Slow atomic particles interacting with metals (either at surfaces or in bulk) are screened by the medium electrons. The screening is provided by a rearrangement of electronic charge in the vicinity of the projectile. The polarization induced in the metal by the particle strongly depends on the particle charge state. In a typical interaction process, the charge state of the moving particle varies along its trajectory. Electron capture from the target to the ion reduces the charge state of the latter. One of such electron capture mechanisms is the Auger process, in which an electron jumps from the valence band of the metal to an ion bound state. The energy released in such transition is balanced by an electronic excitation in the medium.

We use density functional theory to describe the interaction between atomic particles and free-electron-like metals, the latter represented by a jellium model. We pay particular attention to Auger processes and their charge transfer probabilities. In recent years, a large amount of experimental work has been devoted to study spin effects in the interaction of low velocity spin-polarized He⁺ ions and He^* metastable atoms. We calculate the spin-polarization of electrons emitted in the neutralization of He⁺ ions interacting with metals. All stages of the emission process are included: the spin-dependent perturbation induced by the projectile, the excitation of electrons in Auger neutralization processes, the creation of a cascade of secondaries, and the escape of the electrons through the surface potential barrier. The model allows us to explain in quantitative terms the measured spin-polarization of the yield in the interaction of spin-polarized He⁺ ions with paramagnetic surfaces, and to disentangle the role played by each of the involved mechanisms. We show that electron-electron scattering processes at the surface determine the spin-polarization of the total yield.

Additional efforts to calculate the energy loss of charged particles penetrating metallic media have been made using time-dependent density functional theory. A brief explanation can be found under the 'electron dynamics in metal nanoparticles' link in the 'research' section.