Rotational and translational diffusion of liquid n-hexane: EFP-based molecular dynamics analysis

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding molecular diffusion is crucial for predicting liquid properties and reaction dynamics.
• Traditional hydrodynamic models offer a simplified view of diffusion, often neglecting molecular-specific interactions.

Purpose of the Study:

• To comprehensively assess translational and rotational diffusion in liquid n-hexane using advanced simulation methods.
• To analyze the coupling between different degrees of freedom in molecular diffusion.
• To compare simulation results with predictions from hydrodynamic theories.

Main Methods:

• Utilized Molecular Dynamics (MD) simulations with the Effective Fragment Potential (EFP) method.
• Decomposed translational diffusion into components parallel and perpendicular to the molecular axis.
• Analyzed rotational diffusion into tumbling and spinning motions.
• Calculated four diffusion coefficients and related them to the diffusion tensor.

Main Results:

• Provided a detailed characterization of diffusion in liquid n-hexane.
• Demonstrated that coupling between translational and rotational degrees of freedom is minimal for a body-fixed molecular frame.
• Hydrodynamic analysis supported the EFP MD findings regarding the diffusion tensor.
• Identified limitations of the hydrodynamic treatment, especially for rotational diffusion in neat liquids.

Conclusions:

• EFP MD simulations offer a robust method for detailed molecular diffusion analysis.
• Hydrodynamic models provide a useful but incomplete picture of diffusion in neat liquids.
• The study highlights the importance of molecular-level simulations for accurate diffusion characterization.