Goree J, Donkó Z, Hartmann P
Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Jun;85(6 Pt 2):066401. doi: 10.1103/PhysRevE.85.066401. Epub 2012 Jun 11.
Because liquids cannot resist shear except over very short distances comparable to the atomic spacing, shear sound waves (i.e., transverse phonons) propagate only for very short wavelengths. A measure of this limit is the cutoff wave number k(c), which is sometimes called the critical wave number. Previously k(c) was determined in molecular dynamics (MD) simulations by obtaining the dispersion relation. Another approach is developed in this paper by identifying the wave number at the onset of a negative peak in the transverse current correlation function. This method is demonstrated using a three-dimensional MD simulation of a Yukawa fluid, which mimics dusty plasmas. In general, k(c) is an indicator of conditions where elastic and dissipative effects are approximately balanced. Additionally, the crossover frequency for the real and imaginary terms of the complex viscosity of a dusty plasma is obtained; this crossover frequency corresponds to the Maxwell relaxation time.
由于液体除了在与原子间距相当的极短距离内无法抵抗剪切力，剪切声波（即横向声子）仅在非常短的波长下传播。这个极限的一个度量是截止波数k(c)，它有时也被称为临界波数。以前，k(c)是通过在分子动力学（MD）模拟中获得色散关系来确定的。本文通过识别横向电流相关函数中负峰开始时的波数，开发了另一种方法。使用模仿尘埃等离子体的 Yukawa 流体的三维 MD 模拟来演示此方法。一般来说，k(c)是弹性和耗散效应大致平衡的条件的一个指标。此外，还获得了尘埃等离子体复粘度实部和虚部的交叉频率；这个交叉频率对应于麦克斯韦弛豫时间。
