该课题组处理了一个表现出较快过程（Johari-Goldstein β松弛）的非对称二聚体系统，并采用平行淬火法来访问低温区间。这些费力的努力使他们能够详细研究势能景貌并揭示了诱导β松弛的地形层次结构的第一手直接证据。此外，他们还成功地表征了每个松弛过程中颗粒的微观运动。最后，他们研究了低频模式与两个松弛过程之间的相关性。这些研究结果建立了实验观察到的超冷液体松弛动力学的基本和全面的理解。
据了解，超冷液体的结构松弛过程一直是凝聚态物理实验和理论方面的难点。过去的实验广泛观察到在低温下松弛动力学分为两个不同的过程，而许多种分子液体都出现了这种现象。其中一个可能的解释是这种分离源于势能景貌的两级分层地形，但尚未得到证实。为了解决这个问题，分子动力学模拟是一种有前途的方法。然而，要克服两个困难：首先，我们必须处理一个计算量大的分子液体模型，这与已经广泛研究但只显示出较慢过程（α松弛）的简单球形模型相比，需要更高的计算资源。其次，我们必须达到足够低的温度区间，使得两个过程能够明显分离。
附：英文原文
Title: Johari–Goldstein β relaxation in glassy dynamics originates from two-scale energy landscape
Author: Shiraishi, Kumpei, Mizuno, Hideyuki, Ikeda, Atsushi
Issue&Volume: 2023-3-29
Abstract: Supercooled liquids undergo complicated structural relaxation processes, which have been a long-standing problem in both experimental and theoretical aspects of condensed matter physics. In particular, past experiments widely observed for many types of molecular liquids that relaxation dynamics separated into two distinct processes at low temperatures. One of the possible interpretations is that this separation originates from the two-scale hierarchical topography of the potential energy landscape; however, it has never been verified. Molecular dynamics simulations are a promising approach to tackle this issue, but we must overcome laborious difficulties. First, we must handle a model of molecular liquids that is computationally demanding compared to simple spherical models, which have been intensively studied but show only a slower process: α relaxation. Second, we must reach a sufficiently low-temperature regime where the two processes become well-separated. Here, we handle an asymmetric dimer system that exhibits a faster process: Johari–Goldstein β relaxation. Then, we employ the parallel tempering method to access the low-temperature regime. These laborious efforts enable us to investigate the potential energy landscape in detail and unveil the first direct evidence of the topographic hierarchy that induces the β relaxation. We also successfully characterize the microscopic motions of particles during each relaxation process. Finally, we study the correlation between low-frequency modes and two relaxation processes. Our results establish a fundamental and comprehensive understanding of experimentally observed relaxation dynamics in supercooled liquids.
DOI: 10.1073/pnas.2215153120
