发表机构
Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin; Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校奥登计算工程与科学研究所; 德克萨斯大学奥斯汀分校物理系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出一种第一性原理方法，可计算任意阶非线性电子-声子相互作用，并证明二阶耦合对极化子性质至关重要，为超越线性近似的研究奠定基础。
AI 中文摘要
电子-声子相互作用是多种现象的基础，涵盖输运、超导、极化子以及超快载流子动力学。尽管这是凝聚态物理中研究最深入的课题之一，但关于电子-声子物理的研究大多集中于线性的一阶耦合。二阶及更高阶的非线性耦合通常被忽略，因为其计算要求过高，且我们缺乏能够同时提供对角和非对角耦合矩阵元的计算框架。在本工作中，我们报告了一种用于计算真实材料中任意阶非线性电子-声子相互作用的理论和计算方法。我们的方法结合了电子波函数的单胞计算和声子微扰的超胞计算的优点，具有系统可改进性，可用于半局域或非局域交换关联泛函，并适用于Wannier-Fourier插值。作为第一个概念验证，我们通过计算金刚石、氟化锂和石墨中的二阶电子-声子耦合矩阵元来展示该方法，这三种材料分别代表非极性半导体、极性半导体和金属。此外，我们将从头算极化子方程推广到二阶电子-声子耦合，并表明二阶耦合对于在极化子形成能和跳跃势垒中实现定量精度至关重要。本方法将应用于目前在线性电子-声子耦合近似下研究的所有性质和现象，包括声子介导的超导、激发态动力学，以及谐波和非谐波系统。
英文摘要
Electron-phonon interactions underpin a variety of phenomena, ranging from transport and superconductivity to polarons and ultrafast carrier dynamics. Despite being one of the most intensely studied subjects in condensed matter physics, research on electron-phonon physics mostly focused on linear, first-order couplings. Second- and higher-order nonlinear couplings are commonly ignored because their calculations are too demanding and we lack computational frameworks that can provide both diagonal and off-diagonal coupling matrix elements. In this work, we report a theory and computational method for computing nonlinear electron-phonon interactions of any order in real materials. Our approach combines the advantages of unit-cell calculations of electron wavefunctions and supercell calculations of phonon perturbations, is systematically improvable, can be used with either semilocal or nonlocal exchange-correlation functionals, and is amenable to Wannier-Fourier interpolation. As a first proof of concept, we illustrate this method by computing second-order electron-phonon coupling matrix elements in diamond, lithium fluoride, and graphite as representative nonpolar semiconductors, polar semiconductors, and metals, respectively. Furthermore, we generalize the ab initio polaron equations to second-order electron-phonon couplings, and we show that second-order couplings are essential to achieve quantitative accuracy in polaron formation energies and hopping barriers. The present methodology will find application in the study of all properties and phenomena that are currently being investigated within the linear electron-phonon coupling approximation, from phonon-mediated superconductivity to excited-states dynamics, both in harmonic and anharmonic systems.
