论文标题
单个粒子波动主导着玻璃形成液体的长期动态敏感性
Single particle fluctuations dominate the long-time dynamic susceptibility in glass-forming liquids
论文作者
论文摘要
玻璃过渡附近的液体表现出动态异质性，即液体中的相关区域以比平均水平快得多的速度或速度慢得多。这种集体现象的特征是测量动态敏感性$χ_4（t）$，有时会根据那些放松区域的大小和波动强度来解释。我们表明，这些测量结果的结果不仅会受到弛豫率的集体波动的影响，而且还会受到初始状态和单粒子波动的密度波动的影响。我们还表明，很长一段时间以来，平均重叠$ c（t）$探测了由时间间隔$ t $衰减的初始状态和最终状态之间的相似性，因为$ c（t）\ sim t）\ sim t^{ - d/2} $。这比拉伸指数行为$ c（t）\ sim {\ rm e}^{ - （t/τ）^β} $先前在$α$ - 递减时间的一两个数量级以内$α$ - 递减时间$τ_α$。我们发现，在$ 10-100τ_α$的时间内，动态敏感性$χ_4（t）$由单个粒子波动主导，而$χ_4（t）\ c（t）\ oft c（t）\ sim t^{ - d/2} $。最后，我们通过减去单粒子波动和初始状态密度波动的效果来提出一种为动态敏感性$χ_4（t）$提取集体放松贡献的方法。我们将此方法应用于两个形成玻璃模型的数值模拟：二进制硬球系统和一个Kob-Andersen Lennard-Jones系统。这使我们能够将数值数据的分析扩展到比以前可能更长的时间尺度，并为动态异质性研究（包括确定交换时间的确定）打开了进一步的进展。
Liquids near the glass transition exhibit dynamical heterogeneity, i.e. correlated regions in the liquid relax at either a much faster rate or a much slower rate than the average. This collective phenomenon has been characterized by measurements of a dynamic susceptibility $χ_4(t)$, which are sometimes interpreted in terms of the size of those relaxing regions and the intensity of the fluctuations. We show that the results of those measurements can be affected not only by the collective fluctuations in the relaxation rate, but also by density fluctuations in the initial state and by single-particle fluctuations. We also show that at very long times the average overlap $C(t)$ probing the similarity between an initial and a final state separated by a time interval $t$ decays as a power law $C(t) \sim t^{-d/2}$. This is much slower than the stretched exponential behavior $C(t) \sim {\rm e}^{-(t/τ)^β}$ previously observed at times within one or two orders of magnitude of the $α$-relaxation time $τ_α$. We find that for times longer than $10-100 τ_α$, the dynamic susceptibility $χ_4(t)$ is dominated by single particle fluctuations, and that $χ_4(t) \approx C(t) \sim t^{-d/2}$. Finally, we introduce a method to extract the collective relaxation contribution to the dynamic susceptibility $χ_4(t)$ by subtracting the effects of single-particle fluctuations and initial state density fluctuations. We apply this method to numerical simulations of two glass forming models: a binary hard sphere system and a Kob-Andersen Lennard-Jones system. This allows us to extend the analysis of numerical data to timescales much longer than previously possible, and opens the door for further future progress in the study of dynamic heterogeneities, including the determination of the exchange time.
