Dielectric response of concentrated NaCl aqueous solutions: Molecular dynamics simulations

Abstract

Molecular dynamics simulations are performed to study the dielectric response of concentrated NaCl aqueous solutions. The extended simple point charge interaction potential for water molecules and the Higgis–Mayer potential for ion–ion interactions are used. The ion–ion and ion–water distributions are examined for 1 M solution at 298, 373 and 473 K. The solvate-separated ion pairs with the Na+–Cl− separation of about 5.0 Å are found to form preferentially at ambient temperature. The close contact pairs with the ion–ion separation of 2.9 Å tend to form in high temperature solution. The 3D water–ion arrangements are revealed with the aid of the spatial distribution function. The Na+–O–Cl− angle in the solvate-separated ion pairs is found to be close to 106°. The correlation times of translations, τT, and rotations, τR, for water molecules in the solvation shells of the cation and anion are determined. The frequency-dependent dielectric permittivity and absorption coefficient for the concentrated NaCl solution are calculated over wide temperature range. The origin of the complex dielectric spectra for concentrated NaCl solution is analyzed.