<div><p>We study the correlations length of
the charge-charge pair correlations in concentrated electrolyte solutions by
means of all-atom, explicit-solvent molecular dynamics simulations. We
investigate LiCl and NaI in water, which constitute highly soluble, prototypical
salts for experiments, as well as two more complex, molecular electrolyte
systems of lithium bis(trifluoromethane)sulfonimide (LiTFSI), commonly employed
in electrochemical storage systems, in water and in an organic solvent mixture
of dimethoxyethane (DME) and dioxolane (DOL). Our simulations support the
recent experimental observations as well as theoretical predictions of a
non-monotonic behavior of the correlation length with increasing salt
concentration. We observe a Debye-Hückel like regime at low concentration,
followed by a minimum reached when <i>d/λ<sub>D</sub></i> = 1, where <i>λ<sub>D</sub></i> is the Debye
correlation length and d the effective ionic diameter, and an increasing
correlation length with salt concentration in very concentrated electrolytes.
As in the experiments, we find that the screening length in the concentrated
regime follows a universal scaling law as a function <i>d/λ<sub>D</sub></i> for all
studied salts. However, the scaling exponent is significantly lower than the
experimentally measured one, and lies in the range of the theoretical
predictions based on much simpler electrolyte models.</p>
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Correlation Length in Concentrated Electrolytes: Insights from All-Atom Molecular Dynamics Simulations
