In this paper we show by using static DFT calculations and classical molecular dynamics simulations that the charge transfer between ionic liquid ions plays a major role in the observed discrepancies between the overall mobility of the ions and the observed conductivities of the corresponding ionic liquids, while it also directly suppresses the association of oppositely charged ions, thus the ion pairing. Accordingly, in electrochemical applications of these materials it is important to consider this reduction of the total charges on the ions, which can greatly affect the performance of the given process or device in which the ionic liquid is used. By slightly shifting from the salt-like to a molecular liquid-like system via the decreased charges, the charge transfer also fluidizes the ionic liquid. We believe that this vital information on the molecular level structure of ionic liquids offers a better understanding of these materials, and allows us to improve the a priori design of ionic liquids for any given purpose.

In the present article we briefly review the extensive discussion in literature about the presence or absence of ion pair-like aggregates in ionic liquids. While some experimental studies point towards the presence of neutral subunits in ionic liquids, many other experiments cannot confirm or even contradict their existence. Ion pairs can be detected directly in the gas phase, but no direct method is available to observe such association behavior in the liquid, and the corresponding indirect experimental proofs are based on such assumptions as unity charges at the ions. However, we have shown by calculating ionic liquid clusters of different sizes that assuming unity charges for ILs is erroneous, because a substantial charge transfer is taking place between the ionic liquid ions that reduce their total charge. Considering these effects might establish a bridge between the contradicting experimental results on this matter. Beside these results, according to molecular dynamics simulations the lifetimes of ion-ion contacts and their joint motions are far too short to verify the existence of neutral units in these materials.

In this work, structural and dynamical properties of the binary mixture of 1-ethyl-3-methyl-imidazolium chloride and 1-ethyl-3-methyl-imidazolium thiocyanate are investigated from ab initio molecular dynamics simulations and compared to the pure ionic liquids. Furthermore, the binary mixture is simulated with two different densities to gain insight into how the selected density affects the different properties. In addition, a simple NMR experiment is carried out to investigate the changes of the chemical shifts of the hydrogen atoms due to the composition of the mixture.

Ab initio molecular dynamics simulations at elevated temperature are carried out to investigate the microscopic structure of liquid mixtures (deep eutectic solvents) composed of 1:1 and 1:2 choline chloride:ethylene glycol ([Ch]­Cl:EG) and 1:2:1 choline chloride:ethylene glycol:water ([Ch]­Cl:EG:water). In the present study, we aim to understand the composition effect on the choline chloride:ethylene glycol deep eutectic solvent and whether there is a specific composition in these solvents with marked special behavior at the microscopic level. The role of hydrogen bonds between all components was investigated through distribution functions. The structures are governed by the balance of hydrogen bond networks and the different populations of the EG molecule conformations. In the water-containing system, water competes for association with the anion. Also, the charge distribution analysis, which is consistent with structural analysis, indicates that the results are not impacted by changing composition. In addition, the charge transfer observed between ions, EG, and water molecules appears to be significant.

Power spectra of several imidazolium-based ionic liquids, 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium dicyanamide 5, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium thiocyanate, and 1-butyl-3-methylimidazolium dicyanamide, are presented based on ab initio molecular dynamics simulations. They provide an alternative tool of analysis of several electronic structure-based properties, in particular, those related to the strength of hydrogen bonding in liquids. Moreover, they can be employed to interpret experimental IR or Raman spectra, avoiding the additional calculations required for theoretical IR or Raman spectra. The obtained power spectra are shown to be in good agreement with experimental spectra, and electronic structure properties related to them are analyzed. Further, there are indications for a locality of the power spectra on a relatively short time scale of ≈10 ps or system size of about 8 ion pairs as already speculated in previous work.