An introduction to the Zwanzig–Mori–Götze–Wölfle memory function formalism (or generalized Drude formalism) is presented. This formalism is used extensively in analyzing the experimentally obtained optical conductivity of strongly correlated systems such as cuprates and iron-based superconductors. For a broader perspective both the generalized Langevin equation approach and the projection operator approach for the memory function formalism are given. The Götze–Wölfle perturbative expansion of memory function is presented and its application to the computation of the dynamical conductivity of metals is also reviewed. This digest of the formalism contains all the mathematical details for pedagogical purposes.

中文翻译：

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记忆功能形式主义：概述

介绍了Zwanzig-Mori-Götze-Wölfle记忆函数形式主义（或广义的Drude形式主义）。这种形式主义被广泛用于分析通过实验获得的强相关系统（例如铜酸盐和铁基超导体）的光导率。从更广阔的角度来看，给出了广义朗格文方程方法和用于记忆函数形式主义的投影算子方法。介绍了Götze-Wölfle记忆函数的扰动展开，并综述了其在金属动态电导率计算中的应用。形式主义的摘要包含用于教学目的的所有数学细节。