Study of 1,3-dimethylimidazolium chloride with electronic structure methods and force field approaches

The 1,3-dimethyl imidazolium chloride [MMIM]Cl is an example of ionic liquid and frequently studied in literature. In this article [MMIM]Cl is studied using an ab initio method [second order Møller-Plesset perturbation theory (MP2), density functional theory (DFT)] and classical force field approach with the aim of looking at some properties on different scales. Selected properties are studied with the different methods and compared to each other. The comparison between the results obtained with MP2 and the DFT approach allows us to comment on the validity of this latter and thus on its employment in larger systems. On the other hand, the comparison between the DFT results and those of the classical approach allows us to test the reproducibility of electrostatic properties by this latter approach. As the results show the used DFT setup is rather satisfactory, while the classical force fields are describing the electrostatic properties in an insufficient way. A revision (improvement) of the classical force fields is at this stage necessary in order to capture the electrostatic properties in a proper way.