Short communication: Investigation on dynamics and self-diffusion coefficient of [BMIM][PF6] via molecular dynamics simulations

In this article, velocity autocorrelation function (VACF) and mean-square displacement (MSD) for [BMIM][PF6] at different temperatures are analyzed in detail via molecular dynamics simulations. The self-diffusion coefficients are obtained from the integration of VACF function in the range of 0-25 ps and from the linear slope of MSDs in the range of 100-900 ps. Our results indicate that the self-diffusion coefficients temperature dependence is observed by following the empirical Arrhenius equation. The relative errors of the self-diffusion coefficients decrease significantly with increasing temperature under the same simulation time and time step. Furthermore, the self-diffusion coefficients calculated from the Einstein relation at different temperatures are all higher than that from the Green-Kubo formulas. The former obviously has higher calculation precision than the latter. Several reasons for the above conclusions are discussed in details. The experimental temperature trend of the self-diffusion coefficients is well reproduced by both methods. The fitting results from the Einstein relation extrapolating to room temperature are also compatible with the experimental values.