  Over the past decade, experimental microscopy and spectroscopy have made
significant progress in the study of the morphological, optical, electronic and
transport properties of materials. These developments include higher spatial
resolution, shorter acquisition times, more efficient monochromators and
electron analysers, improved contrast imaging and advancements in sample
preparation techniques. These advances have driven the need for more accurate
theoretical descriptions and predictions of material properties. Computer
simulations based on first principles and Monte Carlo methods have emerged as a
rapidly growing field for modeling the interaction of charged particles, such
as electron, proton and ion beams, with various systems, such as slabs,
nanostructures and crystals. This report delves into the theoretical and
computational approaches to modeling the physico-chemical mechanisms that occur
when charged beams interact with a medium. These mechanisms encompass single
and collective electronic excitation, ionization of the target atoms and the
generation of a secondary electron cascade that deposits energy into the
irradiated material. We show that the combined application of ab initio
methods, which are able to model the dynamics of interacting many-fermion
systems, and Monte Carlo methods, which capture statistical fluctuations in
energy loss mechanisms by random sampling, proves to be an optimal strategy for
the accurate description of charge transport in solids. This joint quantitative
approach enables the theoretical interpretation of excitation, loss and
secondary electron spectra, the analysis of the chemical composition and
dielectric properties of solids and contributes to our understanding of
irradiation-induced damage in materials, including those of biological
significance.
