Benchmark calculations of electronic stopping power in warm dense matter using time-dependent density functional theory

Scarcity of experimental data in the warm dense regime makes first-principles calculations particularly valuable for constraining tabulated data and characterizing limitations of more efficient models. Real-time time-dependent density functional theory (TDDFT), which can capture mean-field excited electron dynamics in extended systems, ranks among the most accurate but computationally intensive methods of predicting electronic stopping powers. However, TDDFT calculations still involve various choices and approximations contributing to uncertainties in computed values. For the case of alpha particle stopping in warm dense hydrogen, we cross-benchmark different TDDFT codes and methodologies, demonstrate reproducibility, and scrutinize best practices. We then consider effects that may challenge more approximate stopping power models, including nonlinear behavior manifesting as deviations from Z² scaling between proton and alpha stopping in carbon and aluminum and the validity of additivity laws for proton stopping in carbon-deuterium and carbon-hydrogen mixtures. This work takes important steps toward reducing uncertainties in first-principles stopping power predictions and improving the accuracy of more efficient treatments.