Calculations for antiferrodistortive phase of SrTiO3 perovskite:: hybrid density functional study

The electronic and atomic structure of SrTiO3 crystals below the antiferrodistortive phase transition observed at 105 K is calculated using the hybrid B3PW functional as implemented in the ab initio CRYSTAL-2003 computer code. Such a combination of non-local exchange and correlation permits the calculation for the first time of the TiO6 octahedron rotational angle and the ratio c/a of tetragonal lattice constants in excellent agreement with experimental data. The level splitting of the bottom of the conduction band is found to be very small, < 1 meV. The predicted phase-mtransition induced change of the optical gap from indirect to direct is confirmed by experimental photoconductivity data.