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

Abstract

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.