Theoretical characterization of the high-pressure phases of PbF2

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