Phonons and heat capacity of LaAlO3

The ab initio calculations of the phonon dispersion relations for cubic and rhombohedral phases of LaAlO3 were performed using the density functional perturbation theory together with plane-wave expansion and norm conserving pseudopotentials. In the cubic phase the phonon dispersion curves show a soft mode at the R-point. This soft mode leads to the observed cubic-rhombohedral phase transition. The phonon dispersion relations of rhombohedral LaAlO3 confirm the dynamical stability of this phase. The calculated heat capacity of rhombohedral LaAlO3 is in very good agreement with available experimental result.