Electronic structure Hamiltonians Magnetic moments Magnetic properties article Approximation theory Cobalt Magnetism Electronic properties Multilayers CALCULOS DE PRIMEROS PRINCIPIOS ELECTRONIC PROPERTIES Granular materials Magnetoresistance PROPIEDADES ELECTRONICAS Transition metals energy Ab initio calculations Band structure Band structure calculations Calculations Electric conductivity Granular alloys Hartree-Fock approximation Magnetic couplings Magnetic materials Nanostructured materials calculation electron magnetism