In order to understand the role of hole doping on electronic structure, phase stability and magnetic properties of ${\mathrm{LaCoO}}_3$ generalized-gradient-corrected, relativistic first-principles full-potential density functional calculations have been performed for ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ as a function of x, using the supercell approach as well as the virtual crystal approximation (VCA). It has been shown that the rhombohedral distortion is stabilizing the nonmagnetic (i.e., diamagnetic or paramagnetic) ground state in ${\mathrm{LaCoO}}_3.$ Spin-polarized calculation on the hypothetical cubic perovskite phase of ${\mathrm{LaCoO}}_3$ shows that the ferromagnetic phase is lower in energy than the corresponding nonmagnetic phase. The analysis of the electronic structures show that a Peierls-Jahn-Teller-like instability arises in the ferromagnetic cubic phase and leads to the rhombohedral distortion in ${\mathrm{LaCoO}}_3.$ The calculated magnetic moment for ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ as a function of Sr substitution is found to be in very good agreement with recent neutron scattering measurements. We have successfully explained the hole-doping induced, nonmagnetic-to-ferromagnetic transition as well as the rhombohedral-to-cubic structural transition as a function of Sr substitution in ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3.$ Due to the failure of the density functional theory to predict the semiconducting nature of ${\mathrm{LaCoO}}_3,$ we are unable to explain the experimentally observed semiconductor-to-metal transition in ${\mathrm{LaCoO}}_3$ by Sr substitution. The origin of the ferromagnetism in ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ has been explained through itinerant-band ferromagnetism.

• Received 23 June 1999

DOI:https://doi.org/10.1103/PhysRevB.60.16423