Electronic structure of CrAs and FeAs

As in a recent study for MnAs a two centre tight binding model consisting of itinerant metal d-states hybridizing with non-metal p-states was applied for CrAs and FeAs to calculate unpolarized and spin polarized local densities of states, ferromagnetic moments and band energies. The factor for the change of the d-band width relative to MnAs was estimated to be 1.3 for CrAs and 0.8 for FeAs. The self-consistent separation of the p- and d-band centres amounts to -1.3 eV for CrAs and -0.5 eV for FeAs providing a charge transfer of 0.8 and 0.6 electrons from the metal to the As atoms, correspondingly. One B8 1 structure and two B31 structures according to low and high temperature phases were studied for each compound. For CrAs self-consistent magnetic moments of 1.58 and 1.2μ B were obtained, respectively. For FeAs no ferromagnetic moment could be stabilized unless the d-band width was substantially reduced. The results are discussed with respect to MnAs. The model is able to reproduce the increase and breakdown of the magnetic moment for the series CrAs-MnAs-FeAs. Furthermore, the correct structural trend B31-B8 1 -B31 is obtained if the band energy differences are corrected by a constant of 0.3 eV. This correction is attributed to the failure of the model to provide absolute differences of total energies.