Combined model of the material excitation and relaxation in swift heavy ion tracks

A multiscale approach describing material excitation in the nanometric track of a swift heavy ion (SHI) decelerated in a solid in the electronic stopping regime is presented. This model consists of a combination of three different methods: (a) Monte Carlo simulations of excitation of the electron subsystem of a solid at the femtosecond scale due to scatterings of a SHI and generated fast electrons; (b) a molecular-kinetic approach describing the spatial spreading of electrons after finishing of ionization cascades up to timescales of a hundred femtoseconds; and (c) molecular dynamics simulations of reaction of the lattice on the excess energy transferred from the relaxing electron subsystem at the picosecond time scale. The dynamic structure factor (DSF) formalism links together all these methods. It takes into account effects of spatial and temporal correlations in the atomic system of a target during its interaction with excited electrons in an ion track. For LiF crystals a good agreement is demonstrated between track heating estimated from the experimental data and that predicted by the model.