Departamento de Química-Física I (Unidad de I+D+i Asociada al CSIC), Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Instituto de Química Física Rocasolano, CSIC, C/ Serrano 119, 28006 Madrid, Spain.
J Chem Phys. 2022 Apr 7;156(13):134503. doi: 10.1063/5.0085051.
Salt aqueous solutions are relevant in many fields, ranging from biological systems to seawater. Thus, the availability of a force-field that is able to reproduce the thermodynamic and dynamic behavior of salt aqueous solutions would be of great interest. Unfortunately, this has been proven challenging, and most of the existing force-fields fail to reproduce much of their behavior. In particular, the diffusion of water or the salt solubility are often not well reproduced by most of the existing force-fields. Recently, the Madrid-2019 model was proposed, and it was shown that this force-field, which uses the TIP4P/2005 model for water and non-integer charges for the ions, provides a good description of a large number of properties, including the solution densities, viscosities, and the diffusion of water. In this work, we assess the performance of this force-field on the evaluation of the freezing point depression. Although the freezing point depression is a colligative property that at low salt concentrations depends solely on properties of pure water, a good model for the electrolytes is needed to accurately predict the freezing point depression at moderate and high salt concentrations. The coexistence line between ice and several salt aqueous solutions (NaCl, KCl, LiCl, MgCl, and LiSO) up to the eutectic point is estimated from direct coexistence molecular dynamics simulations. Our results show that this force-field reproduces fairly well the experimentally measured freezing point depression with respect to pure water freezing for all the salts and at all the compositions considered.
盐水溶液在许多领域都有应用，包括生物系统和海水。因此，能够再现盐水溶液热力学和动力学行为的力场将是非常有意义的。不幸的是，这已经被证明是具有挑战性的，并且大多数现有的力场都无法再现它们的大部分行为。特别是，大多数现有的力场往往无法很好地再现水的扩散或盐的溶解度。最近，提出了马德里-2019 模型，该模型表明，这种力场使用 TIP4P/2005 模型来模拟水，并用非整数电荷来模拟离子，可以很好地描述大量性质，包括溶液密度、粘度和水的扩散。在这项工作中，我们评估了该力场在评估冰点降低方面的性能。尽管冰点降低是一种依数性质，在低盐浓度下仅取决于纯水的性质，但需要一个好的电解质模型来准确预测中高盐浓度下的冰点降低。通过直接共存分子动力学模拟来估计冰和几种盐水溶液（NaCl、KCl、LiCl、MgCl 和 LiSO）之间的共存线，直到共晶点。我们的结果表明，该力场能够很好地再现所有盐和所有考虑的组成相对于纯水冻结的实验测量的冰点降低。
