Complex Metastable Liquids: Phase Behaviour, Dynamics, and Nucleation

复杂亚稳态液体：相行为，动力学和成核******液体状态是我们对物质理解的持久挑战。即使是最简单的经典液体也是致密的、无序的、强相互作用的多体系统。因此，液体呈现给我们丰富的行为和令人敬畏的复杂性，尤其是在分子尺度上。******液态物理学中一些最重要和最令人困惑的开放性问题发生在过冷液体中。非晶态固体在玻璃化转变过程中形成的性质一直是争论的焦点。同样，从液态到结晶固体的成核也不完全清楚；例如，对于许多重要的体系，我们定量准确地预测晶体成核速率的能力仍然很差。虽然所有这些问题都是基本性质的，但实际应用比比皆是。例如，金属玻璃合金是一个日益增长的商业兴趣领域，例如用于飞机部件。了解晶体成核在从计算机芯片到制药等广泛的制造业中至关重要。******在过冷液体的背景下，许多不同而复杂的现象汇聚在一起：亚稳相的热力学；粘性液体的复杂动力学特性；以及晶体成核的非平衡动力学。该提案描述了一个研究计划，以调查过冷液体，重点关注水的成核现象，因为它的复杂性，以及它在自然科学和工程中的普遍重要性。同时，我们将寻求在上述所有复杂现象交织在一起的条件下研究物质，以寻求对亚稳态系统的更广泛理解。******我们将使用分子动力学和蒙特卡罗计算机模拟，从中可以获得分子尺度的细节和体积性质的估计。例如，相图和成核的自由能势垒将使用伞形采样方法进行评估，稀有事件模拟技术，如正向通量采样，将有助于计算成核速率。我们选择的研究方向是为了提供广泛的科学兴趣的结果，并创造训练机会，为学生将来在定量科学领域的工作做好准备。例如，我们将研究深度过冷水中的冰核，接近于在计算机模拟中观察到的提出的液-液相变。我们还将研究具有明显迁移率波动（即动态非均质）的系统中的晶体成核，以探索成核和玻璃形成之间的联系。我们还将研究非均质成核，特别是在水中，因为这一过程对于理解云形成对气候模拟的贡献很重要。

Complex Metastable Liquids: Phase Behaviour, Dynamics, and Nucleation******The liquid state is an enduring source of challenges for our understanding of matter. Even the simplest classical liquid is a dense, disordered, and strongly-interacting many-body system. Liquids thus present us with rich behavior and formidable complexity, especially at the molecular scale.******Some of the most important and perplexing open questions in liquid-state physics occur in supercooled liquids. The nature of amorphous solid formation at the glass transition is a continuing source of debate. Similarly, the nucleation of crystalline solids from the liquid state is also incompletely understood; e.g. our ability to predict crystal nucleation rates with quantitative accuracy remains poor for many important systems. While all these questions are of a fundamental nature, practical applications abound. For example, metallic glass alloys are a growing area of commercial interest, e.g. for aircraft components. Understanding crystal nucleation is vital in a wide swathe of manufacturing, from computer chips to pharmaceuticals.******In the context of supercooled liquids, a number of distinct and complex phenomena converge: the thermodynamics of metastable phases; the complex dynamic properties of viscous liquids; and the non-equilibrium kinetics of crystal nucleation. This proposal describes a program of research to investigate supercooled liquids, with a focus on nucleation phenomena in water, because of its complexity, and its pervasive importance across the natural sciences and engineering. At the same time, we will seek to study substances under conditions in which all the complex phenomena listed above become intertwined, in order to seek a broader understanding of metastable systems.******We will use molecular dynamics and Monte Carlo computer simulations, from which both molecular-scale details and estimates of bulk properties may be obtained. For example, phase diagrams and free energy barriers for nucleation will be evaluated using umbrella sampling methods, and rare-event simulation techniques such as forward-flux sampling will facilitate calculation of nucleation rates. Our research directions are chosen to provide results of wide scientific interest, and to create training opportunities that prepare students for future work in the quantitative sciences. For example, we will study ice nucleation in deeply supercooled water, close to the proposed liquid-liquid phase transition that has been observed in computer simulations. We will also examine crystal nucleation in systems exhibiting pronounced mobility fluctuations (i.e. dynamical heterogeneities) to explore connections between nucleation and glass formation. We will also study heterogeneous nucleation, especially in water, due to the importance of this process for understanding the contributions of cloud formation to climate modeling.