Tahara S, Kawakita Y, Shimakura H, Ohara K, Fukami T, Takeda S
Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan.
J-PARC Center, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1195, Japan.
J Chem Phys. 2015 Jul 28;143(4):044509. doi: 10.1063/1.4927507.
A first sharp diffraction peak (FSDP) is observed in the X-ray total structure factor of a molten mixture of RbCl-AgCl, while both pure melts of RbCl and AgCl do not exhibit FSDP individually. Molecular dynamics simulations were performed to investigate the origin of the FSDP with the polarizable ion model (PIM). Coexistence of covalent Ag-Cl and ionic Rb-Cl bonds leads the system to evolve intermediate range ordering, which is simulated by introducing the induced polarization in different ways between Ag-Cl with fully polarizable treatment based on Vashishta-Raman potential and Rb-Cl with suppression over-polarization in the nearest neighbor contribution based on Born-Meyer potential. The partial structure factors for both the Ag-Ag and Rb-Rb correlations, SAgAg(Q) and SRbRb(Q), show a positive contribution to the FSDP, while SAgRb(Q) for the Ag-Rb correlation exhibits a negative contribution, indicating that Ag and Rb ions are distributed in an alternating manner within the intermediate-range length scale. The origin of the intermediate-range chemical ordering of cations can be ascribed to the preferred direction of the dipole moments of anions in the PIM.
在RbCl - AgCl熔融混合物的X射线总结构因子中观察到一个第一尖锐衍射峰（FSDP），而RbCl和AgCl的纯熔体单独都不显示FSDP。进行了分子动力学模拟，以用可极化离子模型（PIM）研究FSDP的起源。共价Ag - Cl键和离子Rb - Cl键的共存导致系统发展出中间范围有序，这是通过基于Vashishta - Raman势对Ag - Cl进行完全可极化处理以及基于Born - Meyer势在最近邻贡献中抑制过极化对Rb - Cl以不同方式引入诱导极化来模拟的。Ag - Ag和Rb - Rb关联的部分结构因子SAgAg(Q)和SRbRb(Q)对FSDP有正贡献，而Ag - Rb关联的SAgRb(Q)显示负贡献，表明Ag和Rb离子在中间范围长度尺度内以交替方式分布。阳离子中间范围化学有序的起源可归因于PIM中阴离子偶极矩的优先方向。
