Electronic Density Response of Warm Dense Matter: From Simulations to Experiments

Matter at extreme densities and pressures is ubiquitous throughout our universe and naturally
occurs in astrophysical objects such as giant planet interiors. In addition, such warm dense
matter (WDM) is important for technological applications such as inertial confinement fusion
and the discovery of novel materials. Consequently, WDM is routinely studied in experiments
at large research facilities around the globe, including NIF, LCLS, Omega, and the Sandia Z-
machine in the USA, SACLA in Japan, and the European XFEL in Germany.
In practice, the extreme conditions render the accurate diagnostics of WDM a formidable
challenge as even basic parameters such as the temperature cannot be directly measured, and
have to be inferred indirectly from other observations. In this context, a particularly important
property is given by the electronic density response to an external perturbation, which is
probed for example in X-ray Thomson scattering (XRTS) experiments.
In this talk, I give an overview of a number of recent developments in this field [1].
Specifically, I show how we can use state-of-the-art computational methods such as quantum
Monte Carlo (QMC) [2,3] and density functional theory (DFT) simulations [4] to model a
gamut of electronic density response properties of WDM with unprecedented accuracy. In
addition, I present a new approach that allows one to diagnose the temperature of arbitrary
materials from XRTS experiments in the imaginary-time domain without any simulations or
approximations [5]. Finally, I outline a strategy for future developments based on the close
interplay between simulations and experiments.
Keywords: Warm-dense matter, Inelastic X-ray scattering, Path-integral Monte Carlo,
Density functional theory
References:
[1] T. Dornheim et al., Phys. Plasmas 30, 032705 (2023)
[2] T. Dornheim, J. Vorberger, and M. Bonitz, PRL 125, 085001 (2020)
[3] M. Böhme, Zh. Moldabekov, J. Vorberger, and T. Dornheim, PRL 129, 066402 (2022)
[4] Zh. Moldabekov et al., J. Chem. Theory. Comput. 19, 1286-1299 (2023)
[5] T. Dornheim et al., Nature Comm. 13, 7911 (2022)