| Density functional theory is used to study the ground states properties of real materials and the results are used with a model system appropriate to each case to gain accurate physical information about the magnetic and superconducting system. In this work using density functional theory, the magnetic and superconducting properties of some interesting compounds, MnSi, KOs2O6, CuMnSb have been investigated.; MnSi is one of extensively studied materials from the viewpoint of itinerant magnetism. Recently its non-Fermi-liquid nature which can not be understood within the standard theory has been reported. The absence of inversion symmetry in MnSi related to B20 structure is one of the most distinctive features of this compound. The non-symmorphic P213 spacegroup leads to unusual fourfold degenerate states as well as sticking of pairs of bands throughout the entire Brillouin zone surface. CuMnSb is a half-Heusler compound, the first antiferromagnet in the Mn-based class of Heuslers and half-Heuslers that contains several conventional and half metallic ferromagnets, and shows a peculiar stability of its magnetic order in high magnetic fields. Density functional based studies reveal an unusual nature of its unstable paramagnetic state, which for one electron less would be a zero gap semiconductor between two sets of very narrow, topologically separate bands of Mn 3d character. KOs2O6 is a new superconductor with beta-pyrochlore structure, a new variant of the pyrochlore class, suggesting new physics generic to this structural variant. Electronic, magnetic, and dynamical properties of the new superconducting beta-pyrochlore KOs2O6 and related RbOs2O6 and CsOs2O6 compounds are calculated and compared with experiment and contrasted with structurally related spinel pyrochlores. |
