En las fronteras de la Materia Condensada

Electron correlation effects in Fe and Ni are analyzed using a first-principles linear combination of atomic orbitals scheme. In our approach, we first use a local orbital functional solution to introduce a Hubbard Hamiltonian without fitting parameters. In a second step, we introduce a many-body solution to this Hamiltonian using a dynamical mean-field approximation. Our analysis shows that magnetism in Fe and Ni is an effect mainly associated with the first Hund's atomic rule. Moreover, we also find important correlation effects in the Fe and Ni spin-polarized density of states. In Fe, the photoemission spectra can be explained using a value of Ueff as large as 4 eV, provided the satellite peaks appearing around 3-5 eV below the Fermi energy are interpreted appropriately. In Ni, correlation effects in the spin-polarized density of states are even larger than in the case of Fe; we will discuss how these effects introduce an important narrowing of the polarized bands in agreement with the experimental evidence.