A Reverse Nonequilibrium Molecular Dynamics Algorithm for Coupled Mass and Heat Transport in Mixtures

Area of Science:

• Computational chemistry
• Materials science
• Statistical mechanics

Background:

• Molecular dynamics (MD) simulations are crucial for understanding material properties at the molecular level.
• Previous methods like reverse nonequilibrium molecular dynamics (RNEMD) effectively simulated temperature and velocity gradients.
• However, simulating concentration gradients in mixtures using MD has remained a challenge.

Purpose of the Study:

• To introduce a novel method for generating stable nonequilibrium concentration gradients in molecular mixtures.
• To extend existing RNEMD techniques to address particle flux simulations.
• To accurately determine transport properties, including diffusion coefficients and activation energies.

Main Methods:

• Developed the scaled particle flux-reverse nonequilibrium molecular dynamics (SPF-RNEMD) algorithm.
• Simultaneously computed energies and forces for molecules in distinct simulation box regions.
• Employed a particle scaling variable to drive molecule migration and establish particle flux.

Main Results:

• Successfully generated concentration gradients in mixtures of identical and Lennard-Jones particles.
• Obtained Fick diffusion constants for various mixtures.
• Demonstrated the calculation of temperature-dependent diffusion coefficients and activation energies.
• Computed the diffusive permeability of a molecular fluid through a graphene membrane.

Conclusions:

• The SPF-RNEMD method provides a robust approach for simulating nonequilibrium concentration gradients in molecular systems.
• This technique facilitates the accurate determination of diffusion coefficients and coupled transport properties.
• The method is applicable to bulk mixtures and interfacial systems, such as fluid transport through nanoporous membranes.