Molecular dynamic simulations of ionic liquids:: A reliable description of structure, thermodynamics and dynamics

The parameterization of a new force-field and its validation for the liquid description of five imidazolium-based ionic liquids [C(n)mim][NTf2] (n = 1,2,4,6,8) are described. The proposed force-field is derived to reproduce densities, self-diffusion coefficients for cations and ions as well as NMR rotational correlation times for cations and water molecules in [C(2)mim][NTf2]. The temperature dependence and the cation chain-length dependence of these properties is described well. Very good agreement between simulated and experimental values for the heats of vaporization, shear viscosities and NMR rotational correlation times is also achieved. All properties are crucial for understanding the nature and interaction of ionic liquids. The good performance of the new force-field suggests that the Lennard-Jones interactions previously were strongly overestimated. The given force-field now allows us to investigate other important properties of this class of ionic liquids such as the micro segregation of ionic liquids, ion pair formation, lifetimes of ion pairs and the solvent dependency of these properties.