Electronic structures, magnetism, and phonon spectra in the metallic cubic perovskite BaOsO3

By using ab initio calculations, we investigated a cubic perovskite BaOsO3 and a few related compounds that have been synthesized recently and formally have a metallic d(4) configuration. In BaOsO3, which shows obvious three-dimensional fermiology, a nonmagnetism is induced by a large spin-orbit coupling (SOC), which is precisely equal to an exchange splitting similar to 0.4 eV of the t(2g) manifold. However, the inclusion of on-site Coulomb repulsion as small as U-c approximate to 1.2 eV, only 1/3 of the t(2g) bandwidth, leads to the emergence of a spin-ordered moment, indicating that this system is on the verge of magnetism. In contrast to BaOsO3, our calculations suggest that the ground state of an orthorhombic CaOsO3 is a magnetically ordered state due to the reduction of the strength of SOC (about a half of that of BaOsO3) driven by the structure distortion, although the magnetization energy is only a few tenths of meV. Furthermore, in the cubic BaOsO3 and BaRuO3, our full-phonon calculations show several unstable modes, requiring further research.