Verde Alejandro R, Alarcón Laureano M, Appignanesi Gustavo A
INQUISUR, Departamento de Química, Universidad Nacional del Sur (UNS)-CONICET, Avenida Alem 1253, 8000 Bahía Blanca, Argentina.
J Chem Phys. 2023 Mar 21;158(11):114502. doi: 10.1063/5.0139118.
A salient feature of supercooled liquids consists in the dramatic dynamical slowdown they undergo as temperature decreases while no significant structural change is evident. These systems also present dynamical heterogeneities (DH): certain molecules, spatially arranged in clusters, relax various orders of magnitude faster than the others. However, again, no static quantity (such as structural or energetic measures) shows strong direct correlations with such fast-moving molecules. In turn, the dynamic propensity approach, an indirect measure that quantifies the tendency of the molecules to move in a given structural configuration, has revealed that dynamical constraints, indeed, originate from the initial structure. Nevertheless, this approach is not able to elicit which structural quantity is, in fact, responsible for such a behavior. In an effort to remove dynamics from its definition in favor of a static quantity, an energy-based propensity has also been developed for supercooled water, but it could only find positive correlations between the lowest-energy and the least-mobile molecules, while no correlations could be found for those more relevant mobile molecules involved in the DH clusters responsible for the system's structural relaxation. Thus, in this work, we shall define a defect propensity measure based on a recently introduced structural index that accurately characterizes water structural defects. We shall show that this defect propensity measure provides positive correlations with dynamic propensity, being also able to account for the fast-moving molecules responsible for the structural relaxation. Moreover, time dependent correlations will show that defect propensity represents an appropriate early-time predictor of the long-time dynamical heterogeneity.
过冷液体的一个显著特征在于，随着温度降低，它们会经历显著的动力学减速，而此时并无明显的结构变化。这些系统还呈现出动力学非均匀性（DH）：某些分子在空间上聚集成簇，其弛豫速度比其他分子快几个数量级。然而，同样地，没有任何静态量（如结构或能量度量）与这些快速移动的分子呈现出强直接相关性。相应地，动态倾向方法作为一种间接度量，用于量化分子在给定结构构型中移动的倾向，它揭示了动力学约束实际上源自初始结构。尽管如此，这种方法无法确定究竟是哪个结构量导致了这种行为。为了在定义中排除动力学因素而倾向于使用静态量，人们还为过冷水开发了基于能量的倾向，但它只能发现最低能量分子与最不活跃分子之间的正相关性，而对于那些参与系统结构弛豫的DH簇中更相关的活跃分子，却找不到相关性。因此，在这项工作中，我们将基于最近引入的一种能准确表征水结构缺陷的结构指数来定义一种缺陷倾向度量。我们将表明，这种缺陷倾向度量与动态倾向呈现出正相关性，并且还能够解释导致结构弛豫的快速移动分子。此外，随时间变化的相关性将表明，缺陷倾向是长时间动力学非均匀性的一个合适的早期预测指标。
