title: Effect of pore wall model on prediction of diffusion coefficients for graphitic slit pores.
abstract: The effect of the pore wall model on the self-diffusion coefficient and transport diffusivity predicted for methane in graphitic slit pores by equilibrium molecular dynamics (EMD) and non-equilibrium MD (NEMD) is investigated. Three pore wall models are compared--a structured wall and a smooth (specular) wall, both with a thermostat applied to the fluid to maintain the desired temperature, and a structured wall combined with the diffuse thermalizing scattering algorithm of MacElroy and Boyle (Chem. Eng. J., 1999, 74, 85). Pore sizes ranging between 7 and 35 angstroms and five pressures in the range of 1-40 bar are considered. The diffuse thermalizing wall yields incorrect self-diffusion coefficients and transport diffusivities for the graphitic slit pore model and should not be used. Surprisingly, the smooth specular wall gives self-diffusion coefficients inline with those obtained using the structured wall, indicating that this computationally much faster wall can be used for studying this phenomenon provided the fluid-wall interactions are somewhat weaker than the fluid-fluid interactions. The structured wall is required, however, if the transport diffusivity is of interest.
authors.affiliation: Institute for Materials and Processes, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, UK EH9 3JL.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Cai
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Biggs
authors.forename: Nigel A
authors.initials: NA
authors.lastname: Seaton