高压下气体水合物结构及相稳定性的理论研究

气体水合物是由轻质气体和水在低温高压下生成的固体结晶物质，其结构与轻质气体分子的大小、类型、分子性质、以及所处环境条件有关。气体水合物是21世纪的理想能源，其结构及相稳定性问题是制约其应用的关键问题。本项目拟采用基于粒子群优化算法的晶体结构预测技术，结合第一性原理计算，在0-10GPa的低压范围内，研究不同压力下气体水合物M•nH2O （M=CH4，CO2，H2；n=2-6）的晶体结构及成键特点；在100-500GPa的高压范围内，探索M气体分子与H2O分子高压下的成键方式，判断是否有新的C-H-O三元或二元化合物生成。在100-300K温度范围内，通过从头算分子动力学模拟，分析搜索到的气体水合物晶体结构随着温度升高的相稳定性，以及分解条件。本项目在不同温度和压力条件下M•nH2O的结构变化规律以及相变机理研究方面，有望获得原创性成果，其研究结论将为气体水合物的应用研究提供理论上的支持。

Gas hydrates are solid crystalline materials which are comprised of light gases and water at low temperatures and high pressures. The structures depend on the size, type, properties of light gas molecules, and also are related to the environmental conditions. Though gas hydrates are ideal energy source in the 21st century, their structures and phase stabilities are key issues to constrain their applications. In this project, we will investigate the crystal structures and bonding characteristics of gas hydrate M•nH2O （M=CH4，CO2，H2；n=2-6）in the low pressure range of 0-10GPa. Meanwhile the question whether there is a new generation C-H-O ternary or binary compound in the high pressure range of 100-500GPa will be answered by investigating the bonding mode between gas molecule M and H2O in the corresponding pressure range. For this research purposes, we will adopt the crystal structure prediction technology based on the particle swarm optimization algorithm combined with the first-principle calculation. At the same time, phase stability of stable crystal structure of gas hydrate at 100-300K will be investigated by ab initio molecular dynamics simulations. The temperatures for the decompositions of stable gas hydrate will be obtained. In this project, it is very promising to obtain some original results about the structure variation rules and phase transition mechanism of M • nH2O under different temperatures and pressures. We hope the conclusions can provide theoretical supports for the application of gas hydrates.