Influence of a Counterion on the Ion Atmosphere of an Anion: A Molecular Dynamics Study of LiX and CsX (X = F(-), Cl(-), I(-)) in Methanol.
Influence of a Counterion on the Ion Atmosphere of an Anion: A Molecular Dynamics Study of LiX and CsX (X = F(-), Cl(-), I(-)) in Methanol.
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DOI：
10.1021/acs.jpcb.5b00481
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发表时间：
2015-05
期刊：
影响因子：
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通讯作者：
Parveen Kumar;A. Kulkarni;S. Yashonath
中科院分区：
文献类型：
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作者：
Parveen Kumar;A. Kulkarni;S. Yashonath
我们报告了分子动力学（MD）模拟，以探讨在298 K下，在甲醇中的阳离子和阴离子溶剂化壳层的结构和动力学的一个counterparts的影响。我们表明，在离子对中的阳离子或阴离子的离子尺寸的变化影响的溶剂化结构的其他离子，以及在电解质溶液中的甲醇的扩散率。通过分析甲醇分子在第一溶剂化壳层（FSS）中的径向分布函数（RDFs）和取向，研究了不同离子尺寸的阳离子与其抗衡阴离子之间的离子缔合程度.结果表明，甲醇在FSS的阴离子以及阳离子表现出相当不同的径向和取向的结构相比，甲醇位于FSS的阴离子或阳离子，但不是两者。我们发现，F（-），Cl（-），和I（-）离子的配位数（CN）随着阴离子的尺寸的增加而减少，这与H2O中阴离子的趋势相反。用稳态图方法计算了甲醇分子在离子流固溶体中的平均停留时间。结果表明，离子-反离子相互作用对甲醇分子在离子FSS中的MRT有相当大的影响。我们还讨论了离子对的平均力势（PMFs）的离子计数器的稳定性顺序与不同大小的离子。PMF图显示Li（+）-F（-）对（小-小）在电解质溶液中是高度稳定的，而Li（+）-I（-）对是最不稳定的（小-大）。
We report molecular dynamics (MD) simulations to explore the influence of a counterion on the structure and dynamics of cationic and anionic solvation shells for various ions in methanol at 298 K. We show that the variation in ionic size of either the cation or the anion in an ion pair influences the solvation structure of the other ion as well as the diffusivity in an electrolyte solution of methanol. The extent of ionic association between the cation and its counteranion of different ionic sizes has been investigated by analyzing the radial distribution functions (RDFs) and the orientation of methanol molecules in the first solvation shell (FSS) of ions. It is shown that the methanol in the FSS of the anion as well the cation exhibit quite different radial and orientational structures as compared to methanol which lie in the FSS of either the anion or the cation but not both. We find that the coordination number (CN) of F(-), Cl(-), and I(-) ions decreases with increasing size of the anion which is contrary to the trend reported for the anions in H2O. The mean residence time (MRT) of methanol molecules in the FSS of ions has been calculated using the stable states picture (SSP) approach. It is seen that the ion-counterion interaction has a considerable influence on the MRT of methanol molecules in the FSS of ions. We also discuss the stability order of the ion-counterion using the potentials of mean force (PMFs) for ion pairs with ions of different sizes. The PMF plots reveal that the Li(+)-F(-) pair (small-small) is highly stable and the Li(+)-I(-) pair is least stable (small-large) in electrolyte solutions.