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Quantum tunnelling in water clusters

水团簇中的量子隧道效应

基本信息

批准号：
EP/L010518/1
负责人：
Stuart Althorpe
金额：
$ 50.63万
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：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FL010518%2F1
关键词：
Quantum tunnelling water clusters

项目摘要

Many areas of computational chemistry and biology require accurate and computationally efficient potential energy surfaces to describe the interactions between water molecules. A great deal of progress has been made in developing and modelling such potentials, but much remains to be understood. The contemporary importance of this field is evident from new activity generated by recent experiments, and the opportunity afforded by novel instanton theory for quantum dynamics calculations suggests that rapid progress will now be possible. The study of water clusters is in principle a very powerful technique for developing and refining water potentials. Although the dynamics of such clusters may be far from that of water in the bulk, the interactions between the water molecules are of course the same, and the advantage of studying water clusters is that they are prepared at very low temperatures in a molecular beam, thus allowing precise and detailed spectroscopic measurements to be made, which respond sensitively to the properties of the water potential. If one can develop a method for computing these spectral lines from the potentials, then one has established a powerful, direct, link between the water potential and experiment. Developing such a method, and applying it to clusters containing from 4 to at least 20 water molecules is the primary goal of this proposed research. The particular transitions that we will study are those that involve quantum tunnelling between different permutational isomers of the water clusters. This analysis will allow us to use a novel 'instanton' method, which is a systematic way of obtaining a good approximation to the dominant tunnelling paths. This method has already been tested on water dimer and trimer, and shown to give excellent results that reproduce experiment. The proposed research will augment and develop further these techniques, permitting them to be applied to clusters containing up to around 20 water molecules. This work will result in the first predictions of the tunnelling splitting patterns for these clusters, which will then be compared with experimental measurements made in the group of project partner Rich Saykally (Berkeley, USA). These comparisons will then allow us to improve and refine the water potential energy surface, which will be conducted in collaboration with project partner Joel Bowman (Emory, USA).In addition to water clusters, we will also study complexes of water with hydrocarbons. This work will result in better potential energy surfaces for describing the interactions in gas hydrates, which will lead to more reliable simulations of these systems and new results that will be relevant to studies of global warming and exploitation of alternative energy reserves. An oil consultancy software company (InfoChem) is very interested in possible developments resulting from this work, and is named as one of our project partners. High resolution spectra for hydrocarbon complexes such as water-methane have already been obtained in the Saykally group, and our calculations will be carried forward with ongoing feedback from experiment.The improvements to the water potentials that result from this work are likely to lead to more reliable simulations of water in all its phases, and thus to lead to better representations and understanding of the vast range of important chemical and biological systems that contain water.

计算化学和生物学的许多领域需要准确且计算高效的势能表面来描述水分子之间的相互作用。在开发和模拟这种潜力方面已经取得了很大进展，但还有很多事情有待理解。从最近的实验产生的新活动可以明显看出该领域在当代的重要性，而新颖的瞬子理论为量子动力学计算提供的机会表明，现在有可能取得快速进展。原则上，水团簇的研究是开发和提炼水势的一种非常强大的技术。尽管这种团簇的动力学可能与整体水的动力学相去甚远，但水分子之间的相互作用当然是相同的，研究水团簇的优点是它们是在非常低的温度下在分子束中制备的，从而可以进行精确和详细的光谱测量，从而对水势的特性做出敏感的响应。如果人们能够开发出一种从势能计算这些谱线的方法，那么人们就在水势和实验之间建立了强大的、直接的联系。开发这样的方法，并将其应用于包含 4 到至少 20 个水分子的簇是这项研究的主要目标。我们将研究的特定跃迁涉及水簇不同排列异构体之间的量子隧道效应。这种分析将使我们能够使用一种新颖的“即时”方法，这是一种获得对主要隧道路径的良好近似的系统方法。该方法已经在水二聚体和三聚体上进行了测试，并显示出可重现实验的优异结果。拟议的研究将进一步增强和发展这些技术，使其能够应用于含有最多 20 个水分子的簇。这项工作将首次预测这些星团的隧道分裂模式，然后将其与项目合作伙伴 Rich Saykally（美国伯克利）小组的实验测量结果进行比较。这些比较将使我们能够改进和细化水势能面，这将与项目合作伙伴 Joel Bowman（美国埃默里大学）合作进行。除了水簇之外，我们还将研究水与碳氢化合物的复合物。这项工作将产生更好的势能表面来描述天然气水合物中的相互作用，这将导致对这些系统的更可靠的模拟以及与全球变暖和替代能源储备的开发相关的新结果。一家石油咨询软件公司 (InfoChem) 对这项工作可能产生的发展非常感兴趣，并被指定为我们的项目合作伙伴之一。 Saykally小组已经获得了水-甲烷等碳氢化合物的高分辨率光谱，我们的计算将根据实验的持续反馈进行。这项工作对水势的改进可能会导致对水的所有相进行更可靠的模拟，从而更好地表示和理解大量含有水的重要化学和生物系统。