Theoretical characterization of the high-pressure phases of PbF2

Ab initio perturbed ion calculations were performed for the cubic, orthorho mbic, hexagonal, and monoclinic phases of PbF2. A complete characterization of these phases was achieved in terms of the potential energy surfaces, th e equations of state, and the phase-transition pressures. Thermal effects w ere included via a quasiharmonic nonempirical Debye model. The internal par ameters of the unit cell of each phase were reoptimized at each volume to g enerate the energy surface. The calculated results are in good agreement wi th the experimental data available for the cubic and orthorhombic phases. T he results predict the hexagonal phase to be the high-pressure post-cotunni te structure for PbF2, since the monoclinic phase is seen to collapse into the hexagonal phase during the optimization at high pressures.