Abstract
Warm dense matter (WDM)—an exotic state of highly compressed matter—has attracted increased interest in recent years in astrophysics and for dense laboratory systems. At the same time, this state is extremely difficult to treat theoretically. This is due to the simultaneous appearance of quantum degeneracy, Coulomb correlations, and thermal effects, as well as the overlap of plasma and condensed phases. Recent breakthroughs are due to the successful application of density functional theory (DFT) methods which, however, often lack the necessary accuracy and predictive capability for WDM applications. The situation has changed with the availability of the first ab initio data for the exchange–correlation free energy of the warm dense uniform electron gas (UEG) that were obtained by quantum Monte Carlo (QMC) simulations; for recent reviews, see Dornheim et al., Phys. Plasmas 24, 056303 (2017) and Phys. Rep. 744, 1–86 (2018). In the present article, we review recent further progress in QMC simulations of the warm dense UEG: namely, ab initio results for the static local field correction G(q) and for the dynamic structure factor S(q,ω). These data are of key relevance for comparison with x-ray scattering experiments at free electron laser facilities and for the improvement of theoretical models. In the second part of this paper, we discuss the simulations of WDM out of equilibrium. The theoretical approaches include Born-Oppenheimer molecular dynamics, quantum kinetic theory, time-dependent DFT, and hydrodynamics. Here, we analyze the strengths and limitations of these methods and argue that progress in WDM simulations will require a suitable combination of all methods. A particular role might be played by quantum hydrodynamics, and we concentrate on problems, recent progress, and possible improvements of this method.
Highlights
Warm dense matter (WDM) has become a mature research field on the boarder of plasma physics and condensed matter physics, e.g., Refs. 1–4
In the remainder of this section, we discuss the quantum hydrodynamics approach and its relation to DFT89 more in detail because the former is comparatively less discussed for WDM applications, even though it appears to be filling a gap in the arsenal of simulation techniques, what we discuss in Sec
We have presented the thermodynamic results for the degenerate electron component, considering the warm dense uniform electron gas, that are based on ab initio quantum Monte Carlo simulations
Summary
Warm dense matter (WDM) has become a mature research field on the boarder of plasma physics and condensed matter physics, e.g., Refs. 1–4. Warm dense matter (WDM) has become a mature research field on the boarder of plasma physics and condensed matter physics, e.g., Refs. There are many examples in astrophysics such as the plasma-like matter in brown and white dwarf stars,[5,6,7] giant planets, e.g., Refs. 8–13, and the outer crust of neutron stars.[14,15] Warm dense matter is thought to exist in the interior of Earth.[16] In the laboratory, WDM is being routinely produced via laser or ion beam compression or with Z-pinches, see Ref. 17 for a recent review article.
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