Molecular simulation of guanidinium-based ionic liquids

A new systematic all-atom force field was developed for cyclic guanidinium-based ionic liquids (ILs) based on the AMBER force field. Optimized molecular geometries and equilibrium bond lengths and angles were obtained by ab initio calculations, and charges were allocated to each atom center by fitting the ab initio electrostatic potential. Molecular dynamics simulations were performed for eleven kinds of ILs that are comprised of NO3(-) anions and cyclic guanidinium-based cations. Validation was carried out by comparing our simulated densities with experimental and calculated data from the literature. Transport properties such as self-diffusion coefficients, viscosities, and conductivities were calculated by molecular dynamic simulation, and their dependence on the length of the alkyl chains of cyclic guanidinium-based cations are discussed. Radial distribution functions and spatial distribution functions were investigated to depict the microscopic structures of the ILs, and the relationship between their properties and microstructures is also discussed.