Water Freezing and Ice Melting.

Area of Science:

• Physical Chemistry
• Computational Materials Science
• Thermodynamics

Background:

• First-order phase transitions, such as freezing and melting, are critical phenomena in materials science.
• Accurately simulating coexisting phases and phase transitions remains a computational challenge.
• Understanding the thermodynamics of water's phase transitions is essential for various scientific disciplines.

Purpose of the Study:

• To present and validate the isobaric molecular dynamics (MD) version of the generalized replica exchange method (gREM).
• To apply gREM to the phase transitions of water, specifically freezing and melting of hexagonal and cubic ice.
• To obtain thermodynamic properties and analyze phase transition pathways.

Main Methods:

• Implementation of the isobaric molecular dynamics version of the generalized replica exchange method (gREM).
• Simulation of liquid water freezing and hexagonal/cubic ice melting processes.
• Application of entropic analysis to determine equilibrium transition temperatures, latent heats, and surface tensions.

Main Results:

• gREM successfully sampled coexisting liquid-water and ice phases.
• Hysteresis between freezing and melting processes was observed and analyzed.
• Accurate thermodynamic properties (transition temperatures, latent heats, surface tensions) were obtained for hexagonal and cubic ice transitions.
• A novel method for assigning water molecules to symmetry types was developed.
• Freezing pathways revealed intermediate layered structures composed of hexagonal and cubic ice.

Conclusions:

• The generalized replica exchange method (gREM) is a powerful tool for simulating first-order phase transitions and coexisting phases.
• The study provides accurate thermodynamic data for water's phase transitions, validating the gREM approach.
• Observed freezing pathways offer new insights into the molecular mechanisms of ice formation.