CDI-Type II: From Simulation Data to Mechanistic Understanding: Applications to Clathrate Hydrate Nucleation Mechanisms

科罗拉多矿业学院(CSM)的Amadeu Sum和David Wu、CSM和国家可再生能源实验室(NREL)的Gregg Beckham、加州大学圣巴巴拉分校的Baron Peters和犹他大学的Valeria Molineo获得了CDI第二类奖项的支持，以开发基于统计力学和信息论的新颖路径抽样方法，以便收集和分析大规模分子模拟的数据。这些新技术正在开发中，最终目的是阐明笼状水合物的成核机理。其具体目标是：1)发展有序参数来识别冰和笼状水合物的结构；2)发展分组演化路径抽样(PEPS)方法；以及3)将PEPS应用于更简单的系统，以展示该方法的实用性。序参数是这项工作的关键组成部分，因为它们提供了物理洞察力并量化了成核机制。新的采样方法(PEPS)提供了一种更有效的方法来采样和提取成核过程的机理细节，方法是沿着“反应坐标”采集演化过程。Lennard-Jones液-固成核和水-冰成核是演示这些方法的第一次应用的测试系统，然后将被应用于笼状水合物的成核。然而，这些方法本身通常是并且可以用来从各种复杂现象的分子模拟中获得理解。理解真实系统中的转变机制对于分子模拟来说是一个令人望而生畏的问题，无论是在有效的数据收集和分析方面。需要变革性的新方法，这些方法可以应用于现实系统和海量数据集，这些系统和数据集现在随着计算能力的增加而变得司空见惯。可以应用新的路径采样方法的一个特定的激励问题是笼状水合物成核的机理。笼状水合物是由甲烷或二氧化碳等非极性小分子周围的氢键水笼形成的冰状化合物，因其在能源(海底水合物的存在数量估计至少是已知石油和天然气储量的两倍)和环境(碳固存和天然水合物矿床释放甲烷)方面的重要性而引起人们的兴趣；相反，天然气水合物形成堵塞管道，对石油和天然气工业构成主要的流动保证问题，并在遏制深水石油/天然气井喷方面造成阻力。在应用于水合物成核的更广泛的背景下，将在成核理论、从疏水和亲水相互作用产生的理解以及结构量化的新方法方面获得基本知识。对水合物成核的分子机制的洞察可能具有变革性，因为它将构建从微观相互作用到宏观行为的知识，而不是目前以相反的方式为主的方法。

Amadeu Sum and David Wu, Colorado School of Mines (CSM), Gregg Beckham, CSM and National Renewable Energy Laboratory (NREL), Baron Peters , University of California, Santa Barbara and Valeria Molinero, University of Utah are supported by a CDI-TYPE II award to develop novel path sampling methods, based in statistical mechanics and information theory in order to collect and analyze data from large scale molecular simulations. These new techniques are being developed with the ultimate goal of elucidating the mechanism of clathrate hydrate nucleation. The specific aims are 1) to develop order parameters to identify ice and clathrate hydrate structures; 2) develop the Packet Evolution Path Sampling (PEPS) method; and 3) apply PEPS to simpler systems to demonstrate the utility of the method. The order parameters are a key component this effort as they provide physical insight and quantify the mechanisms of nucleation. The new sampling method (PEPS) provides a more efficient method of sampling and extracting mechanistic details on nucleation by harvesting the evolution along a 'reaction coordinate.' Lennard-Jones liquid-to-solid nucleation and water-to-ice nucleation are the testing systems to demonstrate the first application of the methods which will then be applied to clathrate hydrates nucleation. The methods themselves, however, are generally and may be used to gain understanding from molecular simulations of a variety of complex phenomena.Understanding transition mechanisms in real systems is a daunting problem for molecular simulation, both in terms of efficient data collection and analysis. There is a need for transformative new methods that can be applied to realistic systems and huge data sets that are now commonplace with increasing computing power. One specific motivating problem where new path sampling methods can be applied is to the mechanism of clathrate hydrate nucleation. Clathrate hydrates, ice-like compounds formed from hydrogen-bonded water cages surrounding small non-polar molecules such as methane or carbon dioxide, have gained interest for their importance in energy (hydrates are present at the ocean floor in quantities estimated to be at least twice that of known oil and gas reserves; conversely, plugging of pipelines by gas hydrate formation poses the primary flow assurance problem to the oil and gas industry, as well as an impedance in the containment of a deepwater oil/gas blowout) and the environment (carbon sequestration and methane release from natural hydrate deposits). In a broader context for the application to hydrate nucleation, fundamental knowledge will be gained in nucleation theory, understanding arising from hydrophobic and hydrophilic interactions, and new approaches for structural quantification. Insight into the molecular mechanism for hydrate nucleation may be transformative because it will be constructing knowledge from microscopic interactions to macroscopic behavior, as opposed to current approaches where the reverse is predominant.