New free energy density functional and application to core-softened fluid

Area of Science:

• Physical Chemistry
• Statistical Mechanics
• Computational Physics

Background:

• Traditional density functional theories often divide potentials into hard-sphere and tail contributions.
• Existing models may require complex inputs like equations of state or excess Helmholtz free energy.
• These methods can be computationally intensive and involve adjustable parameters.

Purpose of the Study:

• To develop a new, computationally modest free energy density functional for potentials with singular repulsive cores.
• To create a functional that bypasses the need for potential division or weighted density approximations.
• To provide a self-consistent and parameter-free approach for fluid system analysis.

Main Methods:

• Developed a free energy density functional for non-hard sphere potentials.
• Utilized numerical solutions of the bulk Ornstein-Zernike integral equation theory (OZ IET).
• Determined effective hard sphere diameter self-consistently and analytically.

Main Results:

• The new functional does not require potential division or weighted density approximations.
• Input information is derived solely from OZ IET, including the second-order direct correlation function (DCF).
• Applied to core-softened fluids, it yields density distributions more consistent with simulation data than previous theories.

Conclusions:

• The proposed functional offers a computationally efficient and accurate method for studying fluids with repulsive cores.
• It successfully predicts density distributions in subcritical regions without adjustable parameters.
• Represents an advancement over existing perturbation density functional theories.