The electronic structure and x-ray magnetic circular dichroism (XMCD) spectra of the Heusler alloy Co 2 FeSi were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments as well as polarization of the electronic states at the Fermi level are analyzed and discussed. The origin of the XMCD spectra in the Co 2 FeSi compound is examined. The calculated results are compared with available experimental data.

The electronic structure of Tm and Sm monochalcogenides, SmB 6 and Yb 4 As 3 is theoretically investigated from the first principles, using the fully relativistic Dirac LMTO band structure method. The electronic structure is obtained using the local spin-density approximation (LSDA), as well as the so-called LSDA+U approach. While the standard LSDA approach is incapable of correctly describing the electronic structure of such materials due to the strong on-site Coulomb repulsion, the LSDA+U approach is remarkably accurate in providing a detailed agreement with experiment for a number of properties.