Electron density and energy density view on the atomic interactions in SrTiO₃

The results of topological analysis of the electron density in an SrTiO₃ crystal based on the experimental (at 145 K) and theoretical data are presented and discussed. The features of the electron density lead to the conclusion that the Ti-O interaction is of the partly polar covalent (or intermediate) type. Complicated atomic shapes defined by the zero-flux surfaces in the electron density are revealed. It is found that, in general, they are far from spherical and have very slight asphericity in the close-packed layers. The topological coordination numbers of Sr and Ti are the same as the geometrical numbers, whereas the topological coordination for the O atom (6) differs from the geometrical value (12). The latter results from the specific shape of the Ti-atom basin, which prevents bond-path formation between the O atoms. The analysis of the kinetic and potential energy densities derived from the electron density using the density functional theory formulae revealed the stabilizing crystal-forming role of the O atoms in SrTiO₃. Structural homeomorphism between the experimental electron density and the potential and kinetic energy densities is observed.