Simulating the phosphorus fluid-liquid phase transition up to the critical point

Area of Science:

• Computational materials science
• Physical chemistry
• Condensed matter physics

Background:

• Phosphorus exhibits complex phase behavior, including transitions between molecular and network liquid states.
• Understanding these transitions is crucial for predicting material properties under extreme conditions.

Purpose of the Study:

• To investigate the temperature dependence of the fluid-liquid phase transition in phosphorus.
• To elucidate the structural transformation from a molecular fluid to a network liquid.
• To identify critical phenomena and triggering mechanisms for the phase transition.

Main Methods:

• Car-Parrinello molecular dynamics simulations.
• Density-functional theory (DFT) with B-LYP gradient-corrected functional.
• Simulations performed in a constant pressure ensemble over a temperature range of 2500–3500 K.

Main Results:

• Increasing temperature causes the molecular P4 fluid to network liquid transition to occur at lower pressures.
• The transition involves a density increase, which diminishes with rising temperature and disappears at 3500 K.
• Signals of near- and super-criticality were observed between 3100–3500 K.
• Local structural changes were identified as triggers for the overall transition.

Conclusions:

• The study provides a detailed atomistic understanding of phosphorus phase transitions under varying temperature and pressure.
• Findings are consistent with experimental observations and offer insights into phosphorus' behavior near critical points.
• Identified local structural changes offer potential avenues for controlling phosphorus' phase behavior.