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Abstract
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Molecular dynamics (MD) simulation was accomplished to study the thermodynamic, structural, and dynamical
properties of 1-ethyl-3-methylimidazolium methylsulfate [Emim][MeSO4] ionic liquid (IL) at different temperatures
and atmospheric pressure. The calculated density, thermal expansion coefficient, diffusion coefficient, and
electrical conductivity were in good agreement with experimental data. Our results indicated that the large deviation
between calculated ionic conductivity from Nernst-Einstein approximation and experimental data is
corrected by considering the role of counterion joint translations. Also considering the ion-ion, co-ion and counterion
coupling effects in ionic conductivity calculating with collective mean square displacement from the Einstein
law improved the accuracy of the calculated ionic conductivity. The low activation energies and short
relaxation times of hydrogen bond (HB) as well as low enthalpy of HBs disclose that the effect of HB compared
to columbic interactions in determining the structural and dynamical properties in this IL is not prevailing. The
HB dissociation takes place in subpicosecond duration with a quick rotation of anions without translational motions
but fracture ion-pair happens with great criterion translational motion of cation and anion in the nanosecond
regime. The connection between counterions exchange that is the microscopic property and macroscopic
diffusion process is proven with the closeness of activation energies and relaxation time of ion-pairing and
diffusion.
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