Investigation on the electronic structure of the actinide dioxide by the relativistic band calculation incorporating the effect of CEF potential.

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The main purposes of this project were to study related actinide dioxide of strongly correlated electron systems, and to development the relativistic band calculation based on the effect of crystalline electric field potential. The electronic structure of AnO_2(An=U, Np, Pu, Am) is simply understood with the use of an appropriate band-structure calculation technique in a local density approximation (LDA), but in actuality, it is not so easy to reproduce correctly semiconducting behavior in the LDA. Since in the fluorite structure of actinide dioxide with cubic symmetry, Γ_7 level should be lower than Γ_8 one in the LDA approach, we do not obtain the Γ_1 singlet ground state for AnO_2, when we simply accommodate four f electrons in such a level scheme. In order to improve the situation, we proposed a new idea to consider explicitly the effect of crystalline electric field (CEF) potential in the band-structure calculation with the LDA. The relativistic band calculation program was developed by the combination of the RLAPW and the CEF method.The method was applied to actinide dioxides. Thus our strategy to study the actinide dioxide in strongly correlated electron systems is shown to be useful and has been developed.