Spatial structure of unstable normal modes in a glass-forming liquid
Spatial structure of unstable normal modes in a glass-forming liquid
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DOI：
10.21468/scipostphys.10.1.001
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发表时间：
2021-01-01
期刊：
影响因子：
5.5
通讯作者：
Ikeda, Atsushi
中科院分区：
文献类型：
--
作者：
Shimada, Masanari;Coslovich, Daniele;Ikeda, Atsushi
玻璃形成液体的现象学通常是根据其潜在的高维势能面来描述的。特别是，作为温度的函数采样的固定点的统计数据提供了有用的洞察系统的热力学和动力学。然而，为了与真实的空间物理相联系，需要分析简正模的空间结构。在这项工作中，我们数值研究的势能面的玻璃形成三元混合物。从液体配置平衡在一个广泛的温度范围内使用交换蒙特卡罗方法，我们找到附近的固定点，并调查相关的不稳定模式的空间结构和能量。通过这种空间分辨的分析，最初开发研究局部极小值，我们证实了最近的证据表明，不稳定模式的性质从离域的模式耦合温度附近的本地化的变化。我们发现，离域模式的位移振幅有一个缓慢衰减的远场，而本地化模式包括一个大位移的核心和一个快速衰减的远场。迁移率边缘附近的不稳定模的分形维数等于1，与参与率的标度一致。最后，我们发现，周围和低于模式耦合温度的不稳定模式是本地化周围的结构缺陷，其特征在于由无序的局部结构显着不同的液体的局部有利的结构。这些缺陷与局部极小值中的准局部振动相关联，并且是预测低温下局部激发出现的良好候选者。
The phenomenology of glass-forming liquids is often described in terms of their underlying, high-dimensional potential energy surface. In particular, the statistics of stationary points sampled as a function of temperature provides useful insight into the thermodynamics and dynamics of the system. To make contact with the real space physics, however, analysis of the spatial structure of the normal modes is required. In this work, we numerically study the potential energy surface of a glass-forming ternary mixture. Starting from liquid configurations equilibrated over a broad range of temperatures using a swap Monte Carlo method, we locate the nearby stationary points and investigate the spatial architecture and the energetics of the associated unstable modes. Through this spatially-resolved analysis, originally developed to study local minima, we corroborate recent evidence that the nature of the unstable modes changes from delocalized to localized around the mode-coupling temperature. We find that the displacement amplitudes of the delocalized modes have a slowly decaying far field, whereas the localized modes consist of a core with large displacements and a rapidly decaying far field. The fractal dimension of unstable modes around the mobility edge is equal to 1, consistent with the scaling of the participation ratio. Finally, we find that around and below the mode-coupling temperature the unstable modes are localized around structural defects, characterized by a disordered local structure markedly different from the liquid's locally favored structure. These defects are similar to those associated to quasi-localized vibrations in local minima and are good candidates to predict the emergence of localized excitations at low temperature.