The kaolinite (0 0 1) polar basal plane

Kaolinite is thought to be an efficient ice nucleating agent because kaolinite crystals expose perfect unreconstructed (0 0 1) basal surfaces which provide a suitable template for ice growth. However, we show here with the aid of density functional theory calculations that the unreconstructed basal surface is polar. Various mechanisms to eliminate the macroscopic dipole and in so-doing stabilize the basal surface are considered. The most promising option identified so far involves the adsorption of foreign atoms (for example, Na and Cl atoms) on the perfect basal surface, since this yields a non-metallic surface with a cleavage energy lower than the unreconstructed polar basal surface. A quantitative experimental structure determination of the kaolinite basal surface is called for.