Influence of rotational instability on the polarization structure of SrTiO3

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 paper, we rigorously prove—both numerically and analytically—that a 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 nonrotational SrTiO₃ , revealing that polarization structure is sensitive to structure distortion caused by oxygen-octahedra rotation and promises to be an effective tool for studying material properties. (3) Furthermore, from the polarization structure we determine the microscopic Wannier-function interactions in SrTiO₃ . These interactions are found to vary significantly with and without oxygen-octahedra rotation.