Computer Simulation of the Thermal Epitaxial Nucleation of Crystals

结晶是大量自然现象和技术过程的核心，包括结垢、新药生产和大气中冰的形成。晶体形成的最早阶段称为成核。成核可以控制晶体的关键特征，如其结构、方向和大小。尽管如此，我们对这些关键的成核事件的理解是穷人。晶体几乎总是在固体表面上成核，通常是总是存在的微观杂质的表面-没有真实的系统是100%不含所有杂质的。在表面上成核的过程称为非均质成核。大多数固体杂质颗粒将是晶体。因此，我们有一种晶体物质，它的一个晶格在另一个晶格上成核。如果两个晶格足够相似，则两个晶格可以彼此同步，这被称为外延成核。这被认为是为什么银碘化物在诱导水结晶方面如此出色的原因。然而，外延成核并没有得到很好的理解。在实验中，原子核的直径可能只有十亿分之几米，存在的时间也只有几分之一秒，因此从来没有被观察到过，我们将通过在计算机中研究成核来解决在实验中看不到原子核的问题。成核过程的计算机模拟可以从分子的角度观察成核过程。拟议的研究将尝试回答关于外延成核的基本但迄今尚未回答的问题，目的是了解哪些晶体表面有利于诱导结晶，哪些是坏的，以及为什么会这样。拟议的研究是进行第一个定量的计算机模拟研究的成核率和微观行为的晶体上的晶体的热成核的晶体基板。我们希望通过增加我们对外延成核的理解，在未来我们将能够更好地控制晶体的成核。结晶对我们很重要，原因有很多。通过雪的形成，它影响着我们的气候。此外，我们所依赖的许多材料都是结晶的，结晶是许多工业过程的核心。即使在您可能不期望的地方，结晶控制也很重要，例如在制药和巧克力制造中。我们希望回答的一些问题如下。如果我们改变表面的晶格和成核晶体的晶格之间的差异，成核的速度如何变化？已知如果两个晶格非常相似，则成核是快速的。此外，水晶表面有台阶和梯田。我们想知道：新的晶体是从表面的平坦部分开始还是从台阶开始？最后，所有固体的晶格都有缺陷，晶格不完美的地方。我们将看到在这些缺陷处成核是更快还是更慢。

Crystallisation lies at the heart of a vast array of natural phenomena and technological processes, including scale-formation, the production of new drugs, and the formation of ice in the atmosphere. The earliest stage of the formation of a crystal is called nucleation. Nucleation can control crucial features of a crystal, such as its structure, its orientation, and its size. Despite this, our understanding of these crucial nucleation events is poor. Crystals almost always nucleate on solid surfaces, usually the surfaces of the microscopic impurities that are always present - no real system is 100% free of all impurities. The process of nucleation on a surface is known as heterogeneous nucleation. Most solid impurity particles will be crystalline. Thus we have one crystalline substance with one crystal lattice nucleating on another with its own crystal lattice. If the two crystal lattices are sufficiently similar the two lattices can be in step with each other, this is called epitaxial nucleation. This is believed to be why silver iodide is so good at inducing at the crystallisation of water. However, epitaxial nucleation is not well understood. In experiment the nucleus is perhaps only a few billionths of a metre across and exists for a fraction of a second, and therefore has never been observed.We will get round the problem of not being able to see the nucleus in an experiment by studying nucleation in a computer. A computer simulation of nucleation can observe the nucleus forming in molecular detail. The proposed research will try and answer basic but so-far unanswered questions about epitaxial nucleation, with the aim of understanding which crystal surfaces are good at inducing crystallisation, and which are bad, and why this is. The proposed research is to undertake the first quantitative computer simulation study of the nucleation rates and microscopic behaviour of the thermal nucleation of a crystal on a crystalline substrate. We hope that by increasing our understanding of epitaxial nucleation, in the future we will be able to better control the nucleation of crystals. Crystallisation is important to us for many reasons. Through the formation of snow it affects our climate. Also, many of the materials we rely on are crystalline and crystallisation is at the hear of many industrial processes. Crystallisation control is important even in places where you might not expect it, for example in making both pharmaceuticals and chocolate.Some of the questions we hope to answer are as follows. How does the speed of nucleation vary if we vary the difference between the crystal lattice of the surface and that of the nucleating crystal? It is known that if the two lattices are very similar then nucleation is fast. Also, crystal surfaces have steps and terraces. We want to know: Does a new crystal start on a flat part of the surface or at a step? Finally, all solids have defects in their crystalline lattices, places where the lattice is not perfect. We will see if nucleation is faster or slower at these defects.