Abstract

Understanding nonequilibrium quasiparticle dynamics in materials requires going beyond static electronic structure. Here, we present an ab initio framework that combines GW/BSE with real-time quantum dynamics to simulate exciton dynamics in different materials. It is shown that exciton dynamics is fundamentally driven by different many-body interactions. In transition metal dichalcogenides, exchange interaction enables ultrafast valley depolarization by opening intervalley channels forbidden in a single-particle picture. Furthermore, phonons act as a dynamical switch that activates long-range Coulomb coupling, leading to rapid bright-to-dark exciton relaxation. When electron-phonon coupling are strong enough, it can also dress the exciton and form polaron-exciton in polar materials. We reveal the formation of dynamically fluctuating polaron–exciton states in TiO₂, where electron – phonon coupling and Coulomb interaction cooperatively determine the  quasiparticle properties and lifetimes.