Dipartimento di Fisica Enrico Fermi, Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy.
J Chem Phys. 2012 Jun 7;136(21):211101. doi: 10.1063/1.4725522.
The violation of the Stokes-Einstein (SE) law is investigated in a melt of linear chains by extensive molecular-dynamics simulations. It is found that the SE breakdown is signaled (with 5% uncertainty) by the monomer mean-square displacement <u(2)> on the picosecond time scale. On this time scale the displacements of the next-next-nearest neighbors are uncorrelated. It is shown that: (i) the SE breakdown occurs when <u(2)> is smaller than the breadth of the distribution of the square displacements to escape from the first-neighbors cage, (ii) the dynamical heterogeneity affects the form of the master curve of the universal scaling between the structural relaxation and <u(2)>.
通过广泛的分子动力学模拟研究了线性链熔体中的 Stokes-Einstein（SE）定律违反情况。结果发现，单体均方位移 <u(2)> 在皮秒时间尺度上出现信号（不确定性为 5%），表明 SE 破坏。在这个时间尺度上，下一个次近邻的位移是不相关的。结果表明：（i）当 <u(2)> 小于逃脱第一近邻笼的平方位移分布的宽度时，SE 破坏发生；（ii）动力学异质性影响结构弛豫和 <u(2)> 之间普遍标度的主曲线形式。
