Research on one particle picture near the localized-delocalized transition in the strongly correlated f-electron system

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The program code for electronic structure calculations with an FLAPW and an LDA+U method has been developed for strongly correlated electron systems, to treat the magnetic states. Then electronic structures are obtained for CeRu_2Si_2 in the region of meta magnetic transition, and for CeIn_3 under pressures. It revels that the results strongly depend on the magnitude of U and the applied magnetic field, so such the dependence should be investigated more. Now the electric field gradients(EFG) can be obtained even by the LDA+U method. It has been revealed that the asymmetry parameters strongly depend on the configurations for multi f states even for the singlet state under a cubic symmetry. This indicates that the EFG, directly compared with NQR frequencies, obtains important information to determine the configuration of the multi f electrons. On the other hand, the effective model for the crystalline electric filed (CEF) for the j-j coupling scheme has been developed, to solve the problem that the multi f electron states split by the CEF potential in the j-j coupling model are not compatible, even qualitatively, with those obtained in the LS coupling scheme. As well known, the non-Kramers doublet cannot be obtained for f^2 state in the j-j coupling scheme, because of no 6^<th> order term appearing in j=5/2 space. We have proposed that the term in the order of 1/lambda must be included in the CEF calculations, where lambda is the strength of the spin-orbit interactions, and assumed to be infinite in the j-j coupling scheme. This means that the contributions from j=7/2 are taken into account in the j-j coupling scheme. Then it is shown the results in our effective j-j model quantitatively agree with those in the LS coupling scheme, even for the T_h symmetry in filled skutterydutes.