Polarizability effects on the structure and dynamics of ionic liquids

Abstract

Polarization effects on the structure and dynamics of ionic liquids are investigated using molecular dynamics simulations. Four different ionic liquids were simulated, formed by the anions Cl(-) and PF6(-), treated as single fixed charge sites, and the 1-n-alkyl-3-methylimidazolium cations (1-ethyl and 1-butyl-), which are polarizable. The partial charge fluctuation of the cations is provided by the electronegativity equalization model (EEM) and a complete parameter set for the cations electronegativity (χ) and hardness (J) is presented. Results obtained from a non-polarizable model for the cations are also reported for comparison. Relative to the fixed charged model, the equilibrium structure of the first solvation shell around the imidazolium cations shows that inclusion of EEM polarization forces brings cations closer to each other and that anions are preferentially distributed above and below the plane of the imidazolium ring. The polarizable model yields faster translational and reorientational dynamics than the fixed charges model in the rotational-diffusion regime. In this sense, the polarizable model dynamics is in better agreement with the experimental data.

Raman band shape analysis of cyanate-anion ionic liquids

“…It is known that non-polarizable models for MD simulation of ionic liquids usually result in sluggish dynamics in comparison with the real system. Inclusion of polarization effects increases diffusion coefficient and ionic conductivity, and decreases the viscosity of the simulated system [24,64]. Nevertheless, the issue here is only a comparison of reorientational dynamics of the main symmetry axis of Fig.…”

Molecular Dynamics Simulations of Ionic Liquids and Electrolytes Using Polarizable Force Fields

“…This is the most common option, in particular if only one ionic species is made polarizable. 88,89 Charge transfer is allowed between an ion pair: 90 However, the complete assignment which cation i belongs to which anion j is ambiguous as a particular anion may have the shortest distance from several cations. Nevertheless, temporary charge transfer between cations and anions can be realized this way.The total charge of the system is zerowhich should always be the case, even if the charge flow is restricted otherwise.…”

Quantum Chemical Modeling of Hydrogen Bonding in Ionic Liquids

“…The development of polarisable force fields able to recover the “sloshing” of charge within an ion is highly desirable, particularly if H-bonding is to be well described. It is clear that the MD representation of H-bonding in ILs needs to be improved; however, the mechanism by which this can best be achieved is less clear [90, 91]. …”