Dielectric behavior of propylene carbonate solutions with LiPF6, LiClO4, and LiBF4. II. Molecular dynamics simulation study

Abstract

Propylene carbonate (PC) solutions with three different lithium salts (LiPF6, LiClO4, and LiBF4) were investigated by combining experimental dielectric relaxation spectroscopy (DRS) and molecular dynamics (MD) simulations. Although DRS spectra include rich information regarding microscopic structure and local dynamics in solution systems, the interpretation of spectra is not straightforward and needs complementary analysis. In this work, we applied MD simulations to the PC solutions and demonstrated that the experimental spectra are well reproduced by MD. The simulation results display the decomposed signals, which, respectively, correspond to individual components such as PC and ion pairs. The signal decomposition enables the quantification of essential variables such as rotational relaxation time and relaxation intensity for each component. In addition, the effective dipole moments of individual components were estimated based on the Cavell equation and the simulated results, which agree well with the effective dipole moments obtained from experimental data. It was also shown that the effective dipole moments for some species are smaller than their corresponding unit dipole moments derived from atomic charges and coordinates. This reflects the fact that DRS spectra capture the collective motion of dipoles in solution systems.