Assessing the quality of relaxation-time approximations with fully-automated computations of phonon-limited mobilities

TL;DR

This paper evaluates the accuracy of common relaxation-time approximations in phonon-limited mobility calculations by comparing them with exact iterative solutions, highlighting significant deviations and advocating for more reliable methods.

Contribution

Developed an automated high-throughput workflow to compute and compare phonon-limited mobilities, revealing the unreliability of traditional approximations.

Findings

Approximate methods can significantly deviate from exact solutions.

Exact iterative solutions are computationally feasible and more reliable.

Many prior results using approximations may be inaccurate.

Abstract

The mobility of carriers, as limited by their scattering with phonons, can now routinely be obtained from first-principles electron-phonon coupling calculations. However, so far, most computations have relied on some form of simplification of the linearized Boltzmann transport equation based on either the self-energy, the momentum- or constant relaxation time approximations. Here, we develop a high-throughput infrastructure and an automatic workflow and we compute 69 phonon-limited mobilities in semiconductors. We compare the results resorting to the approximations with the exact iterative solution. We conclude that the approximate values may deviate significantly from the exact ones and are thus not reliable. Given the minimal computational overhead, our work encourages to rely on this exact iterative solution and warns on the possible inaccuracy of earlier results reported using relaxation time approximations.