Pronounced structural crossover in water at supercritical pressures
C Cockrell1, O A Dicks1, V V Brazhkin2
1School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, United Kingdom.
Summary
Supercritical water exhibits a structural crossover across the Frenkel line at high pressures, linking its structural and dynamical properties. This transition, previously unexplored, reveals new insights into the water phase diagram.
Area of Science:
- Physical Chemistry
- Materials Science
Background:
- Extensive research exists on solid and liquid water phases.
- Deeply supercritical pressures of water remain largely unexplored.
- Properties in supercritical states are generally assumed to vary smoothly.
Purpose of the Study:
- To investigate the behavior of water at deeply supercritical pressures.
- To explore potential phase transitions or structural changes in supercritical water.
- To link structural and dynamical properties of supercritical water.
Main Methods:
- Utilizing molecular dynamics simulations.
- Analyzing pair distribution functions.
- Examining local coordination and molecular motion.
Main Results:
- Predicting a structural crossover of water across the Frenkel line at high supercritical pressures (up to 45 times the critical pressure).
- Observing changes in pair distribution functions and local coordination.
- Demonstrating a sharp crossover at low pressures, becoming smooth at high pressures.
Conclusions:
- Supercritical water undergoes a significant structural crossover across the Frenkel line.
- This crossover links the structural and dynamical properties of supercritical water.
- Provides new insights into the complex water phase diagram.
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