Molecular dynamics simulations of longer n-alkanes in silicalite: state-of-the-art models achieving close agreement with experiment.

The diffusion of longer n-alkanes (n-C8-n-C16) in silicalite was studied using molecular dynamics (MD) simulations at a temperature range of 300-400 K, with loadings appropriate for direct comparison with previously carried out quasielastic neutron scattering (QENS) studies. The calculated diffusion coefficients were in close agreement with experimental values, significantly closer than those calculated using more primitive framework and hydrocarbon models, and in the case of the longer alkanes, closer agreement than those calculated by MD studies using the same model, but not using experimental loadings. The calculated activation energies of diffusion agreed with experiment to within 1.5 kJ mol(-1) for shorter alkanes of the range, but with a larger difference for tetra and hexadecane, due to factors which cannot be reproduced using periodic boundary conditions. Channel switching between the straight and sinusoidal channel system was found for octane at higher temperatures, where more than one octane molecule was located in the channel, which was attributed to the molecular size of octane, and the repulsion caused by the presence of the extra octane molecules in the channel system, allowing the potential barrier of channel switching at the junctions to be breached.