Methane-water clusters under pressure: are clathrate cages optimal clusters?

Area of Science:

• Computational chemistry
• Physical chemistry
• Materials science

Background:

• Water clusters exhibit well-defined structures.
• Methane molecules can interact with water clusters.
• External pressure significantly influences molecular structures.

Purpose of the Study:

• To investigate the structural behavior of methane-water clusters (CH4(H2O)n, n=4-21) under external pressure.
• To determine the impact of pressure on the transition from pure water cluster structures.
• To identify the preferred high-pressure structures for these mixed clusters.

Main Methods:

• Global cluster structure optimization was employed.
• Simulations were performed on CH4(H2O)n clusters with varying 'n' (4-21).
• The influence of external pressure was systematically studied.

Main Results:

• A structural transition occurs in methane-water clusters under pressure, deviating from pure water cluster structures.
• High-pressure conditions favor the formation of "nestlike" structures.
• Clathratelike cages, while sometimes local minima, are less stable than nestlike structures across all studied sizes and pressures.

Conclusions:

• External pressure fundamentally alters the structure of methane-water clusters.
• "Nestlike" structures represent the stable high-pressure form for these mixed clusters.
• The transition pressure and size dependence are key factors in determining cluster morphology.