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.Program summaryProgram Title: EPIqCPC Library link to program files: https://doi .org /10 .17632 /f2syws66d7 .1Developer's repository link: https://gitlab .com /the -epiq-team /epiq Licensing provisions: GPLv3Programming language: FORTRAN95External routines: BLAS (http://www /netlib .org /blas), LAPACK (http://www .netlib .org /lapack), Quantum ESPRESSO (https://www .quantum -espresso .org/), wannier90 (https://wannier .org/)Nature of problem: Direct first principles calculation of quantities obtained via linear response methods in solid-state systems, such as the deformation potential, can be computationally demanding, hindering proper convergence.Solution method: An interpolation scheme exploiting 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 is implemented in EPIq. Within this approach it is possible to calculate many electron-phonon related properties with high accuracy and a low computational effort.