Thermodynamic Study of N ₂ Clathrate Hydrates from DFT Calculations

Thermodynamic stability of N2 clathrate hydrates in the sI and sII structures is investigated using density functional theory with several exchange–correlation functionals, explicitly accounting for composition (cage occupancies) and pressure at T = 0 K. Among the tested functionals, revPBE-D3(0) best reproduces experimental lattice parameters and bulk moduli B0. Energetic analyses confirm the strong impact of large-cage double occupancy on sI, whereas the convex-hull results show that sI with single occupancy remains thermodynamically stable up to ∼0.8 GPa alongside sII with single occupancy. Increasing pressure then stabilizes sII with double occupancy, consistent with its larger large-cage volume and lower framework strain. These results provide a coherent, first-principles thermodynamic framework for N2 hydrate stability and a baseline for finite-temperature extension.