Characterising and Controlling Rare Event Dynamics

理论和模拟是分子科学的基石，指导，通知和解释实验。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，从制药工业中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，我们必须对所做的预测具有一定程度的信心。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，以及计算的量是否以统计学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，即如何采样感兴趣的事件，很少发生在可访问的时间尺度的模拟。对于许多当代重要的问题，使用传统方法计算某些感兴趣的属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，对应于势能或自由能表面上的大势垒。对这类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变。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种罕见事件问题，并将计算机模拟扩展到更大的系统和更长的时间尺度。我们建议联合收割机的两个最成功的方法，一个是基于几何优化，和其他显式动力学，产生一个混合的方法，是足够有效地处理介观问题。几何优化方法可以处理任意慢的事件，因为所讨论的障碍是直接计算的。然后，速率常数可以使用来自单分子速率理论的众所周知的工具来评估，该理论涉及一系列近似。通过结合明确的动力学的几何优化确定的途径，我们的目标是产生更准确的速率常数和扩展域模拟治疗更复杂的systems.Two重要的应用程序将被考虑。首先，我们将分析各种各样的散装系统，包括模型，形成玻璃，液晶和颗粒状材料的成核途径。我们最雄心勃勃的目标是利用这些知识来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将立即对制药公司和基于玻璃或液晶的材料的制造有用。描述和预测玻璃质材料的老化特性的能力将立即得到许多重要的应用，我们要考虑的第二个应用涉及从介观构件设计分子马达。在这里，我们将寻求确定控制化学能转化为可用功的效率的一般设计原则。因此，我们将指导实验中的分子成分的选择，以产生一个有效的马达，包括由形状，电荷等控制的分子间相互作用的特性。

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.