Thermodynamic driving force for diffusion: comparison between theory and simulation.

Area of Science:

• Condensed matter physics
• Computational chemistry
• Materials science

Background:

• Lattice density functional theory (DFT) equations can be reformulated into a differential form.
• This reformulation allows for the determination of a property whose gradient is proportional to diffusive flux.
• For color counter diffusion, this property relates to the impingement rate of species onto vacancies and molecules.

Purpose of the Study:

• To investigate the relationship between the mobility of the surroundings and the diffusion flux of a species.
• To validate the finding that the impingement rate of diffusing molecules depends on the mobility of their environment.
• To determine if altering solvent mobility affects the diffusion flux of a species under controlled conditions.

Main Methods:

• Molecular dynamics (MD) simulations were employed to study color counter diffusion.
• The mobility of the solvent was systematically varied during the simulations.
• Key factors such as density gradient, available volume, and temperature were held constant.

Main Results:

• The study demonstrated that changes in solvent mobility directly influenced the flux of the diffusing species.
• This response was observed even when other critical parameters were kept invariant.
• The findings support the theoretical prediction linking diffusion flux to the mobility of the surrounding medium.

Conclusions:

• The mobility of the surrounding environment is a critical determinant of diffusion flux.
• Lattice DFT and MD simulations provide complementary insights into diffusion phenomena.
• This work highlights the importance of considering local mobility effects in diffusion modeling.