  Based on the electronic band structure obtained from first principles DFT
calculations, the opticalspectra of yttrium and neodymium nickelates are
computed. We show that the results are in fairagreement with available
experimental data. We clarify the electronic transitions at the origin of
thefirst two peaks, highlighting the important role of transitions from t2g
states neglected in previousmodels. We discuss the evolution of the optical
spectra from small to large rare-earth cations andrelate the changes to the
electronic band structure.
