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研究了熔融贵金属卤化物的动力学和电子性质。从熔融态CuI的计算中，我们已经证实，尽管相同类型的离子之间存在相关性，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离子的部分原子浓度存在较大的波动，以保持Cu-Cu之间异常短的距离，而碘离子分布均匀。种群分析表明，相邻Cu离子之间以及Cu与I离子之间存在类似共价键的结合。熔态AgI中Ag-Ag对的对分布函数表明，Ag-铁s周围存在一个弱但清晰的Ag配位壳层，其平均原子间距离与Ag- i对接近。由于如此短的最近邻Ag-Ag距离，Ag离子的密度分布在几埃的中间长度尺度上波动，这使得结构因子在波矢量约为1 Å^<-1>处出现了一个峰。从总体分析可以看出，由于电荷分布在离子上，离子之间存在着相互作用。与最近的x射线散射实验相对应，我们研究了熔融AgI结构和电子特性的压力依赖性。结果表明，异常短的Ag-Ag相关性在20gpa以下仍然存在。通过对Ag2Se超离子相的模拟，我们证实了Ag离子与贵金属卤化物的异常相关性。通过研究银离子之间的位移相关函数，明确了银离子在邻近四面体位点之间迁移时与其相邻的银离子表现出集体运动。

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.