Polymorphism of CsI

Ab initio total energy calculations based on density functional theory and the generalized gradient approximation in conjunction with a constant-pressure minimization algorithm have been used to investigate the pressure-induced structural phase transitions in CsI. According to the calculations, increasing the pressure above approx. 20 GPa causes a small continuous distortion of the ambient pressure B2 structure. At higher pressures, a weakly first-order isosymmetric transition occurs at approx. 47 GPa. The high-pressure polymorph has an orthorhombic 'hcp-like' structure with space group Pmma. (author)