Tetrahedrality and hydrogen bonds in water

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding the structure of liquid water is crucial due to its unique properties.
• Tetrahedral coordination is a key feature in water's various phases.

Purpose of the Study:

• To investigate the tetrahedral order in liquid water across different thermodynamic conditions.
• To compare tetrahedrality with hydrogen bond counts and neighbor distributions.
• To analyze structural differences between liquid water, amorphous ice phases, and the Widom line.

Main Methods:

• Extensive molecular dynamics calculations using the BK3 model.
• Analysis of tetrahedral coordination, hydrogen bond networks, and partial pair correlation functions.
• Examination of water structure in supercooled regions, amorphous ice phases (LDA, HDA), and near the Widom line.

Main Results:

• Tetrahedrality in liquid water significantly varies with pressure, temperature, and density, unlike hydrogen bond counts.
• Lowering pressure, density, and temperature increases both the number and domain size of tetrahedral arrangements.
• Distinct differences in tetrahedrality were observed between liquid water, LDA, HDA, and across the Widom line.
• The fifth water molecule's position differs in liquid water/HDA compared to ice/LDA.

Conclusions:

• Tetrahedral order is a more sensitive indicator of water's structural changes than hydrogen bond counts.
• Thermodynamic variables profoundly influence the development of extended tetrahedral networks in water.
• The study reveals distinct structural characteristics of water in different phases and conditions, without evidence of structural heterogeneity.