X-Ray Thomson scattering without the Chihara decomposition

TL;DR

This paper introduces a first-principles, Chihara-independent method using real-time finite-temperature TDDFT to calculate the dynamic structure factor of warm dense matter, providing clearer insights into electron behavior without traditional bound/free classifications.

Contribution

It applies real-time finite-temperature TDDFT to WDM, offering a new, unified approach to compute the dynamic structure factor without relying on the Chihara decomposition.

Findings

TDDFT results agree with Chihara-based calculations under experimental conditions

Provides a unified treatment of bound and free electrons in WDM

First application of real-time TDDFT to warm dense matter

Abstract

X-Ray Thomson Scattering (XRTS) is an important experimental technique used to measure the temperature, ionization state, structure, and density of warm dense matter (WDM). The fundamental property probed in these experiments is the electronic dynamic structure factor (DSF). In most models, this is decomposed into three terms [Chihara, J. Phys. F: Metal Phys. {\bf 17}, 295 (1987)] representing the response of tightly bound, loosely bound, and free electrons. Accompanying this decomposition is the classification of electrons as either bound or free, which is useful for gapped and cold systems but becomes increasingly questionable as temperatures and pressures increase into the WDM regime. In this work we provide unambiguous first principles calculations of the dynamic structure factor of warm dense beryllium, independent of the Chihara form, by treating bound and free states under a single formalism. The computational approach is real-time finite-temperature time-dependent density functional theory (TDDFT) being applied here for the first time to WDM. We compare results from TDDFT to Chihara-based calculations for experimentally relevant conditions in shock-compressed beryllium.