The effects of ion and electric field on the vapor–liquid transition of water, are studied by using the optimal point charge (OPC) water model in this paper. A canonical Molecular Dynamics (MD) simulation approach, which calculates equilibrium time and the number of water molecules in the clusters, is employed to study the factors affecting the nucleation of water molecules. In addition, Quantum Mechanics (QM) method is adopted to calculate the hydration free energy of ions as a supplement. The results demonstrate that the ion has a significant promoting effect on vapor–liquid nucleation below the critical nucleus size (1–3 nm). However, as the cluster grows, the ion will no longer promote cluster growth, due to electrostatic shielding effect from the aggregated water molecules. When a weak uniform electric field (less than 0.1 V/nm) is applied, the promotion of the ion reappears. According to the trajectory analysis of ion in the water droplet, we believe that the electric field changes the relative position of ions in the droplets, thus weakening the shielding of water molecules. It is further demonstrated by a proposed novel statistical method, which provides an alternative, visualized and effective approach to evaluate the promotion effect in similar analyses, compared to radial distribution function.

本文利用最优点电荷（OPC）水模型研究了离子和电场对水汽-液相转变的影响。采用经典的分子动力学（MD）模拟方法计算平衡时间和簇中水分子的数量，以研究影响水分子成核的因素。另外，采用量子力学（QM）方法来计算离子的水合自由能。结果表明，在临界核尺寸（1-3 nm）以下，离子对气液成核具有显着的促进作用。但是，随着团簇的生长，由于聚集的水分子的静电屏蔽作用，离子将不再促进团簇的生长。当施加弱的均匀电场（小于0.1 V / nm）时，离子的促进再次出现。根据水滴中离子的轨迹分析，我们认为电场会改变水滴中离子的相对位置，从而削弱对水分子的屏蔽。提议的新型统计方法进一步证明了这一点，与径向分布函数相比，该方法提供了另一种可视化有效的方法来评估类似分析中的促进效果。