Ultrafast irradiation of matter induces a variety of processes in both electronic and atomic systems, intricately affecting each other. To model photoabsorption, nonequilibrium electron kinetics, decays of atomic holes, energy exchange with atoms of the target, nonthermal modification of interatomic potential, and induced atomic dynamics need to be accounted for to understand ensuing damage, the standard practice is to employ hybrid (combined, multiscale) methods. We discuss two examples of such models: XTANT-3 [1] and TREKIS-4 [2]. XTANT-3 combines Monte Carlo (MC), tight-binding molecular dynamics (MD), and Boltzmann collision integrals. It models nonequilibrium electron cascades (only in time), evolution of electronic structure, nonthermal melting, electron-phonon coupling [3], but limited to a few 100-1000s atoms. TREKIS-4 combines MC with classical MD, tracing electronic cascades in space (1d, 2d, or 3d), including relativistic energies. Classical MD models ~10^4-10^5 of atoms, approximately including nonthermal effects in covalent materials, but cannot trace evolution of the electronic structure and interatomic potential.
[1] N. Medvedev, et al., 4open. 1 (2018) 3.
[2] N. Medvedev, et al., Adv. Theory Simulations. (2022) 2200091.
[3] N. Medvedev, J. Phys. Condens. Matter. 32 (2020) 435401.
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