From soft- to hard-sphere fluids: Crossover evidenced by high-frequency elastic moduli

Area of Science:

• Physics
• Materials Science
• Computational Chemistry

Background:

• Conventional Zwanzig-Mountain expressions for elastic moduli diverge at the hard-sphere (HS) limit.
• True hard-sphere fluids exhibit finite elastic moduli, creating a theoretical paradox.

Purpose of the Study:

• Resolve the paradox of diverging moduli in hard-sphere fluid models.
• Identify the soft-to-hard-sphere crossover in fluid thermodynamics and excitations.
• Develop accurate models for hard-sphere fluid elasticity.

Main Methods:

• Extensive in silico studies of fluids with repulsive power-law interactions (∝r^{-n}).
• Analysis of fluid excitations and thermodynamics.
• Model development for the hard-sphere regime.

Main Results:

• Located the soft-to-hard-sphere crossover at repulsive exponents n≃10-20.
• Demonstrated that this crossover explains the finite elastic moduli of hard-sphere fluids.
• Developed a simple and accurate model for hard-sphere fluid elasticity.

Conclusions:

• The soft-to-hard-sphere crossover is crucial for understanding fluid elasticity.
• The developed model accurately describes hard-sphere fluid behavior.
• Findings have implications for diverse systems including simple fluids, melts, and glasses.