动力学非均匀性与Stokes-Einstein和 模拟水中的Stokes-Einstein-Debye关系

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摘要翻译：
我们用扩展的简单水点电荷模型的分子动力学模拟研究了Stokes-Einstein(SE)和Stokes-Einstein-Debye(SED)关系。我们发现SE和SED关系在低温下都破裂了。为了探讨这些分解与动力异质性(DH)之间的关系，我们还计算了7%“最快”和7%“最慢”分子子集的SE和SED关系。我们发现SE和SED关系在两个子集中都发生了崩溃，并且这种崩溃发生在所有的迁移率尺度上。因此，这些崩溃似乎是普遍的现象，这与这样一种观点形成了对比，即只有最流动的分子才是SE和SED关系崩溃的根源，这种关系存在于一个不活跃的背景中。在低温下，这两个分子子集中的SE和SED关系都被“分数”SE和SED关系取代，即$D_T\sim(\tau/t)^{-\xi_t}$和$D_R\sim(\tau/t)^{-\xi_r}$,其中$\xi_t约0.84<1$和$\xi_r约0.75<1$。我们还发现在旋转和平移运动之间存在解耦，这种解耦发生在最快和最慢的分子子集中。我们还发现，当解耦增加时，在冷却时，分子被归类为平移和旋转最快的概率也增加了。为了研究时间尺度对SE和SED击穿和解耦的影响，我们引入了SE和SED关系的时间依赖版本，以及测量解耦程度的时间依赖函数。我们的结果表明，解耦和SE、SED分解都是在与笼型体系结束相对应的时间尺度上产生的，当扩散开始时。这也是DH更相关的时间尺度。
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英文标题：
《Dynamical heterogeneities and the breakdown of the Stokes-Einstein and
  Stokes-Einstein-Debye relations in simulated water》
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作者：
Marco G. Mazza, Nicolas Giovambattista, H.Eugene Stanley, Francis W.
  Starr
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最新提交年份：
2007
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分类信息：

一级分类：Physics        物理学
二级分类：Statistical Mechanics        统计力学
分类描述：Phase transitions, thermodynamics, field theory, non-equilibrium phenomena, renormalization group and scaling, integrable models, turbulence
相变，热力学，场论，非平衡现象，重整化群和标度，可积模型，湍流
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一级分类：Physics        物理学
二级分类：Soft Condensed Matter        软凝聚态物质
分类描述：Membranes, polymers, liquid crystals, glasses, colloids, granular matter
膜，聚合物，液晶，玻璃，胶体，颗粒物质
--

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英文摘要：
  We study the Stokes-Einstein (SE) and the Stokes-Einstein-Debye (SED) relations using molecular dynamics simulations of the extended simple point charge model of water. We find that both the SE and SED relations break down at low temperature. To explore the relationship between these breakdowns and dynamical heterogeneities (DH), we also calculate the SE and SED relations for subsets of the 7% ``fastest'' and 7% ``slowest'' molecules. We find that the SE and SED relations break down in both subsets, and that the breakdowns occur on all scales of mobility. Thus these breakdowns appear to be generalized phenomena, in contrast with the view where only the most mobile molecules are the origin of the breakdown of the SE and SED relations, embedded in an inactive background where these relations hold. At low temperature, the SE and SED relations in both subsets of molecules are replaced with ``fractional'' SE and SED relations, $D_t\sim(\tau/T)^{-\xi_t}$ and $D_r\sim(\tau/T)^{-\xi_r}$ where $\xi_t\approx0.84<1$ and $\xi_r\approx0.75<1$. We also find that there is a decoupling between rotational and translational motion, and that this decoupling occurs in both fastest and slowest subsets of molecules. We also find that when the decoupling increases, upon cooling, the probability of a molecule being classified as both translationally and rotationally fastest also increases. To study the effect of time scale for SE and SED breakdown and decoupling, we introduce a time-dependent version of the SE and SED relations, and a time-dependent function that measures the extent of decoupling. Our results suggest that both the decoupling and SE and SED breakdowns are originated at the time scale corresponding to the end of the cage regime, when diffusion starts. This is also the time scale when the DH are more relevant.
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PDF链接：
https://arxiv.org/pdf/705.4475

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关键词：Einstein Stein TEI sto 动力学 发现 结束 tau 动力学