Phonon calculations in cubic and tetragonal phases of SrTiO(3): A comparative LCAO and plane-wave study: A comparative LCAO and plane-wave study

The atomic, electronic structure and phonon frequencies have been calculated in cubic and low-temperature tetragonal SrTiO₃ phases at the ab initio level. We demonstrate that the use of the hybrid exchange-correlation PBE0 functional gives the best agreement with experimental data. The results for the standard generalized gradient approximation (PBE) and hybrid PBE0 functionals are compared for the two types of approaches: a linear combination of atomic orbitals (CRYSTAL09 computer code) and plane waves (VASP5.2 code). The relation between cubic and tetragonal phases and the relevant antiferrodistortive phase transition is discussed in terms of group theory and is illustrated with analysis of calculated soft-mode frequencies at the Γ and R points in the Brillouin zone. Based on phonon calculations, the temperature dependence of the heat capacity is in good agreement with experiment.