Realistic ion dynamics through charge renormalization in nonaqueous electrolytes

We performed molecular dynamics (MD) simulations using several quantum chemistry parametrized force fields for lithium bistriflimide (LiTFSI) in acetonitrile. All yield solution structure that is consistent with the neutron scattering experiments (bottom), yet produce dramatically different ion dynamics (top). The discrepancies suggest that inadequate representation of long-range interactions leads to excessive ionic association and ion-pair clustering. We show that reasonable agreement with the experimental observations can be achievable by the renormalization of the ion charges using a “titration” method.

Scientific Achievement

We demonstrate that a computationally inexpensive modification non-polarizable force fields: charge renormalization, can harmonize computed and experimentally determined structure and dynamic attributes of nonaqueous electrolytes. It is sufficient to reproduce dynamics over range of 0-2 M salt while not sacrificing quality of structural properties.

Significance and Impact

Traditional force fields for nonaqueous electrolyte solutions focused mainly on the short-range properties (e.g., coordination numbers for ions). Consequently, the dynamic properties of these solutions or the clustering of the associated ions on a long timescale cannot be reproduced accurately. As these properties are important for practical applications, closer evaluations of force fields are required before in silico design of electrolytes becomes a reliable tool for prediction, and our charge renormalization method is useful in this regard.

Research Detail

  • Performed MD simulations using four force field parameters sets from quantum chemistry calculations and charge renormalization
  • Dramatically different ionic dynamics and consistent solution structures calculated from MD indicate inadequate representation of long-range interactions
  • Comparisons with experiments (neutron scattering, NMR, conductivity) reveal that charge renormalization recovered dynamics while holding the structure

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DOI: 10.1021/acs.jpcb.0c01197

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