Solid-Fluid Equilibria of Atoms with Soft Repulsive and Short-Range Cohesive Interactions

Area of Science:

• Materials Science
• Thermodynamics
• Computational Physics

Background:

• Solid-fluid phase equilibria are defined by melting and freezing curves at temperatures and pressures above the triple point.
• The termination behavior of these phase boundaries under extreme conditions remains an unresolved scientific question.

Purpose of the Study:

• To investigate the nature of melting and the termination of solid-fluid phase boundaries under extreme conditions using molecular simulations.
• To determine if melting curves exhibit a critical point, a maximum, an asymptotic limit, or continue indefinitely.

Main Methods:

• Utilized molecular simulations with a soft interatomic potential to model material behavior.
• Analyzed the density changes and phase equilibria at high temperatures and pressures.

Main Results:

• Observed a negative change in volume upon melting at high pressures, a characteristic usually seen only in water.
• Provided evidence that melting and freezing curves can merge at a melting temperature maximum point.
• Identified this merging as a potential general characteristic of soft atomic fluids under extreme pressure.

Conclusions:

• The study demonstrates that melting curves can terminate in a maximum temperature point under extreme pressures.
• This behavior is linked to anomalous negative volume changes during melting in soft atomic fluids.
• The findings contribute to understanding phase transitions in materials under extreme thermodynamic conditions.