Electronic transport properties from first-principles beyond the Boltzmann equation

In this talk we will present some of our efforts for characterizing materials transport properties from first-principles. We first discuss how semiclassical first-principles models are unable to capture the electronic transport properties of Bi₂Se₃, a narrow-gap semiconductor. We show that transport in this material at low doping concentrations is dominated by Zener tunneling, a phenomenon in which carriers tunnel between the valence and the conduction band, rather than diffuse under the action of the electric field. This transport mechanism is here described using a novel first-principles model based on the Wigner distribution. Surprisingly, we find that Zener tunneling is not limited to low-energy carriers, but occurs also between band subvalleys of energy larger than the band gap.  Next, we introduce Phoebe, a new open-source software for computing thermoelectric properties by solving the electron and phonon Boltzmann equations. Phoebe computes electron-phonon and phonon-phonon scattering properties from first-principles simulations, allowing a fully ab-initio prediction of thermoelectric properties. Additionally, we implemented an efficient mixed MPI and OpenMP parallelization and GPU acceleration, allowing us to take advantage of modern computing infrastructure.