Ab initiostudy of the factors affecting the ground state of rare-earth nickelates

We have used first-principles methods to investigate the factors that control the ground state of rare-earth nickelates, studying in detail the case of NdNiO₃. Our results suggest a complex phase diagram, with the bulk compounds standing on the edge of various instabilities that can be triggered by both electronic (e.g., changes in the Coulomb repulsion) and structural (e.g., epitaxial mismatch) means. In particular, we reveal that several phase transitions can be induced by epitaxial strain in thin films and predict that a continuous transformation between insulating spin-density-wave- and metallic spin-spiral-like solutions occurs at moderate values of the in-plane mismatch. Our results provide a coherent picture of structural and electronic effects in nickelates and have implications for current experimental and theoretical work on these compounds.