Using classical density functional theory to determine crystal-fluid surface tensions.

Area of Science:

• Condensed matter physics
• Statistical mechanics
• Computational chemistry

Background:

• Classical density functional theory (DFT) is a powerful tool for studying fluid-solid interfaces.
• Accurate calculation of surface tensions is crucial for understanding phase transitions and material properties.
• Previous models sometimes lacked accuracy or stability for complex systems.

Purpose of the Study:

• To determine fluid-solid surface tensions for hard sphere and Lennard-Jones systems using DFT.
• To validate a new, stable fundamental measure theory (FMT) model for hard spheres.
• To compare surface tensions of different crystal structures (FCC, BCC, HCP) and interfaces (solid-liquid, solid-vapor).

Main Methods:

• Utilizing classical density functional theory.
• Employing an explicitly stable fundamental measure theory (FMT) model for hard spheres.
• Performing calculations for low-index crystal faces of hard spheres and Lennard-Jones particles.
• Comparing results with existing simulation data and literature values.

Main Results:

• The stable FMT model achieves state-of-the-art accuracy for hard sphere systems.
• Calculated solid-liquid and solid-vapor surface tensions for Lennard-Jones systems show good agreement with literature.
• Body-centered cubic (BCC) crystals exhibit significantly lower solid-liquid surface tension compared to face-centered cubic (FCC) crystals.
• The BCC solid-vapor interface appears unstable, favoring a transition to the hexagonal close-packed (HCP) structure.

Conclusions:

• The employed DFT approach, particularly with the stable FMT model, provides reliable predictions for interfacial properties.
• The BCC crystal structure is less stable than FCC for solid-liquid interfaces under the studied conditions.
• The BCC phase's instability at the solid-vapor interface supports existing theoretical findings.