Electronic and magnetic properties of quasi-one-dimensional osmium halide OsCl₄

Using ab initio density functional theory, we study the electronic and magnetic properties of the van der Waals chain material OsCl₄. In the nonmagnetic state, a strongly anisotropic band structure was observed, in agreement with its anticipated one-dimensional crystal geometry. Based on Wannier functions, we found that the four electrons of the 5d Os atom form a low-spin S = 1 state, with a large crystal field between the $dxz/yz$ and d_xy orbitals, corresponding to a strong Jahn–Teller distortion (⁠$Q3< 0$⁠). As a consequence, the magnetic properties are mainly contributed by the $dxz/yz$ states. Furthermore, when a Mott gap develops after the introduction of the Hubbard U and Hund coupling J, we found that the staggered spin order is the most likely magnetic state, namely, spins arranged as (↑-↓-↑-↓) with π wavevector along the chain. In addition, the energy differences between various spin states are small, suggesting a weak magnetic exchange coupling along the chain. Our results provide guidance to experimentalists and theorists working on quasi-one-dimensional osmium halides chain materials.