Pair potentials for warm dense matter and their application to x-ray Thomson scattering in aluminum and beryllium

We study the conductivities σ of (i) the equilibrium isochoric state (σis), (ii) the equilibrium isobaric state (σ ib ), and also the (iii) non-equilibrium ultrafast matter (UFM) state (σ uf ) with the ion temperature Ti less than the the electron temperature Te. Aluminum, lithium and carbon are considered, being increasingly complex warm dense matter (WDM) systems, with carbon having transient covalent bonds. First-principles calculations, i.e., neutral-pseudoatom (NPA) calculations and density-functional theory (DFT) with molecular-dynamics (MD) simulations, are compared where possible with experimental data to characterize σic, σ ib and σ uf . The NPA σ ib are closest to the available experimental data when compared to results from DFT+MD, where simulations of about 64-125 atoms are typically used. The published conductivities for Li are reviewed and the value at a temperature of 4.5 eV is examined using supporting X-ray Thomson scattering calculations. A physical picture of the variations of σ with temperature and density applicable to these materials is given. The insensitivity of σ to Te below 10 eV for carbon, compared to Al and Li, is clarified.

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“…[46]. The XRTS ion feature W (k) for Li at T = 4.5 eV and ρ = 0.6 g/cm 3 has been calculated (see Fig.…”

Section: Appendixmentioning

confidence: 99%

Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime

et al. 2017

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“…If Γ ei < 1, the ions still can a Te/T i was evaluated in Refs. [15,28] b Te/T i was evaluated in Ref. [28] c Te/T i was evaluated in Refs.…”

Section: Plasma Parametersmentioning

confidence: 99%

Structural characteristics of strongly coupled ions in a dense quantum plasma

et al. 2018

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The structural properties of strongly coupled ions in dense plasmas with moderately to strongly degenerate electrons are investigated in the framework of the one-component plasma model of ions interacting through a screened pair interaction potential. Special focus is put on the description of the electronic screening in the Singwi-Tosi-Land-Sjölander (STLS) approximation. Different cross-checks and analyses using ion potentials obtained from ground-state quantum Monte Carlo data, the random phase approximation (RPA), and existing analytical models are presented for the computation of the structural properties, such as the pair distribution and the static structure factor, of strongly coupled ions. The results are highly sensitive to the features of the screened pair interaction potential. This effect is particularly visible in the static structure factor. The applicability range of the screened potential computed from STLS is identified in terms of density and temperature of the electrons. It is demonstrated that at r_{s}>1, where r_{s} is the ratio of the mean interelectronic distance to the Bohr radius, electronic correlations beyond RPA have a nonnegligible effect on the structural properties. Additionally, the applicability of the hypernetted chain approximation for the calculation of the structural properties using the screened pair interaction potential is analyzed employing the effective coupling parameter approach.

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“…Since these simulations are computationally expensive, the use of a simpler approach such as the neutral pseudoatom (NPA) model is appropriate. The NPA is well adapted to extract the ion part of the XRTS signals [8] and will be the principal method used in this work, where we show that the NPA also has the needed accuracy. The XRTS spectrum can be computed in the NPA, and also by other means without using the Chihara decomposition [13,14] but its discussion is not needed for this work.…”

Section: Introductionmentioning

confidence: 97%

“…In the laboratory, WDM can be created through the interaction of high-energy short-pulse lasers with simple metals such as aluminum [4,5] and beryllium [6], with densities ρ several times the room density ρ 0 and temperatures of the order of 1 eV. The importance of treating these systems as two-temperature WDM systems rather than equilibrium systems has not always been appreciated in analyzing the experimental results [7,8].…”

Section: Introductionmentioning

confidence: 99%

Ion-ion dynamic structure factor, acoustic modes, and equation of state of two-temperature warm dense aluminum

et al. 2018

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The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasiequilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasiequilibrium situations. Analyzing the van Hove function, we find that ion-ion correlations vanish in a time significantly smaller than the electron-ion relaxation time so that dynamical properties have a physical meaning for the quasiequilibrium state. A significant increase in the speed of sound is predicted from the modification of the dispersion relation of the ion acoustic mode as the electron temperature is increased. The two-temperature equation of state including the free energy, internal energy, and pressure is also presented.

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Pair potentials for warm dense matter and their application to x-ray Thomson scattering in aluminum and beryllium

Cited by 20 publications

References 70 publications

Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime

Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime

Structural characteristics of strongly coupled ions in a dense quantum plasma

Ion-ion dynamic structure factor, acoustic modes, and equation of state of two-temperature warm dense aluminum

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