A Game of Order Parameters

对研究背景的简要描述，包括潜在的影响预测冰晶是否、如何以及何时会在云中形成(以及我们自己的细胞！)对大气科学(和低温保存！)很重要以及药品的制造。相反，在我们的大脑(蛋白质聚集体可能导致神经系统疾病)和石油工业(水基晶体可能堵塞管道)中，阻止晶体成核是可取的。原则上，计算机建模可以设计对这些过程进行最佳控制的策略：事实上，先进的原子模拟技术现在能够计算出晶体形核率等关键性质。不幸的是，这些比率与实验数据的比较受到不确定性的影响，还没有得到严格的量化。具体地说，我们用来将原子识别为晶核一部分的特定数学对象(所谓的“序参数”)的选择有很大的影响。我们将使用正式的不确定性量化(这是HETsys核心培训的一部分)来纠正这一点，首先使用简单的模型--可以获得准确的结果，然后进入具有非常实际重要性的场景--例如冰的形成。目的和目标本项目旨在通过计算机模拟来确定在计算晶体成核速率时，与特定序参数的选择有关的不确定性是什么。除了定量结果，我们还致力于开发一种可靠的方法，使我们能够以稳健和可重复的方式估计所述不确定性，从而为社区提供可靠的工具，以解释通过计算获得的成核率。此外，我们打算从相对简单的模型系统转移到现实场景，如冰的异质形成，这是一个激烈辩论的问题，在大气科学和低温保存等不同领域有无数实际回响。研究方法的新颖性计算晶体成核速率对分子模拟来说是一项具有挑战性的任务：因此，人们对与这些速率相关的不确定性知之甚少，该领域目前缺乏解决这一陷阱的强大方法。在这个项目中，我们将利用一系列不同的序参数来系统地研究它们对晶体形核率的影响。除了相对标准的技术(如委员分析)来探索这些顺序参数的可靠性，我们将利用贝叶斯推理来提供与特定顺序参数选择相关的错误的定量、前所未有的估计。与EPSRC的策略和研究领域保持一致这个项目非常适合计算和理论化学以及表面科学EPSRC领域。鉴于这项研究在冰核和生长背景下的深远影响，我们相信该项目有可能对EPSRC物理科学战略中强调的健康国家繁荣成果产生具体影响。参与该项目的任何公司或合作者都利用了广泛的合作网络，其中一些直接参与了最近授予的“现实世界的结晶”EPSRC计划拨款，包括几个英国机构；利兹、谢菲尔德、伦敦大学和华威。两位监督者都可以夸口说，现有的与冰和结晶直接相关的合作网络庞大，这势必会使拟议的研究产生最大影响。

Brief description of the context of the research including potential impactPredicting if, how and when ice crystals will form in clouds (and our own cells!) is important to atmospheric science (and cryopreservation!) and the manufacture of pharmaceuticals. Preventing crystals from nucleating is desirable instead in our brains (where aggregates of proteins can lead to neurological diseases) and for the oil industry (where water-based crystals can block pipelines). Computer modelling can, in principle, design strategies for optimal control over these processes: in fact, advanced atomistic simulation techniques are now able to calculate key properties such as crystal nucleation rates. Unfortunately, the comparison of these rates against experimental data is subject to uncertainties yet to be rigorously quantified. Specifically, the choice of the particular mathematical object we use to identify atoms as part of a crystalline nucleus (the so-called "order parameter") has a major impact. We will use formal uncertainty quantification (which form part of the core HETSYS training) to rectify this, initially using simple models - for which accurate results are available, and then moving onto scenarios of great practical importance - such as the formation of ice. Aims and objectivesThis project seeks to establish what is the uncertainty associated with the choice of a particular order parameter when computing crystal nucleation rate by means of computer simulations. Aside from quantitative results, we also aim to develop a reliable methodology that will allow us to estimate said uncertainty in a robust and reproducible fashion, so as to provide the community with a reliable tool to make sense of computationally obtained nucleation rates. In addition, we intend to move from relatively simple model systems to realistic scenarios such as the heterogeneous formation of ice, which is a hotly debated issue with countless practical reverberations across fields as diverse as atmospheric science and cryopreservation.Novelty of the research methodologyComputing crystal nucleation rates is a challenging task for molecular simulations: as such, very little is known about the uncertainty related to these rates, and the field is presently lacking a robust approach tackle this pitfall. In this project we will leverage an extensive array of different order parameters to systematically investigate their effect on crystal nucleation rates. On top of relatively standard techniques (such as committor analysis) to probe the reliability of these order parameters, we will harness Bayesian inference to provide quantitative, unprecedented estimates of the error associated with the choice of a specific order parameter.Alignment to EPSRC's strategies and research areasThis project fits very well within Computational and Theoretical Chemistry and Surface Science EPSRC Areas. Given the far-reaching implications of this research in the context of ice nucleation and growth, we believe the project has the potential to make a concrete impact with respect to the Healthy Nation prosperity outcome highlighted in the EPSRC strategy for the physical sciences.Any companies or collaborators involvedThe project leverages an extensive network of collaboration, some of which directly involved with the recently awarded "Crystallization in the Real World" EPSRC Program Grant, encompassing several UK institutions; Leeds, Sheffield, UCL as well as Warwick. The supervisors can both boast a large network of existing collaborations directly connected to ice and crystallization, which are bound to maximise the impact of the proposed research.