Ultrafast dynamics of coupled electrons, phonons and excitons from first principles*

Combining density functional theory and related methods with kinetic equations has enabled remarkable advances in computing the ultrafast dynamics of materials from first principles. After reviewing this framework, I will present 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 coupled electron and phonon dynamics up to tens of picoseconds (with a femtosecond time resolution) and its quantitative accuracy can be validated by computing transport properties. Using graphene as a case study, I will demonstrate calculations of coupled ultrafast carrier and phonon population dynamics, and simulations of time-resolved transient absorption, structural snapshots, and diffuse X-ray scattering. Extensions to include excitonic effects will also be discussed, focusing on calculations of exciton-phonon interactions and real-time exciton dynamics in two-dimensional materials. Code development efforts and future directions will be outlined.