Electronic structure and resonant inelastic x-ray scattering in Ta₂NiSe₅

We study the electronic structure of Ta₂NiSe₅in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the TaL₃edge. We also investigate the electronic properties of Ta₂NiSe₅within the density-functional theory (DFT) using the generalized gradient approximation in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. While ARPES, dc transport, and optical measurements indicate that Ta₂NiSe₅is a small band-gap semiconductor, DFT gives a metallic nonmagnetic solution in Ta₂NiSe₅. To obtain the semiconducting ground state in Ta₂NiSe₅we use a self-interaction-like correction procedure by introducing an orbital-dependent potentialV_linto the Hamiltonian. We investigate theoretically the x-ray absorption spectroscopy and RIXS spectra at the Ni and TaL₃edges and analyze the spectra in terms of interband transitions. We also investigate the RIXS spectra as a function of momentum transfer vectorQand incident photon energy.