Mile Viktória, Pusztai László, Dominguez Hector, Pizio Orest
Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary.
J Phys Chem B. 2009 Aug 6;113(31):10760-9. doi: 10.1021/jp900092g.
A detailed study of the microscopic structure of an electrolyte solution, cesium chloride (CsCl) in water, is presented. For revealing the influence of salt concentration on the structure, CsCl solutions at concentrations of 1.5, 7.5, and 15 mol % are investigated. For each concentration, we combine total scattering structure factors from neutron and X-ray diffraction and 10 partial radial distribution functions from molecular dynamics simulations in one single structural model, generated by reverse Monte Carlo modeling. This combination of computer modeling methods is capable of (a) showing the extent to which simulation results are consistent with experimental diffraction data and (b) tracking down distribution functions in computer simulation that are the least comfortable with diffraction data. For the present solutions, we show that the level of consistency between simulations that use simple pair potentials and experimental structure factors is nearly quantitative. Remaining inconsistencies seem to be caused by water-water distribution functions. Changing the pair potentials of water-water interactions from SPC/E to TIP4P-2005 has not had any effect in this respect. As a final result, we obtained particle configurations from reverse Monte Carlo modeling that were in quantitative agreement with both diffraction data and most of the molecular dynamics (MD) simulated partial radial distribution functions (prdf's). From the particle coordinates, the distribution of the number of first neighbors, as well as angular correlation functions, were calculated. The average number of water molecules around cations decreases from about 8 to about 6.5 as concentration increases from 1.5 to 15 mol %, whereas the same quantity for the anions changes from about 7 to about 5. It was also found that the average angle of Cl...H-O particle arrangements, characteristic of anion-water hydrogen bonds, is closer to 180 degrees than that found for O...H-O arrangements (water-water hydrogen bonds). The present combination of experimental and computer simulation methods appears to be promising for the study of other electrolyte solutions.
本文对电解质溶液——水中氯化铯（CsCl）的微观结构进行了详细研究。为揭示盐浓度对结构的影响，研究了浓度为1.5、7.5和15 mol%的CsCl溶液。对于每种浓度，我们将中子和X射线衍射的总散射结构因子与分子动力学模拟的10个部分径向分布函数结合在一个由反向蒙特卡罗建模生成的单一结构模型中。这种计算机建模方法的组合能够（a）显示模拟结果与实验衍射数据的一致程度，以及（b）追踪计算机模拟中与衍射数据最不相符的分布函数。对于当前的溶液，我们表明使用简单对势的模拟与实验结构因子之间的一致程度几乎是定量的。剩余的不一致似乎是由水-水分布函数引起的。在这方面，将水-水相互作用的对势从SPC/E更改为TIP4P-2005没有任何效果。作为最终结果，我们从反向蒙特卡罗建模中获得了与衍射数据以及大多数分子动力学（MD）模拟的部分径向分布函数（prdf）定量一致的粒子构型。根据粒子坐标，计算了第一近邻数的分布以及角关联函数。随着浓度从1.5 mol%增加到15 mol%，阳离子周围水分子的平均数量从约8个减少到约6.5个，而阴离子的相同数量则从约7个变为约5个。还发现，作为阴离子-水氢键特征的Cl...H-O粒子排列的平均角度比O...H-O排列（水-水氢键）的平均角度更接近180度。目前实验和计算机模拟方法的结合对于研究其他电解质溶液似乎很有前景。
