Direct calculation of mutual diffusion coefficients of binary system using non-equilibrium molecular dynamics simulation

Abstract

Molecular dynamics (MD) simulation is widely used to calculate transport properties of fluids.In this study, non-equilibrium molecular dynamics (NEMD) simulation was applied to calculate mutual diffusion coefficients from the molecular flux at a given concentration gradient. First, the applicability of spherical molecular model was investigated by calculating self-and tracer diffusion coefficients of methane and n-decane mixture by a equilibrium MD simulation. The simulated self-and tracer diffusion coefficients of both components were in good agreement with literature data except in the case that methane molar fraction was nearly equal to zero. Further, the NEMD simulation was adopted to calculate mutual diffusion coefficients of binary system of methane and n-decane. This binary system exhibits anomalous concentration dependence of mutual diffusion coefficients in the vicinity of critical molar fraction according to the previously reported experimental data. The NEMD simulation well reproduced such concentration dependence of mutual diffusion coefficients.The simulation also gave a fairly good agreement with the calculated results by the Darken equation using tracer diffusion coefficients with a thermodynamic factor.

Thermodynamics of Oiling-Out in Antisolvent Crystallization. II. Diffusion toward Spinodal Decomposition

“…A challenge in nonideal multicomponent liquid diffusion is that multicomponent diffusivity data are rarely available. The values of M–S diffusivities still rely on molecular dynamic simulations − and empirical relations, ,− such as the Darken-type equations , and the Vignes-type relations. ,, The Darken equation , is widely used to describe mutual diffusion coefficients in binary mixtures, considering both hydrodynamics and thermodynamics, cf. Section S1 in the Supporting Information.…”

Application of Reverse Nonequilibrium Molecular Dynamics to the Calculation of the Mutual Diffusion Coefficient of Alkane Mixtures

“…Studies on mass transport in liquids by mutual diffusion are of fundamental importance for many applications in biology, chemistry, and chemical engineering. − Accurate measurement of mutual diffusion coefficients over wide ranges of pressure and temperature is necessary because of its importance in the design of extractors, reactors, separators, and so on . Fick’s law and Maxwell–Stefan (MS) theory are commonly used to describe mutual diffusion in mixtures .…”

“…Then, the thermodynamic factor is multiplied by the MS diffusion coefficient to evaluate Fick diffusion coefficient . The methods for the calculation of mutual diffusion coefficient from MD simulations have been reviewed by Liu et al Numerous equilibrium MD (EMD) simulations have been performed to evaluate mutual diffusion coefficients of binary and ternary systems; for examples, see references. − A few researchers have also performed nonequilibrium molecular dynamics (NEMD) simulations to determine the mutual diffusion coefficient of binary systems. ,− …”

“…1−3 Accurate measurement of mutual diffusion coefficients over wide ranges of pressure and temperature is necessary because of its importance in the design of extractors, reactors, separators, and so on. 4 Fick's law and Maxwell−Stefan (MS) theory are commonly used to describe mutual diffusion in mixtures. 5 Fick diffusivities (D 12 ) are readily accessed from experiments since they are defined in terms of measurable concentration gradients.…”