Electronic structure and optical properties of Am monopnictides

The ground-state and optical properties of the americium monopnictides, AmX (X=N, P, As, Sb, and Bi) are investigated theoretically on the basis of first-principles electronic structure calculations, employing the local density approximation (LDA) as well as the LDA+U approach. The LDA predicts pseudogap-like behavior in AmN and narrow gap (39-78 meV) semiconducting behavior in AmP to AmBi at ambient conditions. The LDA+U calculations predict semiconducting behavior with a real gap of 192 meV for AmN and a pseudogap in AmP to AmBi. The computed semiconducting or pseudogap character is in fine agreement with the first photoemission experiments performed on AmN and AmSb films by Gouder [preceding paper, Phys. Rev. B 72, 115122 (2005)]. This property is shown to result from the strong Am spin-orbit interaction, the Coulomb repulsion, and the particular p-d-f hybridizations. The calculated equilibrium lattice constants obtained for the AmX series using the LDA+U technique are in good agreement with available experimental data. Also, the binding energies of the 5fs computed with the LDA+U approach correspond well to 5f binding energies deduced from the photoemission spectra measured by Gouder The high, temperature-independent paramagnetic susceptibilities of the AmX are successfully explained by a Van Vleck mechanism. A pressure-induced valence transition at high pressure is predicted for AmN.