Modeling fluid diffusion using the lattice density functional theory approach: counterdiffusion in an external field.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Diffusivity dependence on temperature, pressure, and composition is poorly understood.
• Molecular-level understanding of diffusion, especially in gases, requires complex simulations.
• Existing rigorous methods for diffusion modeling are computationally demanding.

Purpose of the Study:

• To develop a computationally tractable Lattice Density Functional Theory (LDFT) for modeling diffusion.
• To supplement existing, rigorous but computationally expensive diffusion modeling methods.
• To present and demonstrate the LDFT approach using a specific diffusion problem.

Main Methods:

• Developed a Lattice Density Functional Theory (LDFT) approach.
• Extended Equilibrium LDFT for adsorption and phase behavior to model diffusion.
• Applied LDFT to model color counterdiffusion in an external potential field.

Main Results:

• The LDFT approach successfully modeled diffusion with density profile oscillations.
• Oscillations were attributed to nearest-neighbor and next nearest-neighbor interactions.
• LDFT showed qualitative and quantitative agreement with Grand Canonical Molecular Dynamics simulations.

Conclusions:

• LDFT provides a valuable, computationally efficient method for diffusion modeling.
• The approach accurately accounts for molecular interactions, similar to van der Waals theory.
• LDFT successfully describes complex diffusion phenomena, including density profile oscillations.