A simple analytical model of water

Area of Science:

• Physical Chemistry
• Thermodynamics
• Materials Science

Background:

• Water exhibits anomalous thermal properties, including expansion upon freezing and minima in key thermodynamic variables.
• Supercooled water displays unique characteristics, such as potential first-order phase transitions and a fragile-to-strong crossover in relaxation dynamics.
• These anomalies are pressure-dependent, diminishing at elevated pressures.

Purpose of the Study:

• To present and review a recent analytical theory explaining water's anomalous thermal properties.
• To elucidate the microscopic origins of water's behavior using a simplified interaction model.
• To predict key features of water's phase diagram, including crystalline phases and fluid-fluid transitions.

Main Methods:

• Development of an analytical theory based on a simplified model of water molecule interactions.
• The model incorporates hydrogen bonds, steric repulsions, and dispersion attractions between water triplets.
• Application of the theory to predict thermal properties and phase behavior of water, particularly in the supercooled regime.

Main Results:

• The theory successfully predicts the anomalous thermal properties of water.
• It accurately forecasts the main features of water's phase diagram, including multiple crystalline phases.
• The theory also predicts a fluid-fluid transition and a fragile-to-strong crossover in supercooled liquid water.

Conclusions:

• A simplified theoretical model provides fundamental insights into the microscopic origins of water's anomalous behavior.
• The theory offers a predictive framework for understanding water's complex phase diagram and dynamic properties.
• High pressure is shown to suppress the unique anomalies observed in ambient pressure water.