ELECTRONIC-STRUCTURE AND FERMI-SURFACE OF LARU2SI2

The energy band structure and the Fermi surface are calculated for LaRu2Si2 with a body-centered tetragonal crystal structure by a self-consistent relativistic symmetrized APW method with the exchange and correlation potential in the local-density approximation. The main Fermi surface is an extraordinarily large, closed hole sheet with a cross-sectional area exceeding the size of the Brillouin zone itself. There are additionally small hole and electron sheets, all of which have no open orbit. The Fermi surface topology is consistent with the experimental result for the high-field transverse magnetoresistance. By these Fermi surfaces, both the magnitude and the angular dependence of the frequency branches of the de Haas-van Alphen effect measured recently by Onuki et al. can be explained reasonably well. The Fermi surfaces of the related heavy-electron-compound CeRu2Si2 and ferromagnetic compound CeRu2Ge2 are discussed briefly.