The symmetry rules for the second order phase transitions (in phenomenological Landau theory) are considered and applied to perovskites:BaTiO3, BaZrO3, BaHfO3, StTiO3 and LaCoO3. Basing on the space group induced by representations theory, the phonon symmetry is found for the systems under consideration. The direct method of phonon calculation (frozen phonon approach) is discussed. The results of ab initio LCAO frozen phonon calculations on cubic phase of perovskites are presented. It is demonstrated that these results agree both with the predictions of the isotropy group theory and experimental data for high and low symmetry phases of perovskites.
„Phase transitions and ab inito calculations of phonons in perovskites”){kind=link}