Optical spectra of rare-earth nickelates

Based on the electronic band structure obtained from first-principles Hubbard corrected U density functional theory (DFT+U) calculations, the optical spectra of yttrium and neodymium nickelates are computed. We show that the results are in fair agreement with available experimental data. We clarify the electronic transitions at the origin of the first two peaks, highlighting the important role of transitions from t2g states neglected in previous models. We discuss the evolution of the optical spectra from small to large rare-earth cations and relate the changes to the electronic band structure.