We present a model for electron-ion transport in Warm Dense Matter that incorporates Coulomb coupling effects into the quantum Boltzmann equation of Uehling and Uhlenbeck through the use of a statistical potential of mean force. Although this model has been derived rigorously in the classical limit [S.D. Baalrud and J. Daligault, Physics of Plasmas 26, 8, 082106 (2019)], its quantum generalization is complicated by the uncertainty principle. Here we apply an existing model for the potential of mean force based on the quantum Ornstein-Zernike equation coupled with an average-atom model [C. E. Starrett, High Energy Density Phys. 25, 8 (2017)]. This potential contains correlations due to both Coulomb coupling and exchange, and the collision kernel of the kinetic theory enforces Pauli blocking while allowing for electron diffraction and large-angle collisions. By solving the Uehling-Uhlenbeck equation for electron-ion relaxation rates, we predict the momentum and temperature relaxation time and electrical conductivity of solid density aluminum plasma based on electron-ion collisions. We present results for density and temperature conditions that span the transition from classical weakly-coupled plasma to degenerate moderately-coupled plasma. Our findings agree well with recent quantum molecular dynamics simulations.
We predict the emergence of novel collective electronic excitations in warm dense matter with an inhomogeneous electronic structure based on first-principles calculations. The emerging modes are controlled by the imposed perturbation amplitude. They include satellite signals around the standard plasmon feature, transformation of plasmons to optical modes, and double-plasmon modes. Most importantly, these modes exhibit a pronounced dependence on the temperature. This makes them potentially invaluable for the diagnostics of plasma parameters in the warm dense matter regime. We demonstrate that t…
The screening of a test charge by partially degenerate non-ideal free electrons at conditions related to warm dense matter and dense plasmas is investigated using linear response theory and the local field correction based on ab inito Quantum Monte-Carlo simulations data. The analysis of the obtained results is performed by comparing to the random phase approximation and the Singwi-Tosi-Land-Sjölander approximation. The applicability of the long-wavelength approximation for the description of screening is investigated. The impact of electronic exchange-correlations effects on structural proper…
Accurate modeling of the electronic structure of warm dense matter is a challenging problem whose solution would allow a better understanding of material properties like equation of state, opacity, and conductivity, with resulting applications from astrophysics to fusion energy research. Here we explore the real-space Green's function method as a technique for solving the Kohn-Sham density functional theory equations under warm dense matter conditions. We find the method to be tractable and accurate throughout the density and temperature range of interest, in contrast to other approaches. Good…
The rate of photon absorption in warm dense matter (WDM) induced by free-free electron-ion collisions is derived from Sommerfeld's cross-section for non-relativistic bremsstrahlung emission, making use of detailed balance relations. Warm dense matter is treated as a metal-like state in the approximation of a uniform degenerate electron gas and a uniform ion background. Total absorption rates are averaged over the electron Fermi distribution. A closed expression is obtained for the absorption rate, depending on temperature, density, and photon energy, that scales with ion charge Z. It is evalua…
The energy band structures caused by self-energy shifting that results in bound energy levels broadening and merging in warm dense aluminum and beryllium are observed. An energy band theory for warm dense matter (WDM) is proposed and a new code based on the energy band theory is developed to improve the traditional density functional method. Massive data of the equation of state and transport coefficients for WDM in medium and low Z have been simulated. The transition from fully degenerate to partially degenerate (related to WDM) and finally to non-degenerate state is investigated using the Lo…
