First-principles self-consistent total-energy calculations within the local-density approximation show, in agreement with experiments, that CsI undergoes a transition from the cubic (CsCl) structure to a tetragonal structure at a pressure Pt approximately=40 GPa. The calculated volume at the transition is approximately 53\% of the zero-pressure volume. The authors find that the phase transition is driven by an 'intercellular' electrostatic interaction. A structural bistability is found around the transition.
 

Physical Review Letters, 55 600-3, 1985.