Freezing in resonance structures for better packing: XeF2 becomes (XeF+)(F-) at large compression

Area of Science:

• Solid-state chemistry
• High-pressure physics
• Computational materials science

Background:

• Xenon difluoride (XeF2) is a compound known to exhibit interesting properties under extreme conditions.
• Previous experimental studies suggested phase transitions and metallicity in XeF2 at high pressures up to 100 GPa.

Purpose of the Study:

• To theoretically investigate the high-pressure behavior of xenon difluoride.
• To reconcile discrepancies between existing experimental data and theoretical predictions.
• To explore structural transformations and potential metallicity in XeF2 under pressure.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Structural stability was assessed using enthalpy calculations.
• Geometry optimizations were performed for various predicted high-pressure phases.

Main Results:

• The ambient I4/mmm structure of XeF2 was found to be the most stable up to 105 GPa, contradicting experimental results.
• Experimental structures showed higher enthalpies or converged to the I4/mmm phase upon optimization.
• Above 105 GPa, a transition to the Pnma phase with bent FXeF molecules was predicted.
• Further compression to 200 GPa suggested self-dissociation into [XeF]+F−.

Conclusions:

• Theoretical calculations challenge previous experimental interpretations of XeF2's high-pressure phases.
• A new high-pressure phase (Pnma) and a high-pressure ionic dissociation pathway for XeF2 are proposed.
• The findings provide a revised understanding of xenon difluoride's behavior under extreme compression.