Ab initio Molecular-Dynamics Study of Dynamic and Electronic Properties of Molten Noble-Metal Halides

我们采用从头算分子动力学模拟方法研究了熔融贵金属卤化物的动力学和电子性质.通过对熔融态CuI的计算，证实了尽管同种离子间存在相关性，但Cu-Cu对的最近邻距离与Cu-I对的最近邻距离几乎相同。结果表明，Cu离子的原子分浓度存在较大的波动，以保持Cu-Cu间的短距离，而碘离子分布均匀。布居分析表明，相邻Cu离子之间以及Cu和I离子之间存在类共价键. Ag-Ag对在AgI熔体中的对分布函数表明，在Ag-Fe周围存在一个弱而清晰的Ag配位壳层，其平均原子间距与Ag-I对的平均原子间距相近。由于最近邻Ag-Ag距离如此短，Ag离子的密度分布在几埃的中间长度尺度上波动，这在约1埃的波矢处给出结构因子的峰<-1>。布居分析表明，银离子之间存在相互作用，这是由于银离子上的电荷分布引起的.相应于最近的X射线散射实验，我们研究了压力对熔融碘化银的结构和电子性质的依赖性。它已被证明，非常短的银-银相关保留高达20 GPa。通过对Ag_2Se超离子相的模拟，证实了Ag离子具有与贵金属卤化物相同的反常关联。通过研究银离子之间的位移相关函数，它已被澄清，银离子表现出集体运动时，他们与相邻的银离子迁移相邻的四面体网站之间。

We have investigated the dynamic and electronic properties of molten noble-metal halides by ab initio molecular-dynamics simulations.1. From the Calculations for molten CuI, we have confirmed that the nearest-neighbor distance for Cu-Cu pair is almost the same as that for Cu-I pair in spite of the correlation between the same type of ions. It has been shown that there exists a large fluctuation in the partial atomic concentration of Cu ions to retain the anomalously short Cu-Cu distance, while iodine ions distribute uniformly. It has been clarified by the population analysis that there is a covalent-like bonding between neighboring Cu ions as well as between Cu and I ions.2. The pair distribution function for Ag-Ag pairs in molten AgI shows that there is a weak but clear Ag coordination shell around Ag iron s with an average interatomic distance, which is close to that for Ag-I pairs. As a result of such a short nearest-neighbor Ag-Ag distance, the density distribution of Ag ions fluctuates on an intermediate length scale of a few angstroms, which gives a hump in the structure factor at a wave vector of about 1 Å^<-1>. From population analysis, it has been revealed that there exists an interaction between Ag ions due to the electronic charges that spread over ions.3. Corresponding to the recent X-ray scattering experiments, we have investigated the pressure dependence of the structural and electronic properties of molten AgI. It has been shown that the anomalously short Ag-Ag correlation is retained up to 20 GPa.4. From the simulations for the superionic phase of Ag2Se, we have confirmed that Ag ions have the anomalous correlation as in noble-metal halides. By investigating the displacement-correlation functions between Ag ions, it has been clarified that Ag ions exhibit a collective motion with their neighbor Ag ions when they migrate between neighboring tetrahedral sites.