First-principles investigation of the terahertz absorption spectrum and thermodynamic properties of methane hydrate

Methane hydrates are crystalline compounds widely found in seafloor sediments and permafrost regions, playing a significant role in energy storage and climate dynamics. The primary structural forms of methane hydrates include the s-I, s-II, and s-H phases. In this study, we systematically investigate the spectroscopic and thermodynamic properties of these three structures using first-principles calculations. By analyzing the contributions of vibrational modes (phonons), we computed and interpreted their infrared and terahertz absorption spectra, clearly distinguishing between intermolecular translational and rotational motions, as well as intramolecular vibrations. Furthermore, within the framework of the harmonic approximation, we calculated the thermodynamic properties over a temperature range of 0-100 K. The results indicate that the s-I structure exhibits greater thermodynamic stability under low-temperature conditions compared to the s-II and s-H phases. This study validates the reliability of our computational approach and provides in-depth theoretical insights into the spectral behavior and stability variations of methane hydrates, thereby providing a scientific basis for their potential applications in energy conversion technologies and environmental research.