title: Molecular dynamics analysis of the effect of electronic polarization on the structure and single-particle dynamics of mixtures of ionic liquids and lithium salts.
abstract: We report a molecular dynamics study on the effect of electronic polarization on the structure and single-particle dynamics of mixtures of the aprotic ionic liquid 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)-imide ([EMIM][TFSI]) doped with a lithium salt with the same anion at 298 K and 1 bar. In particular, we analyze the effect of electron density fluctuations on radial distribution functions, velocity autocorrelation functions, cage correlation functions, mean-squared displacements, and vibrational densities of states, comparing the predictions of the quantum-chemistry-based Atomistic Polarizable Potential for Liquids, Electrolytes, & Polymers (APPLE&P) with those of its nonpolarizable version and those of the standard non-polarizable Optimized Potentials for Liquid Simulations-All Atom (OPLS-AA). We found that the structure of the mixture is scarcely modified by the fluctuations in electron charge of their constituents, but their transport properties are indeed quite drastically changed, with larger mobilities being predicted for the different species in the bulk mixtures with the polarizable force field. Specifically, the mean-squared displacements are larger for the polarizable potentials at identical time intervals and the intermediate subdiffusive plateaus are greatly reduced, so the transition to the diffusive regime takes place much earlier than in the non-polarizable media. Moreover, the correlations of the added cations inside their cages are weakened out earlier and their vibrational densities of states are slightly red-shifted, reflecting the weakening effect of the electronic polarization on the Coulomb coupling in these dense ionic media. The comparison of OPLS-AA with non-polarizable APPLE&P indicates that adding polarization to OPLS-AA is not sufficient to achieve results close to experiments.
authors.affiliation: Helmholtz-Institute Münster (IEK-12): Ionics in Energy Storage, Forschungszentrum Jülich, Corrensstrasse 46, 48149 Münster, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Lesch
authors.affiliation: Grupo de Nanomateriais e Materia Branda, Departamento de Física da Materia Condensada, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain.
authors.forename: Hadrián
authors.initials: H
authors.lastname: Montes-Campos
authors.affiliation: Grupo de Nanomateriais e Materia Branda, Departamento de Física da Materia Condensada, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain.
authors.forename: Trinidad
authors.initials: T
authors.lastname: Méndez-Morales
authors.affiliation: Grupo de Nanomateriais e Materia Branda, Departamento de Física da Materia Condensada, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain.
authors.forename: Luis Javier
authors.initials: LJ
authors.lastname: Gallego
authors.affiliation: Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Heuer
authors.affiliation: Department of Computational Biological Chemistry, University of Vienna, Währingerstrasse 17, A-1090 Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Schröder
authors.affiliation: Grupo de Nanomateriais e Materia Branda, Departamento de Física da Materia Condensada, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain.
authors.forename: Luis M
authors.initials: LM
authors.lastname: Varela