Ionic potential models in insulators having the rutile structure

There have been extensive experimental and theoretical studies of the properties of defects in insulators, primarily for cubic systems like the alkali halides, the alkaline-earth oxides, and fluorite structure crystals. Recently, calculations of defect properties have been done for materials of lower symmetry such as α-alumina and insulators that have the rutile structure. The potential model used in these calculations is the shell model, whose constituents are the charged ion cores and electronic shells, with the shells bound harmonically to their cores and with long-range Coulomb interactions between the charged constituents. They apply this model to TiO2 and MnF2