Ab Initio Calculations of Nonequilibrium Coupled Carrier and Phonon Dynamics

The dynamics and equilibration of coupled excited electrons and phonons is important for understanding novel electronics and time-resolved spectroscopy. Nonequilibrium distributions of electrons and phonons coupled through electron-phonon and phonon-phonon interactions can be described within the framework of the Boltzmann transport equation (BTE). Here, we compute from first principles the scattering and coupled ultrafast dynamics of nonequilibrium electrons and phonons by simultaneously time-stepping the electron and phonon BTEs using a fourth-order Runge Kutta scheme. Numerical and parallelization schemes are discussed in detail. Our approach is applied to graphene and silicon, where analysis of the time-dependent electron and mode-resolved phonon distributions provides unprecedented insight into the equilibration process of excited electrons.