过冷液体的Stokes-Einstein关系和动力学不均匀

Stokes-Einstein（SE）关系是涨落-耗散定理的特例，联系着在液体中运动的粒子的扩散系数和摩擦系数。过冷液体作为桥梁连接着普通液体和晶体、玻璃态，其本身处于亚稳态。然而近期的研究指出由于动力学不均匀，过冷液体中的SE关系不成立。此结论基于一系列假设下的SE关系的替代形式，并未从原始形式出发，因而SE关系在过冷液体中成立与否仍存疑。另外无论是动力学不均匀本身的机制，还是与SE关系及其替代形式间的联系仍待阐明。鉴于分子动力学模拟在直接观察粒子的运动和计算复杂的关联函数上的优势，我们拟采用分子动力学模拟并结合理论分析，系统地研究过冷液体直至玻璃转变点附近的SE关系和动力学不均匀，确定SE关系对过冷液体的适用性以及其替代形式的合理性，从关联和结构上揭示动力学不均匀的来源，定性并定量地阐明动力学不均匀和SE关系及其替代形式之间的关系。

The Stokes-Einstein (SE) relation is a special case of the fluctuation-dissipation theorem, which relates the diffusion constant and frictional coefficient of particles moving in a liquid. Supercooled liquids connect normal liquids and crystals or glassy states; and it is in a metastable state. Recent studies have pointed out that the SE relation is invalid in supercooled liquids due to the dynamic heterogeneity. However, the conclusion is based on the variants of the SE relation under a series of assumption and is not started from its original form. Therefore, whether the SE relation is valid or not for supercooled liquids is still in elusive. Moreover, the mechanism of dynamic heterogeneity still needs to be explored as well as the connections among dynamic heterogeneity, SE relation and its variants. In view of the advantages of molecular dynamics simulation to directly capture particle dynamics and calculate complex correlation functions, we will adopt molecular dynamics simulation combined with theory to systematically study the SE relation and dynamic heterogeneity of supercooled liquids to the vicinity of the glass transition point, so as to determine the applicability of the SE relation to supercooled liquids and the rationality of its variants, to reveal the mechanism of dynamical heterogeneity from correlations and structures, to explore the qualitative and quantitative relations between dynamical heterogeneity and SE relation as well as its variants.