热稠密物质体系中复杂流体的理论及其对液态碳中不寻常的相变的应用
Theory of complex fluids in the warm-dense-matter regime, and application to an unusual phase-transitions in liquid carbon
摘要：
将最近的激光冲击实验、分子动力学（MD）的密度泛函理论（DFT）和碳的路径积分蒙特卡罗（PIMC）模拟的数据与碳的中性伪原子（NPA）+超网链（HNC）方法的预测进行比较，碳是暖密物质体系中的复杂液体。NPA的结果是在良好的协议，不仅与高密度制度，已通过PIMC的研究，但即使在低密度和低温下，瞬时共价键占主导地位的离子相关性。因此，由于在$\sim$ 1.4-1.6 eV $\,$处的C-C键的“预峰”和在来自DFT+MD模拟的在0.86 eV和3.7 g/cm $^3$等处的对分布函数中发现的其它特征，在NPA+HNC计算中准确恢复。这样的C-C键合峰还没有被捕获通过平均原子离子层（IS）模型。一个不寻常的液体$\to$蒸汽和金属$\to$半金属过渡同时发生的证据。这里，具有瞬时C-C键的强相关金属液体，即，密度$\sim$ 1.0 g/cm 2 $^3$和平均电离$Z=4$的碳突然转变为7 eV的无序单原子蒸气，其中$Z\simeq$ 3。还注意到$Z$突然下降的其他病例。$Z$的性质，它的不连续性，交换相关的作用，进行了审查。讨论了IS模型在描述热致密物质中瞬时共价键物理过程中的局限性。
英文摘要：
Data from recent laser-shock experiments, density-functional theory (DFT) with molecular-dynamics (MD), and path-integral Monte Carlo (PIMC) simulations on carbon are compared with predictions from the neutral-pseudo-atom (NPA)+ hyper-netted-chain (HNC) approach for carbon, a complex liquid in the warm-dense matter regime. The NPA results are in good agreement, not only with high-density regimes that have been studies via PIMC, but even at low densities and low temperatures where transient covalent bonding dominates ionic correlations. Thus the `pre-peak' due to the C-C bond at $\sim$1.4-1.6 Å$\,$ and other features found in the pair-distribution function from DFT+MD simulations at 0.86 eV and 3.7 g/cm$^3$ etc., are recovered accurately in the NPA+HNC calculations. Such C-C bonding peaks have not been captured via average-atom ion-sphere (IS) models. Evidence for an unusual liquid $\to$ vapor and metal$\to$ semi-metal transition occurring simultaneously is presented. Here a strongly correlated metallic-liquid with transient C-C bonds, i.e., carbon at density $\sim$ 1.0 g/cm$^3$ and mean ionization $Z=4$ transits abruptly to a disordered mono-atomic vapour at 7 eV, with $Z\simeq$ 3. Other cases where $Z$ drops abruptly are also noted. The nature of $Z$, its discontinuities, and the role of exchange correlation, are reviewed. The limitations of IS models in capturing the physics of transient covalent bonding in warm dense matter are discussed.
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