Dong Haitao, Liu Wenbin, Doren Douglas, Wood Robert
Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
J Phys Chem B. 2006 Sep 21;110(37):18504-14. doi: 10.1021/jp0628333.
The structure of an accurate ab initio model of aqueous chloride ion was calculated at two high-temperature state points (573 K, 0.725 g/cm(3) and 723 K, 0.0098 g/cm(3)) by a two-step procedure. First, the structure of an approximate model was calculated from a molecular dynamics simulation of the model. Then the difference between the structure of the ab initio model and the approximate model was calculated by non-Boltzmann weighting of a sample of configurations taken from the approximate model simulation. Radial distribution functions, average coordination numbers, the distribution of coordination numbers, an analysis of orientations of water in the first coordination shell, and the free energy of hydration of the chloride ion are reported for both state points. The most common water structure has one hydrogen close to the chloride ion and one pointing away (46% at 573 K and 57% at 723 K). Waters in the first coordination shell that are not strongly bound to the chloride ions are common. Several variations of the method were tested. Models in which the water-water interaction is calculated with ab initio methods predict only a slightly different structure than models in which water-water interactions are determined from the approximate models. Similarly, using the approximate model for solute-water interactions when the water is far from the chloride ion did not affect the results. Uncertainties due to the limited sample of configurations are estimated and found to be small. The results are in qualitative agreement with X-ray and neutron diffraction experiments and with simulations of approximate models.
通过两步程序，在两个高温状态点（573 K，0.725 g/cm³ 和 723 K，0.0098 g/cm³）计算了精确的氯化物离子水合从头算模型的结构。首先，从该模型的分子动力学模拟计算出近似模型的结构。然后通过对从近似模型模拟中获取的构型样本进行非玻尔兹曼加权，计算从头算模型与近似模型结构之间的差异。报告了两个状态点的径向分布函数、平均配位数、配位数分布、第一配位层中水分子取向分析以及氯离子的水合自由能。最常见的水结构是一个氢靠近氯离子，另一个背离氯离子（573 K 时为 46%，723 K 时为 57%）。第一配位层中未与氯离子紧密结合的水分子很常见。测试了该方法的几种变体。用从头算方法计算水 - 水相互作用的模型预测的结构与从近似模型确定水 - 水相互作用的模型相比，只有略微不同。同样，当水分子远离氯离子时，使用近似模型计算溶质 - 水相互作用不会影响结果。估计了由于构型样本有限导致的不确定性，发现其很小。结果与 X 射线和中子衍射实验以及近似模型的模拟在定性上一致。
