First principles centroid molecular dynamics simulation of high pressure ices

Area of Science:

• Condensed matter physics
• Materials science
• Computational chemistry

Background:

• High-pressure ices (HPIs) exhibit complex structural and phase behaviors under extreme conditions.
• Understanding the role of nuclear quantum effects (NQEs) is crucial for accurately modeling HPI properties.

Purpose of the Study:

• To investigate the impact of NQEs on the structural, elastic, electronic, and vibrational properties of HPIs VIII, VII, and X.
• To elucidate the role of NQEs in pressure-induced phase transitions of H₂O ice at 270 K.

Main Methods:

• First principles centroid molecular dynamics (CMD) simulations were employed.
• Calculations were performed at a temperature of 270 K for HPIs VIII, VII, and X.
• Internal pressure was computed under constant NVT conditions.

Main Results:

• NQEs were found to play a significant role in the pressure-induced proton order-disorder transitions (ice VIII to ice VII at ~30 GPa).
• NQEs influence the transition to the symmetric phase (ice X at ~80 GPa).
• NQEs affect the equation of state of HPIs, as evidenced by internal pressure calculations.

Conclusions:

• First principles CMD is a reliable method for reproducing experimental vibrational spectra of HPIs.
• NQEs are essential for a comprehensive understanding of HPI properties and phase transitions, even at relatively high temperatures.