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System size dependence of the diffusion coefficient in a simple liquid
1RICS, National Institute of Advanced Industrial Science and Technology (AIST), Central 2,1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan. m.fushiki@aist.go.jp
Summary
A new equation estimates how system size affects particle diffusion in fluids. It shows good agreement with simulations, especially for denser fluids and heavier particles.
Area of Science:
- Physics
- Physical Chemistry
Background:
- Understanding particle diffusion in fluids is crucial for various physical and chemical processes.
- Existing models often struggle to accurately predict diffusion coefficients across different system sizes and densities.
Purpose of the Study:
- To develop and validate an equation for estimating the system size dependence of the self-diffusion coefficient of a tagged particle in a simple fluid.
- To compare theoretical predictions with molecular dynamics simulations.
Main Methods:
- Utilizing linear-response theory and linearized hydrodynamics to derive the diffusion equation.
- Performing molecular dynamics simulations on a hard-sphere fluid at two densities (rhosigma³ ≈ 0.88 and 0.47).
Main Results:
- The equation provides good agreement with simulations at higher fluid densities.
- Agreement improves at lower densities when considering the tagged particle's diffusion effect.
- The equation accurately predicts the diffusion coefficient for infinite systems, matching long-time tail contributions.
Conclusions:
- The developed equation is a reliable tool for estimating particle diffusion coefficients, particularly in denser fluids.
- The model's accuracy is enhanced by accounting for specific particle properties, such as mass relative to the fluid.
- The findings validate the theoretical approach through molecular dynamics calculations.