Toward Precise Ab Initio Simulations of the Ultrafast Dynamics of Electrons and Phonons

Recent progress in combining density functional theory and related ab initio methods with kinetic equations are enabling spectacular advances in computing carrier dynamics in materials from first principles. We will first review this framework and early ab initio calculations of electron scattering rates and carrier thermalization, and then discuss recent developments. The talk will focus on a numerical approach to evolve in time the coupled Boltzmann transport equations (BTEs) of electrons and phonons, using ab initio electron-phonon and phonon-phonon interactions together with a parallel algorithm to explicitly time step the BTEs. Our approach can simulate the electron and phonon dynamics up to hundreds of picoseconds (with a femtosecond time resolution), and the accuracy of the interactions used in the calculations can be validated by computing transport properties. We show example calculations on graphene and semiconductors, for which we compute carrier cooling rates, mode-resolved phonon dynamics, transient absorption, and time-resolved structural snapshots and diffuse X-ray scattering. We will show how this approach can be extended to include excitons, by discussing calculations of exciton-phonon interactions and real-time exciton dynamics. We will outline code development efforts, open problems and future directions.