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

我们用从头算分子动力学模拟方法研究了贵金属卤化物熔体的动力学和电子性质。通过对熔融CuI的计算，我们证实了尽管同类型离子之间存在关联，但铜-铜对的近邻距离与铜-I对的近邻距离几乎相同。结果表明，为了保持反常的短的铜-铜距离，铜离子的部分原子浓度存在较大的波动，而碘离子的分布是均匀的。布居分析表明，相邻的铜离子之间以及铜和碘离子之间存在类共价键。Ag-Ag对在熔融AgI中的分布函数表明，在AgFe S周围有一个较弱但清晰的Ag配位壳，平均原子间距与Ag-I配位壳相近。由于如此短的近邻Ag-Ag距离，Ag离子的密度分布在几埃的中等长度尺度上波动，这使得结构因子在大约1Å^&lt；-1&gt；的波矢处有一个驼峰。布居分析表明，银离子之间存在着相互作用，这是由于扩散在离子上的电荷所致。与最近的X射线散射实验相对应，我们研究了熔融AgI的结构和电子性质与压力的关系。结果表明，反常短的银-银关联可保持到20GPa.4。从对Ag2Se上离子相的模拟中，我们证实了银离子和贵金属卤化物一样具有反常关联。通过对银离子间位移关联函数的研究，阐明了当银离子在相邻的四面体位置之间迁移时，它们与其相邻的银离子呈现集体运动。

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.