  By applying density functional theory (DFT) approximations, we present a
first-principles investigation of elastic properties for the experimentally
verified phases of a metallic perovskite LaNiO$_{3}$. In order to improve the
accuracy of calculations, at first we select the most appropriate DFT
approaches according to their performance in reproducing the low-temperature
crystalline structure and the electronic density of states observed for the
bulk LaNiO$_{3}$. Then, we continue with the single-crystal elastic constants
and mechanical stability for the most common rhombohedral as well as
high-temperature cubic and strain-induced monoclinic phases. Together with the
calculated single-crystal elastic constants, the deduced polycrystalline
properties, including bulk, shear, and Young's moduli, Poisson's ratio, Vickers
hardness, sound velocities, Debye temperature, and anisotropy indexes, remedy
the existing gap of knowledge about the elastic and mechanical behaviour of
LaNiO$_{3}$, at least from a theoretical standpoint.
