Ab initio calculations of PbTiO₃/SrTiO₃ (001) heterostructures

We performed ab initio calculations for the PbTiO₃/SrTiO₃ (001) heterostructures. For both PbO and TiO₂-terminations of the PbTiO₃ (001) thin film, augmented on the SrTiO₃ (001) substrate, the magnitudes of atomic relaxations Δz increases as a function of the number of augmented monolayers. For both terminations of the augmented PbTiO₃ (001) nanothin film, all upper, third and fifth monolayers are displaced inwards (Δz is negative), whereas all second, fourth and sixth monolayers are displaced outwards (Δz is positive). The B3PW calculated PbTiO₃/SrTiO₃ (001) heterostructure band gaps, independently from the number of augmented layers, are always smaller than the PbTiO₃ and SrTiO₃ bulk band gaps. For both PbO and TiO₂-terminated PbTiO₃/SrTiO₃(001) heterostructures, their band gaps are reduced due to the increased number of PbTiO₃ (001) monolayers. The band gaps of PbO-terminated augmented PbTiO₃ (001) films are always larger than those for TiO₂-terminated PbTiO₃ (001) thin films. The only exception is the case of 7-layer PbO-terminated and 8-layer TiO₂-terminated augmented PbTiO₃ (001) thin films, where their band gaps both are equal to 2.99 eV. For each monolayer of the SrTiO₃ (001) substrate, charge magnitudes always are more than several times larger, than for each monolayer in the augmented PbTiO₃ (001) thin film.