Sun Peihao, Hastings J B, Ishikawa Daisuke, Baron Alfred Q R, Monaco Giulio
SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States.
Physics Department, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, United States.
J Phys Chem B. 2021 Dec 16;125(49):13494-13501. doi: 10.1021/acs.jpcb.1c07900. Epub 2021 Dec 2.
Despite the technological importance of supercritical fluids, controversy remains about the details of their microscopic dynamics. In this work, we study four supercritical fluid systems─water, Si, Te, and Lennard-Jones fluid─via classical molecular dynamics simulations. A universal two-component behavior is observed in the intermolecular dynamics of these systems, and the changing ratio between the two components leads to a crossover from liquidlike to gaslike dynamics, most rapidly around the Widom line. We find evidence to connect the liquidlike component dominating at lower temperatures with intermolecular bonding and the component prominent at higher temperatures with free-particle, gaslike dynamics. The ratio between the components can be used to describe important properties of the fluid, such as its self-diffusion coefficient, in the transition region. Our results provide an insight into the fundamental mechanism controlling the dynamics of supercritical fluids and highlight the role of spatiotemporally inhomogeneous dynamics even in thermodynamic states where no large-scale fluctuations exist in the fluid.
尽管超临界流体在技术上具有重要性，但关于其微观动力学的细节仍存在争议。在这项工作中，我们通过经典分子动力学模拟研究了四种超临界流体系统——水、硅、碲和 Lennard-Jones 流体。在这些系统的分子间动力学中观察到一种普遍的双组分行为，并且这两种组分之间变化的比例导致了从类液体动力学向类气体动力学的转变，在 Widom 线附近最为迅速。我们发现有证据将低温下占主导的类液体组分与分子间键合联系起来，将高温下突出的组分与自由粒子、类气体动力学联系起来。在过渡区域，组分之间的比例可用于描述流体的重要性质，例如其自扩散系数。我们的结果深入了解了控制超临界流体动力学的基本机制，并突出了即使在流体中不存在大规模涨落的热力学状态下时空不均匀动力学的作用。
