Electronic response to ion projectiles traversing matter from first principles

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• Prof. Emilio Artacho (Cambridge & Nanogune)
• Thursday 09 October 2025, 14:00-15:30
• Seminar Room 3, RDC.

If you have a question about this talk, please contact Bo Peng.

Projectile particles slow down when traversing matter by exciting its electrons. This electronic stopping process has been target of research throughout the last century motivated by its importance in radiation damage in various contexts, mostly in nuclear and aerospace technologies, but also in medical physics. Linear response methods have been very much used since Lindhard contributions in the fifties, given the fact that the effect of such projectiles can be weak if swift enough. They are however not suitable for projectile velocities comparable to those of the target electrons, where the energy can transfer at rates from eV per Angstrom to keV per Angstrom, in a quite strongly out of equilibrium dynamics. The first non-linear theory was proposed at TCM in 1981 for the homogeneous electron liquid. The radiation damage problem in the synthetic rocks proposed for nuclear waste encapsulation prompted our facing the problem for insulators two decades ago. We did it by explicit simulation from first principles: put a projectile particle in a box containing a big enough sample of the material of interest, start moving it, and follow the dynamics of the surrounding electrons. The evolution of the energy offers the electronic stopping power, comparable with experiments, which allow validation of the simulation. We use real-time propagation within time-dependent density-functional theory. Validation has been satisfactory enough in various systems so as to take the simulations with some credibility. The described virtual experiments have allowed us to gain deeper understanding of electronic stopping processes, which has also allowed for furthering the theory in this context. Various results will be presented, as well as theoretical developments prompted by technical issues (e. g. a moving basis set in the calculations induces a gauge field related the curvature of the wave-function manifold, analogous to Berry’s), and a Floquet theory of stopping for crystalline systems. 

This talk is part of the Theory of Condensed Matter series.

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