Molecular electrostatic properties of ions in an ionic liquid

Abstract

We have analysed the electronic wave functions from an ab initio simulation of the ionic liquid (room temperature molten salt) dimethyl imidazolium chloride ([dmim][Cl] or [C₁mim][Cl]) using localized Wannier orbitals. This allows us to assign electron density to individual ions. The probability distributions of the ionic dipole moments for an isolated ion and for ions in solution are compared. The liquid environment is found to polarize the cation by about 0.7 D and to increase the amplitude of the fluctuations in the dipole moments of both cation and anion. The relative changes in nuclear and electronic contributions are shown. The implications for classical force fields are discussed.

Keywords:

• Ionic liquid
• Electrostatic properties
• Electronic wave functions
• Room temperature molten salt

Acknowledgements

We thank EPSRC (grants GR/S41562/01, GR/S181066/01 and EP/D029538/1) and the Leverhulme Trust (Emeritus Fellowship to RMLB) for financial support. We thank Dr Yan and co-workers for communicating the results of 22 before publication. CERP thanks CAPES anc CNPQ for financial support.