Basic Research on Electronic Structure Theory in Magnetic Highly-Correlated Electron Systems

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A renewed results related with electronic structure research on some transuranium compounds, especially their Fermi surfaces, were obtained :1.The Fermi surface and the magnetic moment in an antiferromagnet NpRhGa_5 were calculated using a relativistic spin-polarized band theory including an orbital polarization effect. This material has HoGoGa_5-type crystal structure, and the magnetic moments in the ground state are arranged along the [110] direction with a propagation vector q=[0,0,1/2]. It turned out that the shape of the Fermi surface obtained from the calculations well explains the angular dependence of the frequency branches measured by the de Haas-van Alphen (dHvA) effect. Moreover, the magnitude of the magnetic moment at the Np site is in agreement with the observed value by neutron scattering. It became clear from these calculated results to characterize the 5 f electrons of NpRhGa_5 as an itinerant magnetic electron.2.We investigated whether the same character is maintained to a nonmagnetic Np compound without a spin and an orbital degree of freedom. Although almost all Np compounds are magnetic, NpGe_3 is one of a few nonmagnetic compounds. The Fermi surface of NpGe_3 was calculated by relativistic hand theory. The calculated results give a quantitative agreement of the observed dHvA frequency branches. Furthermore, if an enhancement factor estimated by an electronic specific heat coefficient is taken into consideration, we can compare quantitatively the theoretical values with the experimental values for cyclotron effective mass.3.The first observation of a dHvA frequency in a nonmagnetic Pu compound PuIn_3 was successful in the world. The calculated result by a relativistic band theory was able to show an origin of the measured dHvA frequency branch quantitatively. This success suggested that 5 f electrons in nonmagnetic Pu compound also behave as an itinerant electron.