The elphbolt ab initio solver for the coupled electron-phonon Boltzmann transport equations

TL;DR

elphbolt is a modern Fortran code that efficiently solves coupled electron-phonon Boltzmann equations from first principles, enabling detailed analysis of non-equilibrium transport phenomena in materials.

Contribution

It introduces a self-consistent, symmetry-exploiting implementation of coupled electron-phonon transport equations using first-principles data, with efficient parallelization.

Findings

Accurately captures phonon drag effects on electronic transport.

Calculates thermoelectric coefficients considering electron-phonon interactions.

Demonstrates efficient sampling of fine wave vector meshes.

Abstract

elphbolt is a modern Fortran (2018 standard) code for efficiently solving the coupled electron-phonon Boltzmann transport equations from first principles. Using results from density functional and density functional perturbation theory as inputs, it can calculate the effect of the non-equilibrium phonons on the electronic transport (phonon drag) and non-equilibrium electrons on the phononic transport (electron drag) in a fully self-consistent manner and obeying the constraints mandated by thermodynamics. It can calculate the lattice, charge, and thermoelectric transport coefficients for the temperature gradient and electric fields, and the effect of the mutual electron-phonon drag on these transport properties. The code fully exploits the symmetries of the crystal and the transport-active window to allow the sampling of extremely fine electron and phonon wave vector meshes required for accurately capturing the drag phenomena. The coarray feature of modern Fortran, which offers native and convenient support for parallelization, is utilized. The code is compact, readable, well-documented, and extensible by design.