Fick diffusion coefficients via molecular dynamics: An alternative approach in the Fourier domain

Mutual diffusion coefficient data are required for several systems of scientific and engineering interest to properly describe mass transport phenomena over a wide range of pressures, temperatures, and compositions. In this work, we calculated Fick diffusion coefficients for some CO2 and n-alkane mixtures at high pressures using a new method, which we derived by introducing modifications to the Fourier Correlation Method (FCM) originally proposed by Nichols and Wheeler [I&EC Research, 54, 12,156-12,164 (2015)]. The modified FCM (mFCM) results were validated through comparisons with experimental data and with Fick coefficients calculated by employing well-established Molecular Dynamics methodologies. The new approach has some interesting advantages, such as providing Fick coefficients for molecular systems directly through a single equilibrium calculation, in contrast to traditional methods in which an extra calculation is needed to obtain the so-called thermodynamic factor. It is shown that the new approach considerably reduces the finite-size effect of the simulation box on the calculated diffusion coefficients, which are thus obtained in the thermodynamic limit. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study presents a new method for calculating Fick diffusion coefficients for high-pressure CO2 and n-alkane mixtures by modifying an existing method. The new approach simplifies the calculation process, providing diffusion coefficients directly and reducing the impact of simulation box size on the results.