Egami Takeshi, Shinohara Yuya
Department of Materials Science and Engineering, and Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
J Chem Phys. 2020 Nov 14;153(18):180902. doi: 10.1063/5.0024013.
In liquids, the timescales for structure, diffusion, and phonon are all similar, of the order of a pico-second. This not only makes characterization of liquid dynamics difficult but also renders it highly questionable to describe liquids in these terms. In particular, the current definition of the structure of liquids by the instantaneous structure may need to be expanded because the liquid structure is inherently dynamic. Here, we advocate describing the liquid structure through the distinct-part of the Van Hove function, which can be determined by inelastic neutron and x-ray scattering measurements as well as by simulation. It depicts the dynamic correlation between atoms in space and time, starting with the instantaneous correlation function at t = 0. The observed Van Hove functions show that the atomic dynamics is strongly correlated in some liquids, such as water. The effect of atomic correlation on various transport properties of fluid, including viscosity and diffusivity, is discussed.
在液体中，结构、扩散和声子的时间尺度都相似，约为皮秒量级。这不仅使得表征液体动力学变得困难，而且用这些术语来描述液体也极具疑问。特别是，目前通过瞬时结构对液体结构的定义可能需要扩展，因为液体结构本质上是动态的。在这里，我们主张通过范霍夫函数的独特部分来描述液体结构，它可以通过非弹性中子和X射线散射测量以及模拟来确定。它描述了原子在空间和时间上的动态关联，从t = 0时的瞬时关联函数开始。观察到的范霍夫函数表明，在某些液体中，如水中，原子动力学具有很强的相关性。讨论了原子关联对流体各种传输性质（包括粘度和扩散率）的影响。
