Using the local-density approximation, and calculating the Hellmann-Feynman forces, the stability of the perovskite-like structures of CaTiO3 have been studied by applying the direct method and deriving the phonon dispersion relations. The cubic Pm3m phase shows dispersionless soft phonon branch spreading from R to M points of the cubic Brillouin zone. Low-symmetry phase lAlmcm can be considered as a result of the soft mode condensation at R point. The experimentally observed Pmnb phase is a consequence of the intersection of Imma and PA/mbni space groups, being the result of soft mode condensation at R and M points, respectively. Thus, the Pmnb can be regarded as simultaneous condensations of two soft modes. The phonpn dispersion relations of Pmnb suggest that this phase is stable.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry