Molecular Modeling of Nucleation and Growth of Clathrate Hydrates

犹他大学的Valeria Molinero获得了化学部门化学结构、动力学和方法项目的一项计算研究的资助，该研究旨在阐明笼形水合物从水溶液和冰中成核和生长的微观途径。该项目将先进的模拟方法与原子和粗粒度分子动力学模拟相结合，对罕见的成核事件进行采样。该项目测试了一个变革性的假设：水的单原子模型具有非常短程的相互作用，没有氢原子，但能够形成典型的四面体？与完全原子化的水模型相比，水的“氢键”构型产生包合物的成核和生长遵循相同的途径。如果这种方法得到验证，它将允许以不到1%的计算成本研究分子机制。该研究首次确定了含有大客体和亲水客体以及两个不同客体（双客体）的包合物的分子形成机制和核结构。这是第一个利用模拟研究冰包合物成核和生长机制以及冰/包合物和冰/客体界面结构的项目。包合物水合物作为一种丰富的能源，在天然气和氢气的储存和运输以及二氧化碳的封存方面有着很高的前景。这些应用面临的一个突出挑战是气体水合物包合物形成的缓慢动力学。另一方面，包合物堵塞会在油气管道中形成，造成巨大的经济损失和安全隐患。阻碍或加速包合物结晶的关键障碍是缺乏对包合物成核和生长的分子机制的理解。参与这个项目的有一位本科院校威斯敏斯特学院的教授，以及本科生和研究生。PI和她的研究小组还参加了犹他州科学中心的一个名为“车轮上的狮子座”的高中推广项目。

Valeria Molinero of the University of Utah is supported by an award from the Chemical Structures, Dynamics and Methods program in the Chemistry Division for a computational study aimed at elucidating microscopic pathways by which clathrate hydrates nucleate and grow from aqueous solutions and from ice. The project combines the power of advanced simulation methods to sample rare nucleation events with atomistic and coarse-grained molecular dynamics simulations. The project tests a transformative hypothesis: that a monatomic model of water with very short-ranged interactions and without hydrogen atoms but able to form the characteristic tetrahedral ?hydrogen-bonded" configurations of water, produces nucleation and grow of clathrates following the same pathways than fully atomistic water models. If this method is validated, it will permit the study of molecular mechanisms at less than 1% of the computational cost. The study is the first to determine the molecular mechanisms of formation and structure of the nuclei for clathrates containing large guest and hydrophilic guests and two distinct guests (double clathrates). It is the first project to investigate the mechanisms of nucleation and growth of clathrates from ice and the structures of the ice/clathrate and ice/guest interfaces using simulations.Clathrate hydrates hold high promise as an abundant energy source, for storage and transportation of natural gas and hydrogen, and for sequestration of carbon dioxide. A prominent challenge for these applications is the slow kinetics of formation of gas hydrate clathrates. On the other hand, clathrate plugs form in oil and gas pipelines, causing enormous economic losses and safety concerns. A key impediment to retard or hasten the crystallization of clathrates is the lack of understanding of the molecular mechanisms by which they nucleate and grow. A professor from Westminster College, an undergraduate institution, is participating in this project, as well as undergraduates and graduate students. The PI and her research group also participate in an outreach program to high schools called "The Leo on Wheels" of the Utah Science Center.