  The k-space polarization structure and its strain response in SrTiO3 with
rotational instability are studied using a combination of first-principles
density functional calculations, modern theory of polarization, and analytic
Wannier-function formulation. (1) As one outcome of this study, we rigorously
prove-both numerically and analytically-that folding effect exists in
polarization structure. (2) After eliminating the folding effect, we find that
the polarization structure for SrTiO3 with rotational instability is still
considerably different from that for non-rotational SrTiO3, revealing that
polarization structure is sensitive to structure distortion of oxygen-octahedra
rotation and promises to be an effective tool for studying material properties.
(3) Furthermore, from polarization structure we determine the microscopic
Wannier-function interactions in SrTiO3. These interactions are found to vary
significantly with and without oxygen-octahedra rotation.