We combine ab initio path integral Monte Carlo (PIMC) simulations with fixed ion configurations from density functional theory molecular dynamics (DFT-MD) simulations to solve the electronic problem for hydrogen under warm dense matter conditions [M.Böhme et. al. Phys.Rev.Lett.(in print)]. The problem of path collapse due to the Coulomb attraction is avoided by utilizing the pair approximation, which is compared against the simpler Kelbg pair-potential. We find very favourable convergence behaviour towards the former. Since we do not impose any nodal restrictions, our PIMC simulations are affl…
An effective potential approach in combination with the molecular dynamics (MD) method was used to study the effect of the ionic core on the transport properties of ions in the warm dense matter regime. As an example, we considered shocked silicon. The results of MD simulations within microcanonical ensemble were analyzed by computing the mean squared displacement (MSD) and the velocity autocorrelation function (VAF) of particles. The MSD and VAF are used to compute the diffusion coefficient of ions. The results are compared with the data computed neglecting the ion core effect. It is found th…
First-Principles Simulations of Warm Dense Lithium Fluoride
我们进行第一性原理路径积分蒙特卡罗（PIMC）和密度泛函理论分子动力学（DFT-MD）计算，以探索温暖的致密物质状态的LiF。我们的模拟覆盖了$2.08-15.70$ ~g、$\,$、cm、$^{-3}$和$10^4-10^9$ ~K的宽密度-温度范围。由于PIMC和DFT-MD精确地处理原子壳层结构的影响，我们发现一个明显的压缩最大值和一个肩膀上的主要Hugoniot曲线归因于K-壳层和L-壳层电离。结果为广泛使用的EOS表，如SEEOS，LEOS和模型提供了基准。此外，我们计算对关联函数，揭示了一个不断变化的等离子体结构和电离过程，驱动的热和压力电离。最后，我们计算电子态密度的液体LiF的DFT-MD模拟，并发现，电子间隙可以保持开放的密度和温度增加到至少15.7克$~$ cm $^{-3}$。
In a classical plasma the momentum distribution, $n(k)$, decays exponentially, for large $k$, and the same is observed for an ideal Fermi gas. However, when quantum and correlation effects are relevant simultaneously, an algebraic decay, $n_\infty(k)\sim k^{-8}$ has been predicted. This is of relevance for cross sections and threshold processes in dense plasmas that depend on the number of energetic particles. Here we present extensive \textit{ab initio} results for the momentum distribution of the nonideal uniform electron gas at warm dense matter conditions. Our results are based on first pr…
In the Ziman-Evans formulation, the electrical resistivity involves several quantities like the plasma mean ionization and chemical potential, the electron-ion scattering cross-section, the ion-ion structure factor, and the derivative of the Fermi distribution with respect to electron energy. Therefore, in order to make significant progress while comparing different models or analyzing experimental measurements, it is important to try to get insight into such partial physical quantities. In the present work, we propose to investigate the sensitivity of the resistivity to the different physical…
Warm dense matter is a highly active research area both at the frontier and interface of material science and plasma physics. We assess the performance of commonly used exchange-correlation (XC) approximation (LDA, PBE, PBEsol, and AM05) in the spin-polarized inhomogeneous electron gas under warm dense conditions based on exact path-integral quantum Monte-Carlo calculations. This extends our recent analysis on the relevance of inhomogeneities in the spin-unpolarized warm dense electron gas [Z.~Moldabekov et al., J. Chem. Phys. 155, 124116 (2021)]. We demonstrate that the predictive accuracy of…
