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中国物理学会期刊

基于单原子近似的等离子体屏蔽模型及其在原子结构计算中的应用

Plasma Screening Models Based on the Single-Atom Approximation and Their Applications in Atomic Structure Calculations

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  • 等离子体环境对嵌入其中的原子结构和原子参数具有显著影响,准确描述等离子体屏蔽效应是理解天体物理和实验室高能量密度物理中物质状态与演化规律的关键。基于单原子近似的等离子体屏蔽模型因其物理图像清晰、计算量可控,在等离子体诊断与模拟中被广泛应用。本文系统梳理了基于单原子近似的等离子体屏蔽模型及其在原子结构计算中的应用,以简并参数Θ和耦合参数Γee为基本分类框架,沿两条理论脉络展开综述。第一条脉络以Thomas-Fermi(TF)模型为起点,涵盖从经典Debye-Hückel(DH)模型到考虑统计涨落的非广延修正DH模型、计入量子衍射效应的余弦屏蔽模型,以及基于无轨道密度泛函理论引入梯度修正和交换—关联效应的梯度修正屏蔽模型,展现了从理想等离子体向温稠密等离子体的理论拓展路径。第二条脉络以离子球模型为起点,从均匀电子密度离子球模型出发,到自洽求解电子密度空间分布的自洽离子球模型、解析离子球模型、两步Hartree-Fock-Slater模型,以及纳入价带束缚-自由连续结构屏蔽模型,体现了对强耦合等离子体中电子非均匀性和能带形成描述的逐步精细化。在此基础上,本文介绍了本课题组发展的两类模型及其在原子结构计算中的应用:(1)分区DH模型,通过空间分区策略修正标准DH模型的近程缺陷,并在类H至类C等多种等电子序列离子中建立跃迁能线移和振子强度随等离子体屏蔽强度变化的标度规律;(2)原子态相关等离子体屏蔽模型,通过引入能带电子贡献和非弹性散射过程对电子分布的影响,为从弱耦合到强耦合、从非简并到强简并的宽广等离子体参数区间提供统一的屏蔽理论框架。本文的工作旨在为读者提供一条理解基于单原子近似的等离子体屏蔽模型发展全貌的清晰线索,揭示各模型之间的内在联系与演化脉络,展示当前不同模型在原子结构及参数计算方面的应用情况,为等离子体原子结构计算中屏蔽模型的合理选择提供参考。

     

    The plasma environment significantly affects the atomic structures and parameters of embedded atoms, and accurately describing plasma screening effects is essential for understanding the state and evolution of matter in astrophysical objects and laboratory high-energy-density physics facilities. Owing to their intuitive physical interpretations and moderate computational cost, plasma screening models based on the single-atom approximation are widely employed in plasma diagnostic analysis and numerical simulations. This review systematically surveys the full spectrum of single-atom-based plasma screening models and their implementations in atomic structure computations. The degeneracy parameter Θ and the coupling parameter Γee are adopted as a unified classification benchmark. The review is organized along two distinct developmental chains based on these parameters. The first chain originates from the Thomas-Fermi (TF) formalism, encompassing the classical Debye-Hückel (DH) model, the non-extensive modified DH model that accounts for statistical fluctuations, the cosine-screened Coulomb potential, which incorporates quantum diffraction effects, and the gradient-corrected screening model that includes gradient corrections and exchange-correlation effects within the framework of orbital-free density functional theory. This chain traces the theoretical improvements extending from ideal or weakly coupled plasmas to warm dense matter regimes. The second chain starts from the ion-sphere ansatz, evolving from the uniform-electron-density ion-sphere model, self-consistent ion-sphere models that determines the spatial distribution of the electron density self-consistently, the analytical ion-sphere model, to the two-step Hartree-Fock-Slater model, and the valence-band bound-free-continuum screening model. This chain demonstrates progressive refinements in describing electron non-uniformity and band formation in strongly coupled plasmas. On this theoretical basis, we elaborate two models developed by our group alongside their applications in atomic structure calculations. (1) the partitioned DH model, which corrects the short-range deficiency of the standard DH model through a spatial partitioning strategy. Scaling laws are established for transition-energy shifts and oscillator strengths as functions of the plasma screening intensity across multiple isoelectronic sequences ranging from H-like to C-like ions. (2) the atomic-state-dependent plasma screening model, which incorporates the contribution of band electrons and the influence of inelastic scattering processes on the electron distribution. This model provides a unified screening framework that can be applied in a wide range of plasma parameters, ranging from weakly to strongly coupled regimes and from non-degenerate to strongly degenerate conditions. This review intends to provide the reader a coherent and holistic overview of single-atom-approximation-based plasma screening models. We want to elucidate the intrinsic connections and evolutionary relationships among different models, and present their current applications in atomic structure and parameter calculations. We hope this review can deliver practical guidance for selecting appropriate screening models in plasma atomic structure computations.

     

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