Change of Fermi surface topology in CeRu₂Si₂ studied by LSDA+U method

The detailed electronic structures of CeRu₂Si₂ have been investigated for a nonmagnetic state and a magnetic state under magnetic fields by an LSDA+U method. It is found that the Si position in the crystal structure is an essential parameter to reproduce precise topology of the experimentally determined Fermi surfaces of non-f reference LaRu ₂Si₂. As for CeRu₂Si₂, the LDA calculation fails to predict the nonmagnetic ground state, which is experimentally reported to be mainly occupied by |j = 5/2, j_z = ±5/2) orbitals, and the Fermi surfaces. The nonmagnetic case solution of LSDA+U method greatly improves the electronic structure in the nonmagnetic CeRu₂Si₂. An LSDA+U method is also applied to investigate the electronic structure under applied magnetic fields, then the change of the so-called large Fermi surfaces to small Fermi surfaces is successfully described.