Inelastic scattering of electrons in water from first principles: cross sections and inelastic mean free path for use in Monte Carlo track-structure simulations of biological damage

Abstract

Modelling the inelastic scattering of electrons in water is fundamental, given their crucial role in biological damage. In Monte Carlo track-structure codes used to assess biological damage, the energy loss function, from which cross sections are extracted, is derived from different semiempirical optical models. Extrapolations are normally used to extend the available optical data for q = 0. At low energies, results are sensitive to the differences in the optical models used to extrapolate the energy loss function. In this work, we present ab-initio linear-response timedependent density functional theory calculations of the energy loss function of liquid water. Our results are in good agreement with experimental data both in the optical limit and for finite values of the momentum transfer. Inelastic scattering cross sections, inelastic mean free paths, and electronic stopping powers are also presented in comparison with recent semi-empirical calculations and experimental data. Moreover, we provide an in-depth analysis of the contributions of different molecular orbitals, species, and orbital angular momenta to the total energy loss function. Finally, we present single-differential cross sections computed for each molecular orbital channel, which should prove useful for Monte-Carlo track-structure simulations.