Self-consistent molecular dynamics calculation of diffusion in higher n-alkanes

Area of Science:

• Computational chemistry and physics
• Materials science and simulation

Background:

• Diffusion coefficient calculations are crucial in molecular modeling.
• Discrepancies exist between Einstein-Smoluchowski (E-S) and Green-Kubo (G-K) methods for complex molecules.
• Accurate diffusion prediction is vital for understanding molecular dynamics.

Purpose of the Study:

• To analyze the inconsistency between E-S and G-K methods for diffusion calculations.
• To investigate the behavior of liquid n-triacontane.
• To achieve consistency in diffusion coefficient calculations for complex molecular systems.

Main Methods:

• Molecular dynamics simulations of liquid n-triacontane.
• Analysis of the velocity autocorrelation function (VACF), including long-time tails.
• Calculation of diffusion coefficients using both E-S and G-K formalisms.

Main Results:

• Non-conventional long-time tails were identified in the VACF of n-triacontane.
• The temperature dependence of the VACF tail decay exponent was determined.
• Incorporating long-time tail contributions reconciled the E-S and G-K methods.

Conclusions:

• Proper inclusion of VACF long-time tails resolves E-S/G-K method inconsistencies for n-alkanes.
• System size and force field parameters influence diffusion rate precision.
• Hydrogen nuclear quantum effects are likely the final challenge for accurate n-alkane simulation.