4. CNOCLUSION
In this paper, we have presented the DFT calculations of the structures and the second -order elastic parameters for NH3, N2O and NO hydrates. Taking into account the difference of the calculation method, and experimental conditions, the calculated mechanical properties of NH3, N2O and NO hydrate are analyzed. Although the mechanical properties of NH3, N2O and NO hydrates are similar, they are significantly different from those of CH4hydrate due to the polar nature of these three molecules. The current investigation is expected to further enrich the theory for hydrates and may trigger more theoretical exploration on the physics of hydrates.