该研究团队介绍了一种从XPCS研究中提取输运系数的方法，记为J(t)。该系数是非平衡统计力学中的一个基本参数，对于表征系统内的输运过程至关重要。这一方法统一了与各种输运系数相关的Green-Kubo公式，包括梯度流、粒子-粒子相互作用、摩擦矩阵和连续噪声。研究人员通过在马尔可夫链的框架内整合作用于粒子的随机和系统力的集体影响来实现这一点。研究人员最初通过分子动力学模拟系统温度随时间的变化来验证这种方法。
随后，他们使用文献中报道的实验系统进行了进一步的验证，并以其复杂的非平衡特性而闻名。结果，包括导出的J(t)和其他相关物理参数，与先前的观测结果一致，并揭示了非平衡状态下的详细动力学信息。这种方法代表了XPCS分析的进步，解决了日益增长的提取复杂非平衡动力学的需求。此外，所提出的方法与材料系统的性质无关，并且可以潜在地扩展到硬凝聚物质系统。
据悉，软凝聚态物质中的非平衡态需要系统的方法来表征和模拟材料，增强可预测性和应用。在这些工具中，X射线光子关联光谱(XPCS)提供了卓越的时间和空间分辨率，以提取对材料特性的动态洞察。然而，现有的模型可能忽略了复杂的细节。
附：英文原文
Title: Transport coefficient approach for characterizing nonequilibrium dynamics in soft matter
Author: He, HongRui, Liang, Heyi, Chu, Miaoqi, Jiang, Zhang, de Pablo, Juan J., Tirrell, Matthew V., Narayanan, Suresh, Chen, Wei
Issue&Volume: 2024-7-23
Abstract: Nonequilibrium states in soft condensed matter require a systematic approach to characterize and model materials, enhancing predictability and applications. Among the tools, X-ray photon correlation spectroscopy (XPCS) provides exceptional temporal and spatial resolution to extract dynamic insight into the properties of the material. However, existing models might overlook intricate details. We introduce an approach for extracting the transport coefficient, denoted as J(t), from the XPCS studies. This coefficient is a fundamental parameter in nonequilibrium statistical mechanics and is crucial for characterizing transport processes within a system. Our method unifies the Green–Kubo formulas associated with various transport coefficients, including gradient flows, particle–particle interactions, friction matrices, and continuous noise. We achieve this by integrating the collective influence of random and systematic forces acting on the particles within the framework of a Markov chain. We initially validated this method using molecular dynamics simulations of a system subjected to changes in temperatures over time. Subsequently, we conducted further verification using experimental systems reported in the literature and known for their complex nonequilibrium characteristics. The results, including the derived J(t) and other relevant physical parameters, align with the previous observations and reveal detailed dynamical information in nonequilibrium states. This approach represents an advancement in XPCS analysis, addressing the growing demand to extract intricate nonequilibrium dynamics. Further, the methods presented are agnostic to the nature of the material system and can be potentially expanded to hard condensed matter systems.
DOI: 10.1073/pnas.2401162121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2401162121