Static Electronic Density Response of Warm Dense Hydrogen: Ab initio Path Integral Monte Carlo Simulations

The properties of hydrogen under extreme conditions are important for many applications, including inertial confinement fusion and astrophysical models. A key quantity is given by the electronic density response to an external perturbation, which is probed in X-ray Thomson scattering (XRTS) experiments---the state of the art diagnostics from which system parameters like the free electron density n_e, the electronic temperature T_e, and the charge state Z can be inferred. In this work, we present highly accurate path integral Monte Carlo (PIMC) results for the static electronic density response of hydrogen. We obtain the static exchange--correlation (XC) kernel K_XC, which is of central relevance for many applications, such as time-dependent density functional theory (TD-DFT). This gives us a first unbiased look into the electronic density response of hydrogen in the warm-dense matter regime, thereby opening up a gamut of avenues for future research.