First-principles investigation of the electronic and magnetic properties of quasi-one-dimensional MoBr₃

We investigate the electronic and magnetic properties of molybdenum tribromide, MoBr₃ using first-principles density functional theory. MoBr₃ consists of weakly coupled one-dimensional chains in which each Mo³⁺ ion is surrounded by a Br octahedron, face-sharing with neighboring octahedra. The ground state structure exhibits dimerization of Mo-Mo pairs with alternating short and long bonds, consistent with the experimental report. We find an insulating ground state with antiferromagnetic ordering having a magnetic moment of 1.8 µ_B on each Mo atom, smaller than the fully polarized value of 3 µ_B from the d³ filling of Mo, indicating orbital-dependent hybridization, which reduces the magnetic moment of Mo- d_z² orbitals extending along the dimer direction. Comparison of the electronic structures of dimerized and non-dimerized antiferromagnetic phases shows that the dimerized phase is preferred. Energy lowering by a bonding-antibonding splitting of the Mo-d_z² bands from dimerization is larger than increasing the magnetic moment without dimerization, indicating the dominant inter-orbital hopping exceeding the Hund coupling for the d_z² orbitals. We identify the interplay between on-site and inter-site interaction in the system with nominal Mo-d³ filling leads to orbital-dependent suppression of the magnetic moments, manifested from the quasi one-dimensional geometry.