Parsons, DrewNinham, Barry2015-12-100743-7463http://hdl.handle.net/1885/54219Ab 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.201010.1021/la902533x2015-12-09