School of Physics, University of Sydney, New South Wales 2006, Australia.
J Chem Phys. 2010 Mar 21;132(11):114510. doi: 10.1063/1.3360310.
We perform ab initio molecular dynamics simulations to study the dissociation of NaCl in water. The potential of mean force (PMF) between the two ions is determined using the constrained-force method. The simulation windows corresponding to the contact and solvent-separated minima, and the transition state in between, are further analyzed to determine the changes in the properties of hydration waters such as coordination number, dipole moment, and orientation. The ab initio results are compared with those obtained from classical molecular dynamics simulations of aqueous NaCl using several common force fields. The ab initio PMF is found to have a shallower contact minimum and a smaller transition barrier compared with the classical ones. Also the binding free energy calculated from the ab initio PMF almost vanishes whereas it is negative for all the classical PMFs. Water dipole moments are observed to exhibit little change during dissociation, indicating that description of NaCl with a nonpolarizable force field may be feasible. However, overcoordination of the ion pair at all distances remains as a serious shortcoming of the current classical models. The ab initio results presented here provide useful guidance for alternative parametrizations of the nonpolarizable force fields as well as the polarizable ones currently under construction.
我们进行了从头分子动力学模拟，以研究 NaCl 在水中的解离。使用约束力法确定两个离子之间的平均力势（PMF）。进一步分析对应于接触和溶剂分离最小以及中间过渡态的模拟窗口，以确定水合水分子的性质（如配位数、偶极矩和取向）的变化。将从头算结果与使用几种常见力场的水溶液 NaCl 的经典分子动力学模拟结果进行比较。与经典的相比，从头算 PMF 具有更浅的接触最小和更小的过渡势垒。此外，从头算 PMF 计算的结合自由能几乎为零，而所有经典 PMF 的都是负值。在解离过程中观察到水分子偶极矩几乎没有变化，表明用非极化力场描述 NaCl 可能是可行的。然而，在所有距离处离子对的过度配位仍然是当前经典模型的严重缺点。这里呈现的从头算结果为非极化力场以及当前正在构建的极化力场的替代参数化提供了有用的指导。
