Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India.
J Chem Phys. 2010 Sep 21;133(11):114504. doi: 10.1063/1.3481656.
A molecular dynamics study of model ions in water is reported. The van der Waals diameter of both the cations and anions is varied. We have carried out two sets of simulations--with and without dispersion interaction--between the ion and water. Self-diffusivity of the ions exhibits an anomalous maximum as a function of the van der Waals diameter for both these sets. This existence of a maximum in self-diffusivity when there is no dispersion interaction between the ion and the water is attributed to the attractive term from electrostatic interactions. Detailed analysis of this effect shows that the solvent shell is more strongly defined in the presence of dispersion interactions. A smaller ion exhibits biexponential decay while a single exponential decay is seen for the ion with maximum diffusivity in the self-part of the intermediate scattering function. The solvent structure around the ion appears to determine much of the dynamics of the ion. Interesting trends are seen in the activation energies and these can be understood in terms of the levitation effect.
本文报道了模型离子在水中的分子动力学研究。改变了阳离子和阴离子的范德华直径。我们进行了两组模拟——离子与水之间存在和不存在色散相互作用。对于这两组模拟，离子的自扩散率都表现出随着范德华直径的异常最大值。当离子与水之间不存在色散相互作用时，自扩散率存在最大值，这归因于静电相互作用的吸引项。对这种效应的详细分析表明，在存在色散相互作用的情况下，溶剂壳更加明确。较小的离子表现出双指数衰减，而对于自部分中间散射函数中具有最大扩散率的离子，则观察到单指数衰减。离子周围的溶剂结构似乎决定了离子的大部分动力学。在活化能方面可以看到有趣的趋势，这些可以根据悬浮效应来理解。
