Electronic excitations and their ultrafast real-time dynamics are at the foundation of how we use and probe matter. Recent experimental advances allow us to do so with unprecedented accuracy and time resolution down to the atomistic level, however, interpretation of these experiments requires solid theoretical understanding. This can be provided by first-principles theoretical-spectroscopy, e.g. based on many-body perturbation theory and time-dependent density functional theory. In this talk, I will illustrate recent successful examples for how these electronic-structure methods lead to deep understanding: For methyl-ammonium lead tri-iodide we explain that the line shape of the absorption edge is dominated by Mahan excitons in the presence of free electrons and because of that, it resembles the shape found for the pure material up to large free-electron concentrations. For magnesium oxide under proton irradiation we discover a novel diffusion mechanism arising from hot electrons that we attribute to excitations from a deep intrinsic defect state. This mechanism can potentially be used for ion-beam based sample manipulation at the nanoscale. While such first-principles simulation techniques provide deep insight and allow for predictive accuracy with excellent agreement with experiment, they rely on approximations. In this talk, I will also illustrate our recent efforts of developing better theoretical understanding of dielectric screening physics and how to bridge time scales from ultrafast electron dynamics to atomic diffusion. Finally, I will describe how incorporating information from first-principles simulations that is collected in large, freely available online databases into computational research on excited electronic states can side-step the problem of high computational cost. To this end, we used Materials Project and branch-point energy alignment to facilitate efficient design of semiconductor heterojunctions.

Excited electronic states and ultrafast dynamics: Pushing towards design of materials

2019 Fall National Meeting

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