Temperature and structural changes of water clusters in vacuum due to evaporation
Temperature and structural changes of water clusters in vacuum due to evaporation
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DOI：
10.1063/1.2357591
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发表时间：
2006-10-21
影响因子：
4.4
通讯作者：
van der Spoel, David
中科院分区：
文献类型：
--
作者：
Caleman, Carl;van der Spoel, David
本文对纯水团簇的蒸发进行了研究。分子动力学模拟之间的20 ns和3亩的集群范围从125到4096分子在真空中进行。三种不同的模型（SPC，TIP4P和TIP5P）用于模拟水，从250，275和300 K的温度开始。我们监测的温度，氢键的数量，四面体的顺序，蒸发，径向分布函数，和扩散系数。就温度和蒸发而言，这三个模型的表现非常相似。在较高温度下开始的团簇显示出较高的初始蒸发速率，因此更快地达到蒸发停止的点（约240 K）。在0.5 μ s后，团簇的半径减小0.16 - 0.22 nm（较大的团簇倾向于稍微更多地减小其半径），这对应于大约每nm蒸发一个分子（2）。当从275 K开始时，团簇温度似乎向215 K收敛，与团簇大小无关。我们只观察到很小的结构变化，但由TIP5P模拟的团簇显示出比使用其他两种水模型的团簇更大百分比的分子具有低扩散系数，因为t->无穷大。随着温度的下降，TIP4P似乎比其他模型更有结构，形成了更多的氢键。冷却速率与实验结果吻合良好，蒸发速率与基于实验观察的唯象表达式吻合良好。(c)2006年，美国物理学会。
This paper presents a study on evaporation of pure water clusters. Molecular dynamics simulations between 20 ns and 3 mu s of clusters ranging from 125 to 4096 molecules in vacuum were performed. Three different models (SPC, TIP4P, and TIP5P) were used to simulate water, starting at temperatures of 250, 275, and 300 K. We monitored the temperature, the number of hydrogen bonds, the tetrahedral order, the evaporation, the radial distribution functions, and the diffusion coefficients. The three models behave very similarly as far as temperature and evaporation are concerned. Clusters starting at a higher temperature show a higher initial evaporation rate and therefore reach the point where evaporation stop (around 240 K) sooner. The radius of the clusters is decreased by 0.16-0.22 nm after 0.5 mu s (larger clusters tend to decrease their radius slightly more), which corresponds to around one evaporated molecule per nm(2). The cluster temperature seems to converge towards 215 K independent of cluster size, when starting at 275 K. We observe only small structural changes, but the clusters modeled by TIP5P show a larger percentage of molecules with low diffusion coefficient as t ->infinity, than those using the two other water models. TIP4P seems to be more structured and more hydrogen bonds are formed than in the other models as the temperature falls. The cooling rates are in good agreement with experimental results, and evaporation rates agree well with a phenomenological expression based on experimental observations. (c) 2006 American Institute of Physics.