Dual nature of the ferroelectric and metallic state in LiOsO3

Using density functional theory we investigate the lattice instability and electronic structure of recently discovered ferroelectric metal LiOsO3. We show that the ferroelectric-like lattice instability is related to the Li-O distortion modes while the Os-O displacements change the d-p hybridization as in common ferroelectric insulators. Within the manifold of the d orbitals, a dual behavior emerges. In the ferroelectric transition the empty e(g) orbitals change their hybridization with the oxygen p orbitals, while the t(2g) orbitals are responsible for the metallic response. Interestingly, these orbitals are nominally half filled by three electrons, a configuration which suffers from strong correlation effects even for moderate values of the screened Coulomb interaction.