Classification of mobile- and immobile-molecule timescales for the Stokes-Einstein and Stokes-Einstein-Debye relations in supercooled water
Classification of mobile- and immobile-molecule timescales for the Stokes-Einstein and Stokes-Einstein-Debye relations in supercooled water
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过冷水中斯托克斯-爱因斯坦和斯托克斯-爱因斯坦-德拜关系的移动和固定分子时间尺度的分类
DOI：
10.1088/1742-5468/ab3114
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Takeshi Kawasaki and Kang Kim
中科院分区：
文献类型：
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作者：
Ikeda Atsushi;Kawasaki Takeshi;Berthier Ludovic;Saitoh Kuniyasu;Hatano Takahiro;Takeshi Kawasaki and Kang Kim;Takeshi Kawasaki and Kang Kim
采用分子动力学方法对TIP 4P/2005过冷水进行了模拟，研究了不同时间尺度下的分子扩散和剪切粘度，并分析了Stokes-Einstein（SE）和Stokes-Einstein-Debye（SED）关系.为此，我们计算了各种时间相关函数，如均方位移，应力松弛函数，密度相关函数，氢键相关函数，分子取向的旋转相关函数，非高斯参数，和四点相关函数。我们的SE和SED关系的研究表明，使用这些时间相关函数得到的输运系数和时间尺度可以分为两个不同的类：那些由移动的或im移动的分子，由于动力学的异质性。特别是，我们表明，应力弛豫时间，氢键寿命，和大角度旋转弛豫时间与平移扩散耦合，其特征在于移动的分子。与此相反，结构弛豫时间，小角度旋转弛豫时间，四点相关函数的特征时间尺度与平移扩散解耦，并由不动分子。这种解耦导致违反SE关系。这些结果表明，适当表征传输系数，如平移扩散常数和剪切粘度的时间尺度的识别，提供了一个深刻的洞察到违反的SE和SED的关系在玻璃形成液体。
Molecular dynamics simulations have been performed on TIP4P/2005 supercooled water to investigate the molecular diffusion and shear viscosity at various timescales and assess the Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations. For this purpose, we calculated various time correlation functions, such as the mean-squared displacement, stress relaxation function, density correlation function, hydrogen-bond correlation function, rotational correlation function of molecular orientation, non-Gaussian parameter, and four-point correlation function. Our study of the SE and SED relations indicates that the transport coefficients and timescales obtained using these time correlation functions may be classified into two distinct classes: those governed by either mobile or immobile molecules, due to dynamical heterogeneity. In particular, we show that the stress relaxation time, hydrogen-bond lifetime, and large-angle rotational relaxation time are coupled with translational diffusion, and are characterized by mobile molecules. In contrast, the structural-relaxation time, small-angle rotational relaxation time, and characteristic timescales of four-point correlation functions are decoupled with translational diffusion, and are governed by immobile molecules. This decoupling results in a violation of the SE relation. These results indicate that the identification of timescales that appropriately characterize transport coefficients, such as translational diffusion constant and shear viscosity, provides a deep insight into the violation of the SE and SED relations in glass-forming liquids.