Theoretical calculation of the physico-chemical properties of 1-butyl-4-methylpyridinium based ionic liquids

Ionic liquids (ILs) have attracted much attention for their unique physicochemical properties, which can be designed as needed by altering the ion combinations. Besides experimental work, numerous computational studies have been concerned with prediction of physical properties of ILs. The results of molecular dynamics simulations of ILs depend strongly on the proper force field parameterization. Classical force fields and the force fields designed specifically for ILs have been found to yield diffusion' coefficients, that are too low for the liquid state. This has been attributed to the lack of electronic polarizability in the most force fields. One simple solution to this problem has been uniform by scaling down of the partial charges of all ions. In this work we investigated the influence of the charge scaling, the size of the simulated system and the temperature factor on calculated density, radial distribution function and the diffusion coefficients of the cation and anion of two methylpyridinium based ionic liquids: 1-butyl-4-methylpyridinium tetrafluoroborate ([b4mpy][BF4]) and 1-butyl-4-methylpyridinium chloride ([b4mpy][Cl]). We show that the parameterization is the key for a proper reproduction of the diffusion coefficient and as a consequence the melting temperature and ionic conductivity. We were also able to get some structural informations on the cation-anion relationships in the investigated ILs. (C) 2016 Elsevier B.V. All rights reserved.