Proton ordering in cubic ice and hexagonal ice; a potential new ice phase--XIc

Area of Science:

• Solid-state physics
• Materials science
• Physical chemistry

Background:

• Ordinary water ice exists in two common polytypes: hexagonal ice (Ih) and cubic ice (Ic).
• Proton ordering in ice structures significantly influences their properties and stability.
• Understanding different ice phases is crucial for various scientific disciplines.

Purpose of the Study:

• To compare the proton ordering arrangements in hexagonal ice (Ih) and cubic ice (Ic).
• To identify the most stable proton-ordered arrangement in cubic ice.
• To propose a potential new polytype of ice and discuss its preparation.

Main Methods:

• Utilizing periodic density functional theory (DFT) for electronic structure calculations.
• Employing diffusion Monte Carlo (DMC) methods for accurate energy comparisons.
• Analyzing proton ordering configurations in different ice polytypes.

Main Results:

• The most stable proton arrangement in cubic ice (Ic) was found to be isoenergetic with the proton-ordered hexagonal ice (ice XI).
• This energetically equivalent structure in cubic ice is proposed as a new polytype, designated ice XIc.
• A potential pathway for synthesizing ice XIc is discussed.

Conclusions:

• A novel, stable proton-ordered cubic ice polytype (XIc) has been identified.
• Ice XIc shares energetic equivalence with ice XI, suggesting a close relationship between these phases.
• The study opens avenues for experimental investigation and synthesis of this new ice phase.