Abstract Molecular dynamics simulation is used to study the dissociation behavior of methane hydrate with different composition in a three-phase coexistence of liquid water + hydrate + methane gas. Five hydrate systems with various cage emptiness capacity and composition distribution are built and studied. In hydrate system with empty cages, an abnormal dash response occurred in the dissociation process compared to a stepwise respond observed in the fully occupied system. The effect of large/small cage-specific occupancy is considered in this simulation with energy evolution used to describe the dissociation rate. Hydrates with similar occupancy differ in dissociation behavior depending on the type of empty cages (small or large). Hydrate system with empty small cages show higher stability than system with larger empty cages. Ab initio calculation is used to explain this phenomenon, stability decrease of large cages loss of guest molecule is found to be higher than small cages from the calculation of stabilization energy. The differences in cage-specific occupancy effect between CO2 and CH4 hydrate is also discussed to compared with perivous researches. It has been found that the presence of CO2 molecules in small cages has less influence in stability compared to CH4 molecules. As for the stability of large cages, the existence of CO2 molecule and CH4 molecule has a similar contribution.

中文翻译：

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笼具特定占有率对三相共存甲烷水合物体系解离速率的影响：分子动力学模拟研究

摘要 利用分子动力学模拟研究了液态水+水合物+甲烷气三相共存下不同成分甲烷水合物的解离行为。建立并研究了具有不同笼子空容量和成分分布的五个水合物系统。在具有空笼子的水合物系统中，与在完全占据系统中观察到的逐步响应相比，在解离过程中发生了异常的冲刺响应。在这个模拟中考虑了大/小笼特定占用的影响，能量演化用于描述解离率。根据空笼的类型（小或大），具有相似占有率的水合物在解离行为上有所不同。具有空小笼子的水合物系统比具有更大空笼子的系统显示出更高的稳定性。用从头算计算来解释这一现象，从稳定能的计算发现客体分子大笼损失的稳定性下降高于小笼。还讨论了 CO2 和 CH4 水合物在笼具特定占用效应方面的差异，并与以往研究进行了比较。已经发现，与 CH4 分子相比，小笼中 CO2 分子的存在对稳定性的影响较小。对于大笼子的稳定性，CO2分子和CH4分子的存在有相似的贡献。还讨论了 CO2 和 CH4 水合物在笼子特定占用效应上的差异，并与现有研究进行了比较。已经发现，与 CH4 分子相比，小笼中 CO2 分子的存在对稳定性的影响较小。对于大笼子的稳定性，CO2分子和CH4分子的存在有相似的贡献。还讨论了 CO2 和 CH4 水合物在笼具特定占用效应方面的差异，并与以往研究进行了比较。已经发现，与 CH4 分子相比，小笼中 CO2 分子的存在对稳定性的影响较小。对于大笼子的稳定性，CO2分子和CH4分子的存在有相似的贡献。