Medical Scientist Training Program, Washington University in St. Louis, St. Louis, Missouri 63130-4899, USA.
J Chem Phys. 2012 Aug 14;137(6):064104. doi: 10.1063/1.4742068.
Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-derived parameters for the primitive model and the Lennard-Jones model with Lorentz-Berthelot mixing rules. The resulting parameters successfully reproduce the lattice properties used to derive them and are free from the influence of any water model. To assess the transferability of the Lennard-Jones parameters to aqueous systems, we used them to estimate hydration free energies and found that the results were in quantitative agreement with experimentally measured values. These lattice-derived parameters are applicable in simulations where coupling of ion parameters to a particular solvent model is undesirable. The simplicity and low computational demands of the calibration procedure make it suitable for parametrization of crystallizable ions in a variety of force fields.
准确的碱金属和卤化物离子在水溶液中的模型对于广泛的系统的计算机模拟是必要的。以前开发离子力场的努力通常集中在再现水合自由能和离子-水分布函数等水溶液性质的实验测量上。这种依赖性限制了所得参数的可转移性，因为水模型的多样性和已知的局限性。我们提出了一种基于晶体晶格性质的溶剂独立的离子参数校准方法。我们的程序依赖于晶格和的最小化来计算晶格能和离子间距离，而不是密集流体的平衡系综模拟。计算效率的提高使我们能够同时优化所有参数，包括 Li+、Na+、K+、Rb+、Cs+、F-、Cl-、Br-和 I-，同时受约束以确保与元素周期表趋势一致。我们通过展示原始模型和具有 Lorentz-Berthelot 混合规则的 Lennard-Jones 模型的晶格衍生参数来演示该方法。所得参数成功地再现了用于导出它们的晶格性质，并且不受任何水模型的影响。为了评估 Lennard-Jones 参数对水相系统的可转移性，我们使用它们来估计水合自由能，发现结果与实验测量值定量一致。这些晶格衍生参数可用于模拟中，其中不希望将离子参数耦合到特定的溶剂模型。校准过程的简单性和低计算需求使其适用于各种力场中可结晶离子的参数化。
