Unraveling the intrinsic atomic physics behind x-ray absorption line shifts in warm dense silicon plasmas
Unraveling the intrinsic atomic physics behind x-ray absorption line shifts in warm dense silicon plasmas
复制标题
揭示温暖致密硅等离子体中 X 射线吸收线移动背后的内在原子物理
DOI：
10.1103/physreve.103.033202
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发表时间：
2021
影响因子：
2.4
通讯作者：
Hu, S. X.
中科院分区：
文献类型：
--
作者：
Karasiev, Valentin V.;Hu, S. X.
我们提出了一种基于自由能密度泛函理论 (DFT) 的方法，用于计算热致密物质的光学性质，涵盖广泛的热力学条件和光子能量，包括整个 X 射线范围。它使用 Mermin-Kohn-Sham 密度泛函理论，并通过完全依赖于温度的广义梯度近似 XC 泛函考虑交换相关 (XC) 热效应。该方法将初始分子动力学 (AIMD) 快照 Kubo-Greenwood 光学数据与模拟单元计算中的单个原子相结合，以缩小边缘之间的光子能隙，并将边缘尾部延伸至多 keV 光子能量。由于使用 AIMD 快照进行 Kubo-Greenwood 计算所需的频带数量过多，因此标准方案中出现了这一差距。 Kubo-Greenwood 快照数据提供了对略超出边缘的低光子频率下的光学特性和近边缘 X 射线吸收结构 (XANES) 光谱的准确描述，而来自单原子周期性计算的数据覆盖了边缘以外的尾部区域。为了证明其对基于 DFT 的标准方法在计算上不可行的中间材料的适用性，我们将其应用于热致密硅等离子体的不透明度计算。这些第一原理计算揭示了沿着等温线和等容线的（）和边缘吸收的红移到蓝移的非常有趣的现象，这在传统等离子体物理的大多数连续降低模型中是不存在的。这种新的物理现象可以归因于由热致密等离子体条件引起的深层束缚核心电子的屏蔽和外壳电子的屏蔽之间的潜在竞争。我们进一步证明 X 射线吸收与边缘 X 射线吸收的比率可用于表征热致密等离子体条件。最终，根据我们的吸收计算，我们建立了硅在各种材料密度和温度下的第一原理不透光表（FPOT）。
We present a free-energy density functional theory (DFT)-based methodology for optical property calculations of warm dense matter to cover a wide range of thermodynamic conditions and photon energies including the entire x-ray range. It uses Mermin-Kohn-Sham density functional theory with exchange-correlation (XC) thermal effects taken into account via a fully temperature dependent generalized gradient approximation XC functional. The methodology incorporates a combination of theab initiomolecular dynamics (AIMD) snapshotted Kubo-Greenwood optic data with a single atom in simulation cell calculations to close the photon energy gap between theandedges and extend the-edge tail toward many-keV photon energies. This gap arises in the standard scheme due to a prohibitively large number of bands required for the Kubo-Greenwood calculations with AIMD snapshots. Kubo-Greenwood data on snapshots provide an accurate description of optic properties at low photon frequencies slightly beyond theedge and x-ray absorption near edges structure (XANES) spectra, while data from periodic calculations with single atoms cover the tail regions beyond the edges. To demonstrate its applicability to mid-materials where the standard DFT-based approach is not computationally feasible, we have applied it to opacity calculations of warm dense silicon plasmas. Thesefirst-principlescalculations revealed a very interesting phenomenon of redshift-to-blueshift in() and-edge absorptions along both isotherm and isochore, which are absent in most continuum-lowering models of traditional plasma physics. This new physics phenomenon can be attributed to the underlying competition between the screening of deeply bound core electrons and the screening of outer-shell electrons caused by warm-dense-plasma conditions. We further demonstrate that the ratio ofto the-edge x-ray absorptions can be used to characterize warm-dense-plasma conditions. Eventually, based on our absorption calculations, we have established afirst-principlesopacity table (FPOT) for silicon in a wide range of material densities and temperatures.