Dynamic Ion Structure Factor of Warm Dense Matter

Vorberger, Jan; Donkó, Zoltán; Ткаченко, И. М.; Gericke, Dirk O.

doi:10.1103/physrevlett.109.225001

Cited by 54 publications

(44 citation statements)

References 28 publications

(29 reference statements)

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“…Figure 5 compares the experimental pressure data with available empirical data 6 and state-of-the-art simulations. In particular, we show previous DFT-MD simulations for temperatures calculated for the shock Hugoniot 34 together with the DFT-MD simulations performed for the temperatures and densities in the present experiment 35 (the latter provide excellent agreement with the data). Our data further show no indication of Bragg peaks for compressed aluminium above P = 1.2 Mbar, consistent with previous melt line Experimental data (black curve) are fitted with theoretical dynamic structure factor calculations (red and blue curves).…”

Section: Discussionsupporting

confidence: 79%

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

et al. 2015

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In megabar shock waves, materials compress and undergo a phase transition to a dense charged-particle system that is dominated by strong correlations and quantum effects. This complex state, known as warm dense matter, exists in planetary interiors and many laboratory experiments (for example, during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions). Here, we apply record peak brightness X-rays at the Linac Coherent Light Source to resolve ionic interactions at atomic (ångström) scale lengths and to determine their physical properties. Our in situ measurements characterize the compressed lattice and resolve the transition to warm dense matter, demonstrating that short-range repulsion between ions must be accounted for to obtain accurate structure factor and equation of state data. In addition, the unique properties of the X-ray laser provide plasmon spectra that yield the temperature and density with unprecedented precision at micrometre-scale resolution in dynamic compression experiments. M aterials exposed to high pressures of 1 Mbar and above have recently been the subject of increased attention due to their importance for the physics of planetary formation 1-3 , for material science 4 and for inertial confinement fusion research 5 . The behaviour of shock-compressed aluminium is of particular interest because it has been proposed as a standard for shock-wave experiments 6 and is widely used for equation-of-state 7,8 and warm dense matter (WDM) 9,10 studies. At room temperature, aluminium has three delocalized electrons, so it provides a prototype for an ideal electron fluid. As temperatures and pressures increase, compressing and breaking ionic lattice bonds, strong ionic forces remain, resulting in significant deviations from a simple fluid.Simulations using density functional theory coupled to manyparticle molecular dynamics (DFT-MD) have evolved into an ab initio tool to explore this regime of high-pressure physics 11,12 . To date, these simulations have been used to predict physical properties derived from optical observations of particle and shock velocities. Studies of structural properties that are sensitive to many-particle electron-ion and ion-ion interaction physics 13 have been challenging 14 , although recent progress has been made using X-ray absorption spectroscopy 15,16 . Early experiments on fourth-generation light sources 17 have made use of X-ray diffraction and measured the structural evolution from elastic to plastic states 18 . However, pressures in the Mbar regime, as required for melting many solids, have only recently become available at the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS).Here we visualize, for the first time, the evolution of compressed matter across the melting line and the coexistence regime into a WDM state. The combination of high-power optical lasers and the X-ray beam at MEC provides high-resolution X-ray scattering at multi-Mbar pressures. Our data provide the io...

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Section: Discussionsupporting

confidence: 79%

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

et al. 2015

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“…Both free and bound electrons contribute to the elastic and the inelastic feature. Although screening is a very dynamic process, it can be considered in the ω = 0 limit for elastic scattering as the screening clouds q a are connected here to the ion structure with very slow modes [33]. However, screening needs to be considered dynamically for the inelastic free-electron term S 0 ee .…”

Section: Theory For the Electron Structure Factormentioning

confidence: 99%

Ab initioapproach to model x-ray diffraction in warm dense matter

Vorberger

Gericke

2015

Phys. Rev. E

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It is demonstrated how the static electron-electron structure factor in warm dense matter can be obtained from density functional theory in combination with quantum Monte Carlo data. In contrast to theories assuming well-separated bound and free states, this ab initio approach yields also valid results for systems close to the Mott transition (pressure ionization), where bound states are strongly modified and merge with the continuum. The approach is applied to x-ray Thomson scattering and compared to predictions of the Chihara formula whereby we use the ion-ion and electron-ion structure from the same simulations. The results show significant deviations of the screening cloud from the often applied Debye-like form.

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“…In the present work, we do not reconstruct the NPF from the very data we wish to describe like it was done in [22], but model it by its static value [9,10]: Qðq; ω; κÞ ¼ Qðq; 0; κÞ ¼ ihðq; κÞ, hðq; κÞ > 0. The latter positive parameter function was related in [10] to the static value of the DSF directly via (3).…”

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Direct Determination of Dynamic Properties of Coulomb and Yukawa Classical One-Component Plasmas

et al. 2017

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Dynamic characteristics of strongly coupled classical one-component Coulomb and Yukawa plasmas are obtained within the nonperturbative model-free moment approach without any data input from simulations so that the dynamic structure factor (DSF) satisfies the first three nonvanishing sum rules automatically. The DSF, dispersion, decay, sound speed, and other characteristics of the collective modes are determined using exclusively the static structure factor calculated from various theoretical approaches including the hypernetted chain approximation. A good quantitative agreement with molecular dynamics simulation data is achieved. . SCPs and warm dense matter are highly relevant model systems for inertial fusion devices [6]. The common property of SCPs is that the interparticle potential energy dominates over the thermal energy. Many of the above-mentioned systems have been analyzed and their characteristic effects became understood within the framework of a seminal model system, the one-component plasma (OCP) model that considers explicitly only one type of charged species, while the presence and the effects of other charged species are expressed by the interaction potential φðrÞ.SCPs, as many-body dynamical systems, exhibit various collective excitations, of which the properties have been investigated both via theoretical approaches and numerical simulations. Numerical approaches provide direct access to the central quantity of collective effects, the dynamic structure factor (DSF). The most successful theoretical approach capable of describing strongly coupled plasmas, the quasilocalized charge approximation [7], is able to predict [from the static pair distribution function (PDF)] the dispersion relations of the collective modes; however, it cannot predict the lifetime (decay) of the modes and the form of the DSF itself. Here we demonstrate that the method of moments theoretical approach [8] is able to predict the form and structure of the DSF of the OCP, based on static data only, i.e., the PDF or the static structure factor (SSF). As both the PDF and the SSF can be obtained theoretically as well [e.g., within the hypernetted chain (HNC) approximation and its modifications including the bridge function] the present approach provides a purely theoretical access to the full DSF and a full quantitative description of the collective modes, including their decay and other characteristics, without the necessity to use simulation data as input, as it was done in [9,10].The moment approach is nonperturbative, nonparametric, and model free. Thus it is perfectly applicable to a broad class of fluids characterized by response functions like semidegenerate multicomponent Coulomb systems or even simple liquids. Because of the rigorous mathematical background, the method is based on automatic satisfaction of sum rules and other exact relations. An empirical guidance is plugged directly into the intermediate step of theoretical computations, thus closing the approach and permitting us, in addition, to determine the dynamic...

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Dynamic Ion Structure Factor of Warm Dense Matter

Cited by 54 publications

References 28 publications

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

Ab initioapproach to model x-ray diffraction in warm dense matter

Direct Determination of Dynamic Properties of Coulomb and Yukawa Classical One-Component Plasmas

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