First-Principles Electronic Stopping and Non-Adiabatic Electron Dynamics in Solids and Liquids

Ion beam analysis techniques rely fundamentally on precise energy-loss description to convert measured energy spectra into accurate depth profiles and quantitative chemical composition. Despite decades of progress, most practical applications still depend on semi-empirical stopping models. The predictive power of such models is limited when applied to materials where electronic stopping is strongly influenced by chemical bonding, crystal structure, or local electronic properties, and when the ions move with low velocities.

To address the above mentioned limitations and the ways to overcome them, this talk evaluates the predictive capabilities of ab initio electronic structure methods to resolve material-specific electronic responses beyond simple homogeneous electron gas approximations. Time-dependent density functional theory (TDDFT), in both linear-response (LR) and real-time (RT) formulations, has opened the way for the predictive first-principles description of non-adiabatic processes in solid-state and liquid targets under external perturbations such as energetic ions and electromagnetic fields. LR-TDDFT gives access to ion-beam-analysis relevant quantities such as inelastic mean free path and scattering cross-sections. RT-TDDFT, on the other hand, allows for an accurate modeling of non-linear electronic response, as well as studying the role of crystallographic orientation and channeling effects in electronic stopping, which cannot be captured within isotropic or trajectory-averaged models.

The applicability of TDDFT will be demonstrated on the examples of different materials, from elemental and compound semiconductors (Ge, GaAs) [1] relevant for technological applications to liquid water [2,3] as a benchmark system for radiation therapy. Finally, I will briefly discuss the TDDFT modeling of laser-matter interaction [4] which is of importance for next-generation surface analysis techniques such as femtosecond laser depth profiling and laser-induced breakdown spectroscopy (LIBS).

I will also discuss recent progress in extensions combining TDDFT with macroscopic and semi-classical descriptions, including two-temperature model (TTM) [5] and dielectric-response-based approaches (Penn model) [6], enabling access to experimentally relevant length and time scales.

References.
[1] Ab initio electronic stopping power for protons in Ga0.5In0.5P/GaAs/Ge triple-junction solar cells for space applications. N. E. Koval, F. Da Pieve, and E. Artacho. R. Soc. Open Sci. 7(11) (2020) 200925.
[2] 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. N. E. Koval, P. Koval, F. Da Pieve, J. Kohanoff, E. Artacho, and D. Emfietzoglou. R. Soc. Open Sci. 9(5) (2022) 212011.
[3] Nonlinear electronic stopping of negatively-charged particles in liquid water. N. E. Koval, F. Da Pieve, B. Gu, D. Muñoz-Santiburcio, J. Kohanoff, and E. Artacho. Phys. Rev. Research 5 (2023) 033063.
[4] Ab initio insights into plasmonic and strong-field contributions to H2 dissociation on silver nanoshells. N. E. Koval, J. I. Juaristi, and M. Alducin. Phys. Chem. Chem. Phys. (2026) Advance Article. & Strong-field effects in the photo-induced dissociation of the hydrogen molecule on a silver nanoshell. N. E. Koval, J. I. Juaristi, and M. Alducin. Chem. Sci. 15(44) (2024) 18581-18591.
[5] Effect of electronic stopping in molecular dynamics simulations of collision cascades in gallium arsenide. J. L. Teunissen, T. Jarrin, N. Richard, N. E. Koval, D. Muñoz Santiburcio, J. Kohanoff, E. Artacho, F. Cleri, and F. Da Pieve. Phys. Rev. Materials 7(2) (2023) 025404.
[6] Stopping cross sections for protons across different phases of water. F. Matias, N. E. Koval, P. de Vera, R. Garcia-Molina, I. Abril, J. M. B. Shorto, H. Yoriyaz, J. J. N. Pereira, T. Fiorini da Silva, M. H. Tabacniks, M. Vos, and P. L. Grande. Phys. Rev. Lett. 135(14) (2025) 148003.