近似中产生了相关函数之间的闭合关系。值得注意的是，所获得的封闭关系涵盖了液态理论中引入的各种近似封闭。