Ab-initio calculation of electron-ion relaxation in warm dense plasmas

The rapidly growing ability to form and probe warm dense matter (WDM) conditions increases the demand for a quantitative predictive modeling of the non-equilibrium processes induced in the target materials. In particular, much uncertainty remains in our understanding of the electron-ion (e-i) energy relaxation timescales as illustrated by the strong disagreements between analytical models and indicated by recent experimental investigations. This reflects both the scarcity of accurate measurements and the difficulty of performing first-principle calculations of out-of-equilibrium processes in the WDM regime. We present the first ab-initio calculations of the e-i energy relaxation rates, a.k.a. couplings, in WDM. To this end, a Kubo relation for the e-i couplings was derived and methods were developed to compute them with quantum molecular dynamics. We discuss the results obtained for several materials (Al, H, Co, and Fe) across a wide range of WDM conditions, including the solid and liquid metal phases traversed in WDM experiments. Our approach serves as a comparison with measurements and model predictions, permits an extension into regimes not covered by experiments, and provides insight into the underlying physics.