Ionic and covalent bonds in CeO2 crystal

We have performed cluster calculations in a study of the bonding nature in the CeO2 crystal using the relativistic discrete-variational Xα method. The electron charge distribution of CeO2 is compared with those of ZrO2 and CaF2. The charge density in the metal atomic region indicates stronger covalency for CeO2 than that in Zr for ZrO2. The repulsion between the metal and oxygen ionic cores is, however, strong and superior to the covalent interaction, and thus the ionic character determines the static bonding nature in the CeO2 crystal. A population analysis shows that the mixed interaction due to the independent ionic and covalent contributions arises from the ionic Ce 5s, 5p and covalent Ce 4f, 5d orbitals which are proximate to each other in the bond region.