First-principles investigation of the complex lattice, charge, orbital, and spin structures in the spinel CuIr₂S₄

The CuIr₂S₄ thiospinel undergoes a metal-insulator transition at 230K on cooling accompanied by very large variations in the Ir-Ir bond lengths and the loss of localized magnetic moments. This phenomenon has been interpreted in terms of a unique octamer model and orbitally driven one-dimensional Peierls transition. Here we report systematic first-principles studies of the crystal structures, electronic band structures, and phonon spectra of CuIr₂S₄, as well as the effects of electron-phonon, electron-electron, and spin-orbit interactions. Wannier function analysis is used to derive the effective low-energy Hamiltonian. Our results suggest a new way to understand this material.