Disorder-dominated and scattering-dominated thermal transport in clathrate hydrates

Abstract

Methane hydrate (MH) is an ice-like compound where methane molecules are encased within a lattice of water molecules. Found abundantly on ocean floors, MHs can influence future methane supplies, ocean floor stability, and climate change. In this study, a high-precision deep neural network interatomic potential for MHs is developed using ab initio molecular dynamics. Our findings reveal a transition between disorder-dominated and scattering-dominated lattice thermal transport in partially filled MHs, which are the most common form in real-world conditions. Although guest methane molecules have a minimal effect on the anharmonicity of the host lattice and the phonon band structure, they significantly increase the scattering rate of host lattice phonons by enlarging their anharmonic scattering phase space. Spectral phonon analysis further shows that methane guest molecules scatter low-frequency phonons associated with water molecule vibrations, considerably reducing the thermal conductivity of filled MHs.