Programme

P.53 -- Poster, VCTP-45

Date: Tuesday, 13 October 2020

Time: 08:30 - 10:00

Non-Equilibrium Molecular Dynamics Simulations of Self-Diffusion Coefficient at Infinite Dilution: Applications to Fractionation of Noble Gases

Luc Han Tuong, Hai Hoang, Cuong Quoc Doan, Magali Pujol, Guillaume Galliero

Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City, Vietnam. Quang Binh University, Dong Hoi City, Vietnam. TOTAL S.A., CSTJF, Avenue Larribau, Pau, 64018, France. Laboratoire des Fluides Complexes et leurs Reservoirs, LFCR UMR 5150, Universite de Pau et des Pays de l’Adour, E2S UPPA, CNRS, TOTAL, Pau, France

Classical equilibrium molecular dynamics (MD) simulations using the Green-Kubo formula or Einstein’s relation have shown to be an efficient tool to compute the self-diffusion coefficient of various fluids. However, when dealing with highly dilute solutions that are rather ubiquitous in many fields including geological and petroleum engineerings, these approaches may provide simulation results for solute self-diffusion coefficient with a poor statistics and so to very large error bars. In such situations, non-equilibrium molecular dynamics (NEMD) simulations that yield high signal-noise ratio is an option to improve the uncertainties. Thus, this work aims at proposing an efficient scheme of NEMD simulations to compute the self-diffusion coefficient of solute in infinite dilution solution. To do so, we have used theory of the thermodynamics of irreversible process (TIP) to derive the approach. It has been obtained that this scheme provides very good results for bulk solutions. However, it becomes less efficient for highly confined solutions in nanoporous medium due to a non-linear response. In such cases, we have proposed an extrapolation to determine the self-diffusion coefficient of solution in the linear response regime. Finally, the proposed scheme has been employed to investigate the fractionation of noble gases by molecular diffusion in bulk water and in saturated clays.

Presenter: Lục Hán Tường

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