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Characterising and Controlling Rare Event Dynamics

表征和控制罕见事件动态

基本信息

批准号：
EP/H042660/1
负责人：
David John Wales
金额：
$ 59.68万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FH042660%2F1
关键词：
Characterising Controlling Rare Event Dynamics

项目摘要

Theory and simulation are cornerstones of molecular science, guiding, informing, and interpreting experiments. Some simulations are performed to test the practicality of costly laboratory work, while other calculations may provide information that is not accessible experimentally. Applications cover a diverse range of activities, from drug design in the pharmaceutical industry, through surface catalysis, to predicting the behaviour of soft matter in materials such as liquid crystals, which are used in display technology.For computer simulations to be useful we must achieve some level of confidence in the predictions that are made. Achieving useful accuracy depends on both a sufficiently faithful representation of the interatomic or intermolecular interactions, and on whether the calculated quantities reflect the conditions of the experiment in a statistically meaningful way. Our proposal addresses the latter issue, namely how to sample events of interest that rarely occur on the accessible time scale of simulations. Calculating a meaningful average for some property of interest is impossible for many problems of great contemporary importance using conventional methods. Examples include chemical reactions and changes of structure or phase that correspond to a large barrier on the potential or free energy surface. Conventional simulations of such systems will spend all or most of the available computer time waiting for the barrier to be crossed, and may miss the key transition entirely. More sophisticated simulation techniques are therefore needed, which sample the events of interest directly.Various complementary approaches have been suggested to address this rare events problem and extend computer simulations to larger systems and longer time scales. We propose to combine two of the most successful methods, one that is based on geometry optimisation, and the other on explicit dynamics, to produce a hybrid methodology that is efficient enough to treat mesoscopic problems. The geometry optimisation approach can treat events that are arbitrarily slow, because the barriers in question are calculated directly. Rate constants can then be evaluated using well known tools from unimolecular rate theory, which involves a series of approximations. By combining the pathways determined by geometry optimisation with explicit dynamics we aim to produce much more accurate rate constants and extend the domain accessible to simulation to treat far more complex systems.Two important applications will be considered. First we will analyse the pathways for nucleation in a wide variety of bulk systems, including models that form glasses, liquid crystals, and granular material. Our most ambitious objective is to use this knowledge to gain kinetic control of nucleation. The ability to predict the outcome of nucleation, and change conditions accordingly, would be immediately useful to pharmaceutical companies and to the manufacture of materials based upon glasses or liquid crystals. The ability to describe and predict the ageing properties of glassy materials will immediately find a number of important applications.The second application we would consider involves the design of a molecular motor from mesoscopic building blocks. Here we would seek to determine general design principles that govern the efficiency of converting chemical energy into available work. Hence we would guide experiments in the choice of molecular components to produce an efficient motor, including characteristics of the intermolecular interaction governed by shape, charge, etc.

理论和模拟是分子科学的基石，指导、提供信息和解释实验。进行一些模拟是为了测试昂贵的实验室工作的实用性，而其他计算可能提供实验无法获得的信息。应用范围广泛，从制药业的药物设计，到表面催化，再到预测显示技术中使用的液晶等材料中软物质的行为。为了使计算机模拟有用，我们必须对所作的预测有一定程度的信心。实现有用的准确性取决于原子间或分子间相互作用的足够忠实的表示，以及计算量是否以统计上有意义的方式反映实验条件。我们的建议解决了后一个问题，即如何对在模拟的可访问时间尺度上很少发生的感兴趣的事件进行采样。对于许多具有当代重大意义的问题，用传统方法计算某一特性的有意义的平均值是不可能的。例子包括化学反应和结构或相的变化，对应于一个大的势垒或自由能表面。这种系统的传统模拟将花费所有或大部分可用的计算机时间来等待跨越障碍，并且可能完全错过关键转换。因此需要更复杂的模拟技术，直接对感兴趣的事件进行采样。已经提出了各种补充方法来解决这一罕见事件问题，并将计算机模拟扩展到更大的系统和更长的时间尺度。我们建议结合两种最成功的方法，一种基于几何优化，另一种基于显式动力学，以产生一种混合方法，足以有效地处理介观问题。几何优化方法可以处理任意缓慢的事件，因为所讨论的障碍是直接计算的。然后可以使用单分子速率理论中众所周知的工具来评估速率常数，这涉及到一系列的近似。通过将几何优化确定的路径与显式动力学相结合，我们的目标是产生更准确的速率常数，并扩展可用于模拟的领域，以处理更复杂的系统。我们将考虑两个重要的应用。首先，我们将分析各种散装系统中成核的途径，包括形成玻璃，液晶和颗粒材料的模型。我们最雄心勃勃的目标是利用这些知识获得成核的动力学控制。预测成核结果并相应地改变条件的能力，对制药公司和基于玻璃或液晶的材料的制造将立即有用。描述和预测玻璃材料的老化特性的能力将立即找到许多重要的应用。我们将考虑的第二个应用涉及从介观构建块设计分子马达。在这里，我们将设法确定控制将化学能转化为可用功的效率的一般设计原则。因此，我们将指导实验在分子成分的选择，以产生一个有效的马达，包括分子间相互作用的特征，由形状，电荷等控制。