**A combined QTAIM, DFT and molecular dynamics study on the nanoscale
dynamical and structural organization of imidazolium-based dicationic
ionic liquids**

ZO Memar and M Moosavi, JOURNAL OF MOLECULAR LIQUIDS, 365, 120186 (2022).

DOI: 10.1016/j.molliq.2022.120186

In this work, the effects of linkage alkyl chain length on the dynamical
and structural micro-heterogeneities of some imidazolium-based
dicationic ionic liquids (DILs) i.e. **Cn(mim)2****BF4**2, (n = 3, 6, 9, and
12) were studied via quantum mechanical calculations and also classical
molecular dynamics (MD) simulations. Hydrogen bondings and also the
interaction energies between the studied ions have been calculated using
the density functional theory (DFT) calculations and also the quantum
theory of atoms in molecules (QTAIM) method. The results showed that
with increasing the linkage alkyl chain length of DILs, the interaction
energies and electron densities are decreased, because the electro-
static interactions in DILs are weakened with increasing the -CH2 groups
in the linkage chain. Different kinds of combined distribution functions
(CDFs) were computed to better understand the ori-entations of ions in
the studied DILs. Although, two rings of cation are almost perpendicular
with respect to each other in all studied DILs, the orientation of
linkage chain with respect to the rings is different in short-and long-
linkage chain DILs. To understand the arrangement of the nearest
neighboring ions, neighborhood analysis and spatial distribution
functions (SDFs) of ions were analyzed. Furthermore, the mean square
displacement (MSD), non-Gaussian parameter, van Hove correlation of
cation and anions and also the ion pair, ion cage, hydrogen bond and
reorientation dynamics were computed. DILs with longer alkyl chain
length have more deviation in non-Gaussian parameter and Gaussian behav-
ior of distribution of particle displacements, probably due to weakening
the electrostatic interactions. Also, they have higher ion cage/ion pair
stabilities than DILs with shorter linkage chain. Altogether, the
linkage chain length in DILs has significant influences on their
organizations in such a way that with increasing linkage chain length,
their dynamical and structural micro-heterogeneities increase. (C) 2022
Elsevier B.V. All rights reserved.

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