Comparing four hard-sphere approximations for the low-temperature WCA melting line.

Area of Science:

• Thermodynamics
• Computational Physics
• Materials Science

Background:

• Understanding the melting line of systems is crucial for predicting phase transitions.
• The Weeks-Chandler-Andersen (WCA) system is a fundamental model for studying fluid-solid coexistence.
• Existing hard-sphere approximations offer varying accuracy in predicting melting behavior.

Purpose of the Study:

• To accurately determine the melting-line coexistence pressure and densities for the WCA system across a wide temperature range.
• To compare the predictive capabilities of different hard-sphere approximations for the melting line.
• To derive analytical expressions for hard-sphere approximations at the zero-temperature limit.

Main Methods:

• Interface-pinning simulations were employed to capture solid-fluid interfaces.
• Numerical integration of the Clausius-Clapeyron equation was used to determine coexistence properties.
• Four hard-sphere approximations (Boltzmann, Andersen-Weeks-Chandler, Barker-Henderson, Stillinger) were evaluated.

Main Results:

• Accurate melting-line pressure and densities were obtained for the WCA system over four decades of temperature.
• The Andersen-Weeks-Chandler and Barker-Henderson theories demonstrated superior accuracy in predicting the melting line.
• Excellent agreement was observed for these theories in the zero-temperature limit.

Conclusions:

• The study provides a benchmark dataset for the WCA melting line.
• The Andersen-Weeks-Chandler and Barker-Henderson theories are recommended for accurate melting-line predictions in hard-sphere systems.
• Analytical derivations offer new insights into theoretical predictions at low temperatures.