EPIq: An open-source software for the calculation of electron-phonon interaction related properties

EPIq (Electron-Phonon wannier Interpolation over k and q-points) is an open-source software for the calculation of electron-phonon interaction related properties from first principles. Acting as a post-processing tool for a density-functional perturbation theory code (Quantum ESPRESSO) and wannier90, EPIq exploits the localization of the deformation potential in the Wannier function basis and the stationary properties of a force-constant functional with respect to the first-order perturbation of the electronic charge density to calculate many electron-phonon related properties with high accuracy and free from convergence issues related to Brillouin zone sampling. EPIq features include: the adiabatic and non-adiabatic phonon dispersion, superconducting properties (including the superconducting band gap in the Migdal-Eliashberg formulation), double-resonant Raman spectra and lifetime of excited carriers. The possibility to customize most of its input makes EPIq a versatile and interoperable tool. Particularly relevant is the interaction with the Stochastic Self-Consistent Harmonic Approximation (SSCHA) allowing anharmonic effects to be included in the calculation of electron-properties. The scalability offered by the Wannier representation combined with a straightforward workflow and easy-to-read input and output files make EPIq accessible to the wide condensed matter and material science communities.

EPIq（基于k和q点的电子-声子Wannier插值，Electron-Phonon wannier Interpolation over k and q-points）是一款开源软件，可从第一性原理出发计算与电子-声子相互作用相关的各类物理性质。作为密度泛函微扰理论（density-functional perturbation theory）代码Quantum ESPRESSO与wannier90的后处理工具，EPIq依托Wannier函数（Wannier function）基组下形变势的局域特性，以及针对电子电荷密度一阶微扰的力常数泛函的平稳性质，能够高精度计算诸多电子-声子相关物性，且不受布里渊区采样（Brillouin zone sampling）相关收敛问题的困扰。EPIq具备以下特性：绝热与非绝热声子色散（adiabatic and non-adiabatic phonon dispersion）、超导物性（涵盖Migdal-Eliashberg框架下的超导能隙（superconducting band gap））、双共振拉曼光谱（double-resonant Raman spectra）以及载流子激发态寿命（lifetime of excited carriers）。其支持自定义绝大多数输入参数的特性，令EPIq成为一款通用性强、可互操作的工具。尤为值得关注的是，其与随机自洽简谐近似（Stochastic Self-Consistent Harmonic Approximation，SSCHA）的交互功能，可将非简谐效应纳入电子物性的计算流程。依托Wannier表象（Wannier representation）所提供的可扩展性，搭配简洁直观的工作流程与易于解读的输入输出文件，EPIq便于广大凝聚态物理（condensed matter）与材料科学（material science）领域的科研人员使用。