Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas

Area of Science:

• Plasma Physics
• Materials Science
• Computational Chemistry

Background:

• Understanding plasma phase behavior is crucial for astrophysics and materials science.
• Previous models for carbon-oxygen and oxygen-selenium plasmas exist but require validation through advanced simulation techniques.

Purpose of the Study:

• To determine the liquid-solid phase diagram for carbon-oxygen and oxygen-selenium plasma mixtures.
• To investigate the influence of finite-size and nonequilibrium effects on phase behavior.
• To provide accurate phase diagrams for astrophysical and materials science applications.

Main Methods:

• Utilized two-phase molecular dynamics simulations with large ion counts (27,648 and 55,296).
• Employed a bond angle metric to distinguish liquid, solid, and interface regions.
• Calculated diffusion constants to monitor nonequilibrium effects and assess ion mobility.

Main Results:

• The carbon-oxygen phase diagram shows excellent agreement with existing predictions, indicating minimal finite-size and nonequilibrium errors.
• In the carbon-oxygen solid phase, oxygen ion diffusion is significantly slower than carbon ion diffusion.
• The oxygen-selenium system exhibits remarkably fast oxygen diffusion in a selenium crystal, comparable to liquid phase diffusion, and a lower melting temperature than predicted, likely due to electron screening.

Conclusions:

• The carbon-oxygen phase diagram is now considered accurately determined.
• The oxygen-selenium system serves as a valuable model for nucleosynthesis ash, with its unique diffusion properties and melting point influenced by electron screening.