The ion dynamics and the chemical bonding properties in the non-superionic, superionic and molten phases of CuI are studied by means of ab initio molecular dynamics simulations. The temperature dependence of the bonding properties is investigated by calculating the gross atomic charge and the overlap population between the atoms in the three phases mentioned above. It is shown that the average values of the gross atomic charges and their distribution widths increase with the increase of temperature. The time evolution of the electronic states around mobile Cu ion has been also calculated, which reveals clearly that the bonding changes accompanying the ion movement. In particular, it is shown that the p-electron component of the Cu ion contributes mainly to the time evolution of the total gross charge. In the superionic phase, it is shown that the covalent bonding of the Cu ion weakens when it migrates between neighboring tetrahedral sites, and that the ionicities for the Cu ions at the octahedral sites are larger than those for the Cu ions at the tetrahedral sites. (c) 2005 Elsevier B.V All rights reserved.