Finite-Size Effects of Binary Mutual Diffusion Coefficients from Molecular Dynamics.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Maxwell-Stefan diffusion coefficients are critical for understanding mass transport in mixtures.
• Finite-size effects in molecular dynamics simulations can lead to inaccurate diffusivity predictions.
• Accurate diffusion coefficients are essential for designing chemical processes and materials.

Purpose of the Study:

• To investigate and quantify the finite-size effects on Maxwell-Stefan diffusion coefficients.
• To develop and validate a correction method for extrapolating finite-size diffusion coefficients to the thermodynamic limit.
• To assess the reliability of molecular dynamics simulations for predicting diffusion in various binary mixtures.

Main Methods:

• Performing molecular dynamics simulations for diverse binary Lennard-Jones systems and molecular mixtures.
• Analyzing the dependency of computed diffusivities on system size (number of molecules).
• Proposing and applying a correction formula based on system viscosity, box size, and thermodynamic factor.

Main Results:

• Observed a strong dependency of computed diffusivities on system size, with values increasing with molecule count.
• Found significant deviations between finite-size and thermodynamic limit diffusivities, especially for mixtures near demixing.
• Demonstrated that the proposed correction is crucial for accurate diffusion coefficient predictions, particularly in nonideal mixtures.

Conclusions:

• Finite-size effects are crucial and must be accounted for in molecular dynamics simulations of diffusion.
• The proposed correction method allows for reliable extrapolation of Maxwell-Stefan diffusion coefficients to the thermodynamic limit.
• Accurate prediction of diffusion coefficients is vital for understanding and engineering complex molecular systems.