Compressive behavior and electronic properties of ammonia ice: a first-principles study

Area of Science:

• Materials Science
• Planetary Science
• Quantum Chemistry

Background:

• Ammonia ice is crucial for understanding planetary formation and the origin of life.
• Previous studies identified six stable crystal structures of ammonia ice under varying pressures.

Purpose of the Study:

• To investigate the pressure-induced structural and electronic behavior of ammonia ice.
• To analyze the transition from molecular to ionic phases in ammonia ice.

Main Methods:

• Density functional theory (DFT) calculations were employed.
• Analysis included Mulliken population and electron density of states.

Main Results:

• A transition from the molecular phase (P212121) to the ionic phase (Pma2) was observed, driven by H-N bonds.
• Charge transfer between N and H atoms decreased, while bonding and charge overlap between NH3 molecules (or NH2- and NH4+ groups) increased with pressure.
• The band gap of ammonia ice exhibited a complex pressure-dependent behavior, increasing initially then decreasing.

Conclusions:

• The study elucidates the structural and electronic transformations of ammonia ice under compression.
• Findings provide valuable insights into high-pressure ammonia ice behavior relevant to planetary science.