Structures, Compressibilities, and Phase Transitions of Ionic Crystals in a Quantum‐Statistical ab Initio Theory

The structures of about 50 ionic crystals of cubic symmetry have been calculated in terms of a quantum‐statistical ab initio theory. In most cases agreement with experiment has been attained; in particular, the changes of the phases of alkali halides when the cation is replaced by a Cs ion have been obtained. In a refined crystal model the changes of size of the same ion in different lattices and the crystal compressibilities have been calculated. The examination of the phase transitions under pressure gives rather satisfactory results for the transition pressures in the cases of Na compounds. The validity of the virial theorem for the refined crystal model has been checked for the cases of CsBr and KCI.