title: Structures, Stabilities, and Spectra Properties of Fused CH4 Endohedral Water Cage (CH4)m(H2O)n Clusters from DFT-D Methods.
abstract: 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 (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.
authors.affiliation: School of Science, Dalian Nationalities University , Dalian 116600, China.
authors.forename: Lingli
authors.initials: L
authors.lastname: Tang
authors.affiliation: College of Advanced Science and Technology, Dalian University of Technology , Dalian 116024, China.|Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education , Dalian 116024, China.
authors.forename: Ruili
authors.initials: R
authors.lastname: Shi
authors.affiliation: College of Advanced Science and Technology, Dalian University of Technology , Dalian 116024, China.|Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education , Dalian 116024, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Su
authors.affiliation: College of Advanced Science and Technology, Dalian University of Technology , Dalian 116024, China.|Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education , Dalian 116024, China.|Beijing Computational Science Research Center, Beijing 100089, China.
authors.forename: Jijun
authors.initials: J
authors.lastname: Zhao