Fig. 4.

Results of electronic structure calculations. (A) Comparison of the different contributions to the interaction energy of the Na⁺ (green) and Cl⁻ (blue) ion with a negatively and positively charged Au₉ cluster model, respectively, as calculated with ωB97X-V/def2-TZVPD. While the polarization term is of equal magnitude, charge transfer is completely absent in case of Na⁺, whereas it contributes to the interaction energy for the Cl⁻ case. (B) The net charge of a grand-canonical periodic slab model with varying bias potential referenced against the computed PZC. The green (blue) data points show the corresponding decrease (increase) of the net charge upon Na⁺ (Cl⁻) binding. The change of this polarization effect is negligible in the experimental bias range (−0.15 to 0.2 V) as indicated by the constant length of the colored arrows.