We present extensive new ab initio path integral Monte Carlo (PIMC) results for an electron gas at warm dense matter conditions that is subject to multiple harmonic perturbations. In addition to the previously investigated nonlinear effects at the original wave number (Dornheim et al., Phys. Rev. Lett., 2020, 125, 085001) and the excitation of higher harmonics (Dornheim et al., Phys. Rev. Res., 2021, 3, 033231), the presence of multiple external potentials leads to mode-coupling effects, which constitute the dominant nonlinear effect and lead to a substantially more complicated density response compared to linear response theory. One possibility to estimate mode-coupling effects from a PIMC simulation of the unperturbed system is given in terms of generalized imaginary-time correlation functions that have been recently introduced by Dornheim et al. (J. Chem. Phys., 2021, 155, 054110). In addition, we extend our previous analytical theory of the nonlinear density response of the electron gas in terms of the static local field correction (Dornheim et al., 2020, Phys. Rev. Lett., 125, 235001), which allows for a highly accurate description of the PIMC results with negligible computational cost.

中文翻译：

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暖致密物质中外部扰动的非线性相互作用

我们针对受多重谐波扰动的暖致密物质条件下的电子气，提出了广泛的新从头算路径积分蒙特卡洛 (PIMC) 结果。除了先前研究的原始波数下的非线性效应（Dornheim 等人，Phys. Rev. Lett.，2020, 125, 085001）和高次谐波的激发（Dornheim 等人，Phys. Rev. Res. , 2021, 3, 033231), 多个外部电势的存在导致模式耦合效应，这构成了主要的非线性效应，并导致比线性响应理论复杂得多的密度响应。根据 Dornheim 等人最近引入的广义虚时间相关函数，给出了一种从未受扰动系统的 PIMC 模拟中估计模式耦合效应的可能性。(J. Chem. Phys., 2021, 155, 054110)。此外，我们在静态局部场校正方面扩展了我们之前关于电子气非线性密度响应的分析理论（Dornheim et al., 2020, Phys. Rev. Lett., 125, 235001），它允许以可忽略的计算成本高度准确地描述 PIMC 结果。