Helmholtz-Zentrum Dresden Rossendorf（德累斯顿罗森多夫亥姆霍兹中心）；SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；GSI Helmholtzzentrum für Schwerionenforschung GmbH（GSI重离子研究中心亥姆霍兹有限公司）；School of Mathematics and Physics, Queen’s University of Belfast（贝尔法斯特女王大学数学与物理学院）；European XFEL（欧洲X射线自由电子激光设施）；Center for Computing Research, Sandia National Laboratories（桑迪亚国家实验室计算研究中心）；University of Exeter（埃克塞特大学）；Ecole Normale Supérieure de Lyon（里昂高等师范学校）；LULI, CNRS, CEA, Ecole Polytechnique—Institut Polytechnique de Paris（卢日-拉格朗日联合实验室，法国国家科学研究中心，法国原子能和替代能源委员会，巴黎综合理工学院—巴黎理工学院）；Department of Physics and Astronomy, University of Victoria（维多利亚大学物理与天文系）；Kiel Nano, Surface and Interface Science KiNSIS（基尔纳米、表面与界面科学KiNSIS）；Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel（基尔基督教阿尔伯特大学理论物理与天体物理研究所）
We present an approach to extend plasma transport theory into the Warm Dense Matter (WDM) regime characterized by moderate Coulomb coupling and electron degeneracy. It is based on a recently proposed closure of the BBGKY hierarchy that expands in terms of the departure of correlations from their equilibrium value, rather than in terms of the strength of correlations. This kinetic equation contains modifications to the collision term in addition to a second term that models the non-ideal contributions to the equation of state. An explicit collision operator is derived in the semiclassical limit…
Resonant Bound-Free Contributions to Thomson Scattering of X-rays by Warm Dense Matter
最近的计算[Nilsen et al. arXiv：1212.5972]预测，在金属密度和T=12 eV下，铬（Z=24）中3s和3 p束缚态对散射光子光谱的贡献低于相应的束缚态阈值。这些共振被证明是密切相关的连续降低，在自由原子中的3D束缚态溶解成共振l=2分波的连续。由此产生的d-态共振占主导地位的贡献的束缚-自由的动态结构功能，导致预测的共振散射X射线光谱。在周期表中Ca和Mn（20 <= Z <= 25）之间的所有元素中显示出类似的共振特征。
We investigate the energy loss characteristics of warm dense matter (WDM) and dense plasmas concentrating on the influence of electronic correlations. The basis for our analysis is a recently developed ab initio Quantum Monte-Carlo (QMC) based machine-learning representation of the static local field correction (LFC) [Dornheim et al., J. Chem. Phys. 151, 194104 (2019)], which provides an accurate description of the dynamical density response function of the electron gas at the considered parameters. We focus on the polarization-induced stopping power due to free electrons, the friction functio…
In a recent Letter [T.~Dornheim \emph{et al.}, Phys.~Rev.~Lett.~\textbf{125}, 085001 (2020)], we have presented the first \emph{ab initio} results for the nonlinear density response of electrons in the warm dense matter regime. In the present work, we extend these efforts by carrying out extensive new path integral Monte Carlo (PIMC) simulations of a \emph{ferromagnetic} electron gas that is subject to an external harmonic perturbation. This allows us to unambiguously quantify the impact of spin-effects on the nonlinear density response of the warm dense electron gas. In addition to their util…
Exploring and understanding ultrafast processes at the atomic level is a scientific challenge. Femtosecond X-ray Absorption Spectroscopy (XAS) is an essential experimental probing technic, as it can simultaneously reveal both electronic and atomic structures, and thus unravel their non-equilibrium dynamic interplay which is at the origin of most of the ultrafast mechanisms. However, despite considerable efforts, there is still no femtosecond X-ray source suitable for routine experiments. Here we show that betatron radiation from relativistic laser-plasma interaction combines ideal features for…
The study of warm dense matter, widely existing in nature and laboratories, is challenging due to the interplay of quantum and classical fluctuations. We develop a variational diagrammatic Monte Carlo method and determine the exchange-correlation kernel $K_{\rm XC}(q;T)$ of a warm dense electron gas for a broad range of temperature $T$ and momentum $q$. We observe several interesting physics, including the $T$-dependent evolution of the hump structure and the large-$q$ tail and the emergence of a scaling relation. Particularly, by deriving an analytical form for $q \to \infty$, we obtain large…
Ionization and temperature measurements in warm dense copper using x-ray absorption spectroscopy
Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Mechanical and Aerospace Engineering, University of California San Diego（加州大学圣地亚哥分校机械与航空航天工程系）；Laboratory for Laser Energetics, University of Rochester（罗切斯特大学激光能量学实验室）；Sandia National Laboratories（桑迪亚国家实验室）
