Carrier mobility of strongly anharmonic materials from first principles

First-principles approaches for phonon-limited electronic transport are typically based on many-body perturbation theory and transport equations. With that, they rely on the validity of the quasiparticle picture for electrons and phonons, which is known to fail in strongly anharmonic systems. In this work, we demonstrate the relevance of effects beyond the quasiparticle picture by combining ab initio molecular dynamics and the Kubo-Greenwood (KG) formalism to establish a nonperturbative, stochastic method to calculate carrier mobilities while accounting for all orders of anharmonic and electron-vibrational couplings. In particular, we propose and exploit several numerical strategies that overcome the notoriously slow convergence of the KG formalism for both electronic and nuclear degrees of freedom in crystalline solids. The capability of this method is demonstrated by calculating the temperature-dependent electron mobility of the strongly anharmonic oxide perovskites SrTiO3 and BaTiO3 across a wide range of temperatures. We show that the temperature dependence of the mobility is largely driven by anharmonic, higher-order coupling effects and rationalize these trends in terms of the nonperturbative electronic spectral functions.