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Abstract: Using a first-principles method, we investigate the electronic structure and optical properties of rhombohedral LaNiO3. The total density of states shows that there is no band gap and bulk LaNiO3 is metallic. There is a strong hybridization between Ni and O orbits near the Fermi level, suggesting that the metallic nature of LaNiO3 mainly originates from Ni 3d states and La atoms have no noticeable contribution to this. The absorption coefficient of LaNiO3 is one order of magnitude less than that of nickel in the lower energy region (0–5 eV), and the interband optical transitions are mainly derived from O 2p and Ni 3d states. In reflectivity spectrum of LaNiO3, there are three main reflectance peaks located at 0 eV, 15.6 eV and 22.9 eV, respectively. In the visible–ultraviolet energy range, the reflectivity of LaNiO3 remarkably decreases with the increasing photon energy and the value is always smaller than that of nickel in the region. [ABSTRACT FROM AUTHOR]