Comparison between two solar minimum model runs, one with ion-neutral (IN) collisions only (dashed) and the other one with both ion-neutral and ion-ion (II) Coulomb collisions (solid). The black lines show the total ion density profiles obtained by the two model runs, whereas the red and blue lines correspond to the density profiles of the group I and II ions, respectively. The former includes all ion species with peak altitudes above 200 km and the latter includes the remaining species.