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The decomposition of dodecahedron and tetrakaidecahedron in methane hydrate is studied by molecular dynamics simulation. For each single cage‐like structure, the decomposition is divided into three stages according to the different characteristics in each stage. The interaction from each part of the system to the single cage‐like structure is analyzed. The feature of hydrogen bond and the transformation in vibration density of states of oxygen during decomposition are investigated. The influences of heat flow disturbance and different initial temperature are estimated. The results show that for two different size structures, the time required by each stage is different. However, the percentage of residual hydrogen bond basically keeps the same. When decomposing, the total interaction energy to the cage‐like structure increases and the vibration density of states of oxygen in cage‐like structure converts more similar to that in liquid water. It suggests that heat flow disturbances and higher initial temperature may exacerbate the decomposition of single cage‐like structure.

Herein, several molecular systems are simulated by molecular dynamics to study the decomposition process and fluctuation−dissipation characteristics of spherical methane hydrates under different conditions. The spherical radius and the movement of the hydrate−liquid water interface during decomposition are measured. Different fitted formulas of the variation of methane numbers are obtained from the decomposition of spherical and bulk methane hydrates. Fluctuation−dissipation characteristics for spherical methane hydrates with different radii are analyzed, which show that increasing the scale of hydrates can increase the relaxation time and slow down the fluctuation process. The variations of the hydrogen bond and hydrogen-bond lifetime are calculated. For hydrate phase water, the peak of the hydrogenbond lifetime lies between 8 and 10 ps. After complete decomposition, the hydrogen-bond lifetime mainly distributes in 0 and 2 ps and the peak disappears. The effects of temperature, cage occupancy, liquid phase environment, and spherical hydrate scale are explored. The decomposition activation energy for the spherical hydrate with a radius of 20 Å is calculated to be 52.23 kJ/mol. It can speed up the decomposition rate as well as the diffusion of methane and water molecules with a lower cage occupancy. For the effect of the liquid phase environment, it is found that the number of liquid water rarely affects the decomposition. However, when the Na + and Cl − concentrations change from 0 to 10%, the decomposition time reduces from ∼511 to ∼369 ps, which indicates that there is an obviously positive impact on decomposition.