Dynamical Mean-Field Theory on the Real-Frequency Axis: p-d Hybridizations and Atomic Physics in SrMnO₃

We investigate the electronic structure of SrMnO$_3$ with Density Functional Theory (DFT) plus Dynamical Mean-Field Theory (DMFT). Within this scheme the selection of the correlated subspace and the construction of the corresponding Wannier functions is a crucial step. Due to the crystal field splitting of the Mn-$3d$ orbitals and their separation from the O-2$p$ bands, SrMnO$_3$ is a material where on first sight a 3-band $d$-only model should be sufficient. However, in the present work we demonstrate that the resulting spectrum is considerably influenced by the number of correlated orbitals and the number of bands included in the Wannier function construction. For example, in a $d$-$dp$ model we observe a splitting of the \tg lower Hubbard band into a more complex spectral structure, not observable in $d$-only models. To illustrate these high-frequency differences we employ the recently developed Fork Tensor Product State (FTPS) impurity solver, as it provides the necessary spectral resolution on the real-frequency axis. We find that the spectral structure of a 5-band $d$-$dp$ model is in good agreement with PES and XAS experiments. Our results demonstrate that the FTPS solver is capable of performing full 5-band DMFT calculations directly on the real-frequency axis.