Computational study of room temperature molten salts composed by 1-alkyl-3-methylimidazolium cations-force-field proposal and validation

We present a complete force field for liquid-state simulations on ionic liquids containing 1-ethyl-3-methylimidazolium and 1-n-butyl-3-methylimidazolium cations and the tetrachloroaluminate and tetrafluoroborate anions. The force field is compatible with the AMBER methodology and is easily extendable to other dialkylimidazolium salts. On the basis of the general AMBER procedures to develop lacking intramolecular parameters and the RESP approach to calculate the atomic point charges, we obtained an all-atom force field which was validated against the experimental density, diffusion coefficient, vibrational frequencies, as well as X-ray (crystal state) and neutron (liquid state) diffraction structural data. Moreover, molecular mechanics calculations for the developed force field produce the cation's structures and dipole moments in very good agreement with quantum mechanical ab initio calculations. In addition, a basic study concerning the simulated liquid structure in terms of the radial distribution functions has been undertaken using molecular dynamics simulation. In summary, we achieved a very consistent picture in the computed data for the four room-temperature molten salts.