Thermodynamical study of N$_2$ clathrate hydrate from DFT calculations

TL;DR

This study uses density functional theory to analyze the thermodynamic stability of N₂ clathrate hydrates in different structures, considering composition and pressure effects at zero Kelvin, providing a first-principles framework.

Contribution

It offers a detailed first-principles thermodynamic analysis of N₂ hydrate stability, including the effects of cage occupancy and pressure, which was not comprehensively addressed before.

Findings

revPBE-D3(0) best reproduces experimental data

sI with single occupancy stable up to ~0.8 GPa

Pressure stabilizes sII with double occupancy

Abstract

Thermodynamic stability of N$_2$ 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 B$_0$ . 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 $\sim$ 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 N$_2$ hydrate stability and a baseline for finite-temperature extension.