Modeling time-resolved kinetics in solids induced by extreme electronic excitation

TL;DR

This paper introduces a combined Monte Carlo and molecular dynamics simulation approach to model the time-resolved atomic and electronic response of solids to extreme electronic excitation, enabling detailed analysis of energy transfer processes.

Contribution

The paper presents a novel on-the-fly MC-MD method that efficiently models nonthermal effects and atomic dynamics during electronic excitation in solids, with validation against tight-binding MD.

Findings

Accurately describes atomic dynamics after X-ray irradiation.

Efficiently models nonthermal electron-atom energy transfer.

Provides insights into energy deposition from nonequilibrium electronic systems.

Abstract

We present a concurrent Monte Carlo (MC) - molecular dynamics (MD) approach to modeling of matter response to excitation of its electronic system. The two methods are combined on-the-fly at each time step in one code, TREKIS-4. The MC model describes arrival of irradiation, which in the current implementation can consist of a photon, an electron, or a fast ion. It also traces induced cascades of excitation of secondary particles, electrons and holes, and their energy exchange with atoms due to scattering. The excited atomic system is simulated with an MD model. We propose a simple and efficient way to account for nonthermal effects in the electron-atom energy transfer in covalent materials via conversion of potential energy of the ensemble into the kinetic energy of atoms, which can be straightforwardly implemented into an MD simulation. Such a combined MC-MD approach enables us time-resolved tracing of the excitation kinetics of both, electronic and atomic systems, and their simultaneous response to a deposited dose. As a proof-of-principle example, we show that proposed method describes atomic dynamics after X-ray irradiation in a good agreement with tight-binding MD, with much more affordable computational demands. The new model also allows us to gain insights into behavior of the atomic system during the energy deposition from a nonequilibrium electronic system excited by an ion impact.