The influence of trajectories and pseudization on first-principles calculations of electronic stopping in warm dense matter

Scarce experimental data for ion transport in warm dense matter makes first-principles results valuable benchmarks for simpler models. However, high computational costs typically limit first-principles studies to temperatures below ~10 eV and make it difficult to characterize sensitivities to various approximations. We use time-dependent density functional theory to compute electronic stopping powers of protons in warm dense deuterium, carbon, and aluminum at densities up to 10 g/cc and temperatures up to 20 eV. We define a metric to quantify sampling errors caused by finite proton trajectories and find that comparably faithful trajectories lead to average stopping powers that do not depend on ion temperature for materials out of thermal equilibrium. On the other hand, we see a strong dependence on electronic temperature in some cases: heating solid-density aluminum from 1 eV to 20 eV reduces the Bragg peak by ~30% and shifts it toward ~50% higher velocities. Comparing results computed with different pseudization schemes reveals competing effects within the contributions of bound and free electrons. This work guides improvements to much more efficient stopping models based on average atom methods.