Ab Initio Approach for Exciton Dynamics

We investigate exciton dynamics from first principles by combining our recently developed formalism to compute exciton-phonon (ex-ph) interactions with the Boltzmann transport equation (BTE) to simulate the exciton non-equilibrium dynamics. The computations are challenging – the ex-ph interactions require solving the finite-momentum Bethe Salpeter equation and density functional perturbation theory on fine Brillouin zone grids, and time-stepping the exciton BTE requires a parallel algorithm to explicitly time-step the exciton occupations. We apply our approach to transition metal dichalcogenides, focusing on the time scale for exciton valley decoherence and on exciton transport and relaxation. Our work provides a rigorous framework for computing exciton dynamics in materials from first principles, advancing the understanding of ultrafast excited state dynamics in materials.