AgI分子极化效应的分子动力学研究
Molecular Dynamics Study of Polarization Effects on AgI
摘要：
用分子动力学模拟研究了AgI的三种不同模型。第一个是刚性离子模型（RIM），有效对势的Vashishta和Rahman的形式和参数化的Shimojo和Kobayashi提出的。另外两个是可极化离子模型，其中诱导极化效应已被添加到RIM有效对电位。在其中之一（PIM 1），只有阴离子被假定为可极化的局部电场。在另一个（PIM 2）的银极化也包括在内，和一个短程重叠的诱导极化相反的电诱导偶极矩。这种短程极化被证明是必要的，以避免overpolarization时，这两个物种被假定为极化。这三个模型再现了573 K下α-碘化银的超离子特性和923 K下熔融碘化银的液态行为。对于PIM 1获得的α-相中的阳离子的平均空间分布似乎与实验数据分析更好地一致。PIM 1还再现了结构因子prepeak在约1埃观察到从熔融碘化银的中子衍射数据的倒数。这三种模型保留在液相中的超离子字符的α-碘化银作为阳离子的流动性是显着大于阴离子。极化离子模型的离子电导率与实验数据的α-碘化银和熔融碘化银是更好的协议。
英文摘要：
Three different models of AgI are studied by molecular dynamics simulations. The first one is the rigid ion model (RIM) with the effective pair potential of the Vashishta and Rahman form and the parameterization proposed by Shimojo and Kobayashi. The other two are polarizable ion models in which the induced polarization effects have been added to the RIM effective pair potential. In one of them (PIM1) only the anions are assumed to be polarizable by the local electric field. In the other one (PIM2s) the silver polarization is also included, and a short-range overlap induced polarization opposes the electrically induced dipole moments. This short-range polarization is proved to be necessary to avoid overpolarization when both species are assumed to be polarizable. The three models reproduce the superionic character of alpha-AgI at 573 K and the liquid behavior of molten AgI at 923 K. The averaged spatial distribution of the cations in the alpha-phase obtained for PIM1 appears to be in better agreement with experimental data analysis. The PIM1 also reproduces the structure factor prepeak at about 1 reciprocal angstrom observed from neutron diffraction data of molten AgI. The three models retain in the liquid phase the superionic character of alpha-AgI as the mobility of the cations is significantly larger than that for the anions. The ionic conductivity for the polarizable ion models is in better agreement with experimental data for alpha-AgI and molten AgI.
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