Atomistic-geometric simulations to investigate the mechanical stability of monocrystalline sI methane hydrates under pressure.

Gas hydrate mechanical stability under pressure is critically important in energy supply, global warming, and carbon-neutral technologies. The stability of these polyhedral guest-host crystals under increasing pressure is affected by host cage type and face connectivity as well as guest gas occupancy. The geometry-imposed cage connectivity generates crystal lattices that include inclusion-matrix material composite structures. In this paper, we integrate Density Functional Theory simulations with a polyhedral-inspired composite material model that quantifies stability limits, failure modes, and the impact of the type of cage occupancy. DFT reveals the existence of two failure mechanisms under increasing pressure: (i) a multistep lattice breakdown under total occupancy and under only large cage occupancy and (ii) a single-step breakdown under zero occupancy as well as with only small cage occupancy. The DFT-composite model predicts optimal occupancy pathways to generate strength and critical occupancy pathways to promote decomposition.