Ions in solutions: Determining their polarizabilities from first-principles

Abstract

Dipole polarizabilities of a series of ions in aqueous solutions are computed from first-principles. The procedure is based on the study of the linear response of the maximally localized Wannier functions to an applied external field, within density functional theory. For most monoatomic cations (Li(+), Na(+), K(+), Rb(+), Mg(2+), Ca(2+) and Sr(2+)) the computed polarizabilities are the same as in the gas phase. For Cs(+) and a series of anions (F(-), Cl(-), Br(-) and I(-)), environmental effects are observed, which reduce the polarizabilities in aqueous solutions with respect to their gas phase values. The polarizabilities of H((aq)) (+), OH((aq)) (-) have also been determined along an ab initio molecular dynamics simulation. We observe that the polarizability of a molecule instantaneously switches upon proton transfer events. Finally, we also computed the polarizability tensor in the case of a strongly anisotropic molecular ion, UO(2) (2+). The results of these calculations will be useful in building interaction potentials that include polarization effects.

Accurate Determination of Ion Polarizabilities in Aqueous Solutions

“…Similar trends were seen in other studies. 15,18,19,22 However, there is no clear theoretical argument from past literature to explain how the aqueous environment reduces the anion polarizability from its gas-phase value. Qualitatively, the reduction in polarizability in the aqueous phase relative to the gaseous phase could be due to the overlap between the electron cloud of the anions and those of the solvent molecules, which might reduce the ability of the anions to develop induced dipoles.…”

“…In order to obtain the polarizability of a single ion in water, a reference polarizability value needs to be defined. Earlier work 15,18,19,33 suggested that the polarizabilities of small cations are largely unaffected by the aqueous environment. In addition, the smaller value of the polarizability of smaller cations makes them appropriate choices as references since this will minimize the errors -the errors will be bounded by the value of the polarizability of the reference ion.…”

“…16 However, ion polarizabilities in the aqueous phase can be significantly different from their corresponding the gas-phase values 17,18 due to the strong interactions between the charge of ions and the permanent or induced dipoles of solvent molecules. 19 Unfortunately, Pauling's theoretical framework cannot be readily extended to calculate polarizabilities of ions to account for these interactions in the aqueous phase.…”

“…A range of methods with different levels of complexity have been developed, including density functional theory with Car-Parrinello molecular dynamics, 18,20 and ab initio quantum calculations with Car-Parrinello molecular dynamics. 21 However, computer simulations necessarily involve approximations in the modeling and treatment of the ions and the solvent species.…”

Effect of Ion Pairing on the Solution Dynamics Investigated by the Simulations of the Optical Kerr Effect and the Dielectric Relaxation Spectra

“…75 The z and y directions for water are along the dipole and perpendicular to the molecular plane, respectively. For the ion polarizability, the model developed by Salanne was used, 76 in which the off-diagonal components were set to be 0 and the diagonal components were set to be 0.08 3 and 3.5 3 for Mg 2+ and Cl − , respectively. T(r ij ) is the dipole tensor between molecules i and j.…”