Tuning the Liquid-Liquid Transition by Modulating the Hydrogen-Bond Angular Flexibility in a Model for Water

Area of Science:

• Computational chemistry
• Physical chemistry
• Materials science

Background:

• The ST2 model is a well-established model for simulating water.
• Understanding the behavior of water under various conditions is crucial in many scientific fields.
• The liquid-liquid critical point in water models has been a subject of intense research.

Purpose of the Study:

• To investigate the effect of hydrogen-bond angular flexibility on the ST2 water model.
• To determine how modifying this flexibility impacts the thermodynamic stability of liquid water and ice.
• To analyze the behavior of the liquid-liquid critical point as flexibility is altered.

Main Methods:

• A simple extension of the ST2 model was developed.
• This extension allows for continuous modification of hydrogen-bond angular flexibility.
• Thermodynamic stability and critical point location were analyzed computationally.

Main Results:

• Increased hydrogen-bond flexibility shifts the liquid-liquid critical point.
• The critical point moves from the region where ice is stable to a region where liquid water is more stable.
• This modification affects the relative thermodynamic stability of liquid water and hexagonal/cubic ice.

Conclusions:

• The study confirms that the liquid-liquid transition in the ST2 model is a genuine phenomenon.
• Hydrogen-bond angular flexibility plays a critical role in the behavior of tetrahedral network-forming liquids.
• These findings have significant implications for understanding water and similar substances.