We have performed density functional calculations for the structures and stabilities of Al13I at the scalar relativistic pseudopotential and all-electron levels of theory. The Al-13 moiety in Al13I is significantly distorted and structurally similar to an Al-13 cation, where the natural population is -0.27e for the I atom. Unlike other Al-13-M (M=H, alkali metals, and coinage metals) clusters, a C-s-ontop structure was found to be the most stable form. The Al13I cluster has a large Al-13-I binding energy of 3.11 eV and is more stable, as charge transfer to the electronegative I atom is larger. (C) 2004 American Institute of Physics.