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论文类型：期刊论文

发表时间：2015-11-05

发表刊物：JOURNAL OF PHYSICAL CHEMISTRY A

收录刊物：SCIE、EI、PubMed、Scopus

卷号：119

期号：44

页面范围：10971-10979

ISSN号：1089-5639

摘要：In order to understand the cage fusion behavior during the nucleation processes of methane hydrate (MH), methane-encapsulated double-cage clusters (CH4)(2)(H2O) (n = 30-43) and several multicage structures with three or more cages were studied employing DFT-D methods. We find that almost all the lowest-energy double-cage structures can be constructed by merging the most stable structures of the monocage clusters CH4(H2O)n (n = 18-24). Double-cage structures can achieve higher stability through sharing a hexagon than a pentagon, which may be applicable to larger fused cage clusters. The preference of hexagons during cage fusion should be favorable for the appearance of the cages including hexagons such as the 5(12)6(2), 5(12)6(4) cages during the MH nucleation process. The symmetric C-H stretching modes of methane molecules in the double-cage structures show a clear trend of red shift with increasing size of the composing monocages. Compared with the case of monocages, the stretching frequencies of methane molecules in double-cage structures shift slightly, indicating variation of monocage configuration when cage fusion occurs. The larger multicage structures are found to possess higher fusion energies through sharing more polygons. Their thermodynamic stabilities do not simply increase with the number of fused monocages and are affected by the spatial arrangement of the building cages.