Combining density-functional and dynamical-mean-field theory for ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{TiO}}_3$

The dynamical-mean-field theory combined with the noncrossing approximation is used to set up a scheme to study the electronic structure of strongly correlated electron systems. The noninteracting band structure is obtained from a density-functional calculation within the local-density approximation. With this method the doped Mott insulator ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Ti}\mathrm{}\mathrm{O}}_3$ is studied. Starting from first-principle calculations for a cubic and an orthorhombic system we determine the one-particle spectrum. Both one-particle spectra show a lower Hubbard band (seen as $d^1\to d^0$ transitions in photoemission experiments) and a quasiparticle resonance near the Fermi energy and the upper Hubbard band ${(d}^1\to d^2$ transitions in an inverse photoemission experiment). The upper Hubbard band develops a multipeak structure, a consequence of the consideration of all local two-particle correlations, which leads to the full multiplet structure in the atomic limit. The calculation for the orthorhombic system shows qualitative good agreement when compared with experimental photoemission spectra.