title: Importance of accurate dynamic polarizabilities for the ionic dispersion interactions of alkali halides.
abstract: Ab initio quantum mechanical calculations of the dynamic polarizability of alkali metal and halide ions are performed as a function of imaginary frequency. Electron correlation is shown to provide a significant correction to ionic polarizabilities. Ab initio ion-surface dispersion coefficients are compared with single- and multimode London approximations. The commonly employed single-mode model with the characteristic frequency taken from the ionization potential of the ion is shown to be inadequate, underestimating dispersion forces with an average error around 40% or as high as 80% for halide ions. Decomposition of the polarizability data into five modes covers the major modes of each ion adequately (four modes for Li(+)). Illustrative calculations of surface potentials at the mica surface in aqueous alkali halide electrolytes are made. Charge reversal is obtained with the more polarizable cations, K(+) and Rb(+). The error in the single-mode ionization potential models is seen as a strong shift in the surface potential from negative toward positive values.
authors.affiliation: Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Drew F
authors.initials: DF
authors.lastname: Parsons
authors.forename: Barry W
authors.initials: BW
authors.lastname: Ninham