THE RELATIVE STABILITY OF THE 6-FOLD AND 8-FOLD COORDINATED STRUCTURES OF CESIUM-CHLORIDE

Quantum mechanical calculations of inter-ionic forces explain the experimental result that cesium chloride crystallizes in an eightfold rather than a sixfold co-ordinated structure at ambient temperatures. The anion charge densities become compressed in-crystal compared with free chloride ions in order to reduce the short range inter-ionic repulsions, thus maximizing the crystal cohesion. Previous theories neglected these compressions by using only pairwise additive inter-ionic interactions and consequently failed to predict the stability of the eightfold over the sixfold co-ordinated structure.