Using classical as well as ab initio molecular dynamics simulations, we calculate the frequency-dependent shear viscosity of pure water and water–glycerol mixtures. In agreement with recent experiments, we find deviations from Newtonian-fluid behavior} in the THz regime. Based on an extension of the Maxwell model, we introduce a viscoelastic model} to describe the observed viscosity spectrum of pure water. We find four relaxation modes in the spectrum which we attribute to i) hydrogen–bond network topology changes, ii) hydrogen–bond stretch vibrations of water pairs, iii) collective vibrations of water molecule triplets, and iv) librational excitations of individual water molecules. Our model quantitatively describes the viscoelastic response of liquid water on short timescales, where the hydrodynamic description via a Newtonian-fluid model breaks down.

中文翻译：

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高频液态水非牛顿粘弹性行为的分子解释

使用经典的和从头算的分子动力学模拟，我们计算了纯水和水-甘油混合物的频率相关剪切粘度。与最近的实验一致，我们发现在太赫兹范围内与牛顿流体行为的偏差。在麦克斯韦模型的扩展基础上，我们引入了粘弹性模型来描述观察到的纯水的粘度谱。我们在频谱中发现了四种弛豫模式，这些模式可归因于：i）氢键网络拓扑变化，ii）水对的氢键拉伸振动，iii）水分子三重态的集体振动以及iv）单个水分子的自由激发。我们的模型定量描述了液态水在短时间内的粘弹性响应，