Effects of ensembles on methane hydrate nucleation kinetics

By performing molecular dynamics simulations to form a hydrate with a methane nano-bubble in liquid water at 250 K and 50 MPa, we report how different ensembles, such as the NPT, NVT, and NVE ensembles, affect the nucleation kinetics of the methane hydrate. The nucleation trajectories are monitored...

Full description

Bibliographic Details
Published in:Physical Chemistry Chemical Physics
Main Authors: Zhang, Zhengcai, Liu, Chan-Juan, Walsh, Matthew R., Guo, Guang-Jun
Format: Article in Journal/Newspaper
Language:English
Published: 2016
Subjects:
Science & Technology
Physical Sciences
Chemistry
Physics
MOLECULAR-DYNAMICS SIMULATIONS
HOMOGENEOUS CRYSTAL NUCLEATION
GAS HYDRATE
AQUEOUS METHANE
LIQUID WATER
GROWTH
MECHANISMS
SIZE
CRYSTALLIZATION
SOLUBILITY
Physical
Atomic
Molecular & Chemical
Methane hydrate
Online Access:http://ir.giec.ac.cn/handle/344007/11774
https://doi.org/10.1039/c6cp02171a
Description
Summary:By performing molecular dynamics simulations to form a hydrate with a methane nano-bubble in liquid water at 250 K and 50 MPa, we report how different ensembles, such as the NPT, NVT, and NVE ensembles, affect the nucleation kinetics of the methane hydrate. The nucleation trajectories are monitored using the face-saturated incomplete cage analysis (FSICA) and the mutually coordinated guest (MCG) order parameter (OP). The nucleation rate and the critical nucleus are obtained using the mean first-passage time (MFPT) method based on the FS cages and the MCG-1 OPs, respectively. The fitting results of MFPT show that hydrate nucleation and growth are coupled together, consistent with the cage adsorption hypothesis which emphasizes that the cage adsorption of methane is a mechanism for both hydrate nucleation and growth. For the three different ensembles, the hydrate nucleation rate is quantitatively ordered as follows: NPT > NVT > NVE, while the sequence of hydrate crystallinity is exactly reversed. However, the largest size of the critical nucleus appears in the NVT ensemble, rather than in the NVE ensemble. These results are helpful for choosing a suitable ensemble when to study hydrate formation via computer simulations, and emphasize the importance of the order degree of the critical nucleus.

Similar Items