Work function change of platinum electrodes induced by halide ad-

8 The properties of a halogen-covered platinum (111) surface have been studied using density func9 tional theory (DFT) as halides are often present at electrochemical electrode/electrolyte interfaces. 10 We focused in particular on the halogen-induced work function change as a function of coverage 11 of fluorine, chlorine, bromine and iodine. For electronegative adsorbates, an adsorption-induced 12 increase of the work function is usually expected, yet we find a work function decrease for Cl, Br 13 and I which is most prominent at a coverage of approximately 0.25 ML. This coverage-dependent 14 behavior can be explained through a combination of charge transfer and polarization effects on the 15 adsorbate layer. The results are contrasted to the adsorption of fluorine on calcium, a system in 16 which a decrease in the work function is also observed despite involving large charge transfer to 17 the halogen adatom. 18