Medium-range order in amorphous ices revealed by persistent homology.

Area of Science:

• Condensed matter physics
• Materials science
• Computational chemistry

Background:

• Amorphous materials like glassy water exhibit medium-range order (MRO) despite lacking long-range crystalline structure.
• Experimental techniques like x-ray scattering show MRO signatures, but their real-space origin remains unclear.

Purpose of the Study:

• To investigate the real-space origin of MRO signatures in low-density amorphous (LDA) and high-density amorphous (HDA) ices.
• To identify and characterize MRO structures within these amorphous water systems.

Main Methods:

• Utilized molecular dynamics simulations to model LDA and HDA ices.
• Applied persistent homology (PH) to analyze the simulation data and identify topological features.
• Correlated identified MRO structures with experimental scattering data.

Main Results:

• Discovered prominent MRO ring structures in both LDA and HDA ices.
• Characterized differences in MRO rings: HDA rings are smaller, less planar, and more membered than LDA rings.
• PH-identified MRO rings accurately reproduced the position and width of experimental diffraction peaks.

Conclusions:

• Persistent homology is an effective tool for uncovering hidden MRO in amorphous systems.
• The identified MRO ring structures provide the real-space origin for experimental diffraction peaks in glassy water.
• This work advances the understanding of structural order in amorphous ices.