Computer simulation of hypothetical hydrogen ordered structure of ice XIX

Area of Science:

• Materials Science
• Crystallography
• Physical Chemistry

Background:

• Ice XIX is a recently discovered hydrogen-ordered polymorph of ice VI.
• It forms a unique group with ice XV and ice VI.
• The precise crystal structure of ice XIX remains unconfirmed.

Purpose of the Study:

• To determine the exact crystal structure of ice XIX.
• To differentiate between proposed hydrogen-ordered structures of ice XIX.
• To understand the relationship between ice XIX, ice XV, and ice VI.

Main Methods:

• Utilized neutron diffraction data from Gasser et al. to construct four possible ice XIX conformations.
• Employed first-principles density functional theory for structure optimization.
• Simulated Raman scattering spectra for comparison with experimental data.

Main Results:

• Excluded a ferroelectric structure with space group Cc.
• Identified three candidate structures consistent with experimental Raman spectra.
• Two candidate structures are ferroelectric (space group P21), one is weak ferroelectric (space group Cc).

Conclusions:

• The crystal structure of ice XIX is likely a mixture of several hydrogen-ordered configurations.
• The study provides strong evidence supporting specific ferroelectric and weak ferroelectric models for ice XIX.
• Further research may refine the understanding of this unique ice polymorph.