Quantum dynamics of excited states is critically important in many materials such as photovoltaic solar energy harvesters, photocatalysts, molecular electronics systems, or photo-actuated molecular switches. Electron-hole recombination, interfacial charge transfer, or nonradiative excitation energy relaxation, all require accounting for nonadiabatic (NA) effects. Computational modeling of NA and quantum dynamics (NA/QD) at the atomistic level can provide valuable insights into the mechanisms and kinetics of these processes and help design new materials with desired properties. The NA/QD modeling of nanoscale systems is computationally taxing. As a result, the timescales accessible to a typical direct simulation of the dynamics are limited to a few picoseconds and the system sizes do not excessed a few hundred atoms.<br/>In this talk, I will present our recent developments aimed to extend the timescales of NA/QD simulations and enable handling systems containing as much as several thousands of atoms. Our focus will be on the techniques for NA/QD modeling in nanoscale and condensed-matter systems, where electron-nuclear back-reaction can be neglected and notable methodological simplifications can be made. Working within this framework, I will introduce our time-domain machine-learning (TD-ML) methodology that can be applied to both model and atomistic systems. As an example, the unprecedentedly long NA/QD simulation of electron-hole recombination in monolayer black phosphorus will be demonstrated. A brief assessment of alternative technique based on repetition of short-time trajectories will be briefly discussed. As a way to extend the size of the modeled systems, I will showcase the recently developed NA/QD methodology based on the extended tight-binding density functional (xTB) approach. The applications of such a technique to the largest ever-considered atomistic models of Si nanoclusters and graphitic carbon nitride (C3N4) monolayers will be discussed. With the latter example, I will also discuss the dependence of electron-hole recombination timescales on the concentration of charge carriers.

Bigger and longer: Extending the size and timescales of nonadiabatic dynamics simulations in solar energy materials

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