温稠密硅及硅酸盐的X射线吸收特性的改进的第一性原理研究

Warm dense matter (WDM) has a typical density ranging from about solid density to several thousand times of solid density, and temperature varying from several thousand Kelvin to tens of million Kelvin. WDM exists widely in our universe, such as brown dwarfs, giant planets, and the core of the Earth. More importantly, the fuel of the inertial confinement fusion undergoes WDM region for quite a long period of time during implosion. Involving transition from inner shell electrons to unoccupied electronic states, X-ray absorption spectra (XAS) provide direct diagnose of electronic structures of WDM. Here we propose to investigate the electronic structure of WDM silicon and silicates by calculating their XAS using an improved first-principles method including two parts. First, finite-temperature exchange correlation functional is used instead of zero-temperature counterpart in XAS calculation. Second, hybrid functional method is used to tackle the many-body problem in WDM regime. Both will improve the accuracy of first-principles calculation for XAS. Silicon is a perfect example for semiconductors, and silicates are the major components of the mantle of the Earth. However, their XAS in WDM regime is seldom reported. Using silicon and silicates as illustrating examples, this project can help us better understand the physics of nonmetal-metal transition and ionization potential depression, etc., and provide theoretical foundation for experimental investigation of matter under extreme conditions.

温稠密物质广泛存在于褐矮星、行星和地球内核中，其密度范围从与固体密度相当到数千倍固体密度，温度在几千K至几千万K。惯性约束聚变的主燃料层在内爆压缩过程中也在相当长的时间内处在温稠密物质状态。X射线吸收谱涉及到内壳层电子到未占据态的跃迁过程，是诊断温稠密物质的重要手段，可以直接提供电子结构信息。本项目将对第一性原理方法进行改进，一方面考虑电子交换关联相互作用的有限温度效应，另一方面通过杂化泛函方法进行温稠密条件下的多体修正，更精确地对温稠密硅和硅酸盐的X射线吸收谱进行计算，并对它们的电子结构进行研究。单晶硅作为典型的半导体材料，硅酸盐作为地幔的主要组成部分，其温稠密状态下的X射线吸收谱极少被报道。以它们为例，本项目可以加深对金属化转变、电离势降低等物理过程的理解，为极端条件下物质结构的实验研究提供理论依据。

温/热稠密物质是介于凝聚态物质与理想等离子体之间的过渡物质状态，其密度范围通常在0.1倍固体密度到几千倍固体密度之间，温度范围通常在几千K至几千万K之间。本项目中，我们通过GW方法修正传统密度泛函理论，提升了对硅的能带结构的计算精度。我们在发展的ext-FPMD方法中分别采用两种新提出的有限温度交换关联泛函和传统的零温交换关联泛函，对温稠密硅进行了第一性原理计算，定量得到了有限温度效应对状态方程、雨贡纽曲线等的影响。通过机器学习方法建立了原子-电子一体化模拟工具DeepDOS，建立了电子态密度与局域原子环境的直接联系，为X射线吸收等实验提供理论支撑。采用量子力学精度的DeepMD方法对下地幔条件下的温稠密硅酸镁进行了研究，为地球物理和地球化学的研究提供了关键数据。