Toward precise simulations of the coupled ultrafast dynamics of electrons and atomic vibrations in materials

TL;DR

This paper introduces a first-principles, high-resolution simulation method for tracking coupled electron and phonon dynamics in materials over tens of picoseconds, providing detailed insights into ultrafast processes.

Contribution

It develops a novel, accurate simulation approach combining electron-phonon and phonon-phonon interactions to model ultrafast dynamics with femtosecond resolution.

Findings

Successfully simulated ultrafast electron and phonon dynamics in graphene.

Provided detailed insights into scattering mechanisms and transient optical responses.

Enabled structural and scattering pattern predictions for excited materials.

Abstract

Ultrafast spectroscopies can access the dynamics of electrons and nuclei at short timescales, shedding light on nonequilibrium phenomena in materials. However, development of accurate calculations to interpret these experiments has lagged behind as widely adopted simulation schemes are limited to sub-picosecond timescales or employ simplified interactions lacking quantitative accuracy. Here we show a precise approach to obtain the time-dependent populations of nonequilibrium electrons and atomic vibrations (phonons) up to tens of picoseconds, with a femtosecond time resolution. Combining first-principles electron-phonon and phonon-phonon interactions with a parallel numerical scheme to time-step the coupled electron and phonon Boltzmann equations, our method provides unprecedented microscopic insight into scattering mechanisms in excited materials. Focusing on graphene as a case study, we demonstrate calculations of ultrafast electron and phonon dynamics, transient optical absorption, structural snapshots and diffuse X-ray scattering. Our first-principles approach paves the way for quantitative atomistic simulations of ultrafast dynamics in materials.