Abstract
X-ray Thomson scattering 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. In most models, this is decomposed into three terms [J. Chihara, J. Phys. F 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.
Highlights
Warm dense matter (WDM) arises in many contexts ranging from planetary science [1,2,3] to the implosion stage of inertial confinement fusion [4,5,6]
While there are no sharp pressure, temperature, and density boundaries for the WDM regime, it is generally viewed as an intermediate state between a condensed phase and an ideal plasma where Fermi degeneracy is present, and the Coulomb coupling and thermal energy are comparable in magnitude [7]
We transcend the Chihara decomposition by explicitly simulating the real-time dynamics of warm dense matter using a finite temperature form of time-dependent density functional theory (TDDFT) [21,22] and the Published by the American Physical Society week ending 18 MARCH 2016 projector augmented-wave (PAW) formalism [23,24]
Summary
Warm dense matter (WDM) arises in many contexts ranging from planetary science [1,2,3] to the implosion stage of inertial confinement fusion [4,5,6]. We transcend the Chihara decomposition by explicitly simulating the real-time dynamics of warm dense matter using a finite temperature form of time-dependent density functional theory (TDDFT) [21,22] and the Published by the American Physical Society week ending 18 MARCH 2016 projector augmented-wave (PAW) formalism [23,24]. Our results come from averaging the response of electronic densities generated from several static uncorrelated ionic configurations sampled from thermally equilibrated DFT-MD calculations.
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