LDA+U Study on Fully Relaxed LaTiO3 and (SrTiO3)m(LaTiO3)n Superlattice Structures

Using LDA+U (where LDA stands for local-density-approximation and U for on-site coulomb energy) method, we study the structural and electronic properties of LaTiO3 and (SrTiO3)m(LaTiO3)n superlattice structures. Lattice vectors, as well as ionic positions, are relaxed to minimize the LDA+U energy functional. We find that the inclusion of the U term increases the lattice parameters and leads to larger distortions of oxygen octahedra in LaTiO3 and that the overall agreement with experiment is improved compared to LDA results. In the superlattice, we find that octahedral distortions around the La layer lower the total energy. The ionic relaxations, especially those of Ti atoms near the La layer, affect the spatial distribution of doped electrons, leading to a broader charge profile than the case without ionic relaxation. The corresponding Ti3+ profile is in good agreement with the electron-energy-loss spectroscopy data.