A LDA+U and LDA+DMFT study of uranium mononitride: from nonmagnetic to paramagnetic and ferromagnetic

Abstract

ABSTRACTThe combination of density functional theory in local density approximation and dynamical mean field theory (LDA+DMFT) was employed in a preliminary study of the strong electron correlation effects in a promising nuclear fuel—uranium mononitride (UN). For the ferromagnetic phase, the effective impurity problem arising in the LDA+DMFT [1-3] cycle is solved with the spin-polarized T-matrix fluctuation exchange (SPTF) solver, which includes spin–orbit interactions. Concerning the paramagnetic phase, the disordered local moment (DLM) approach was used, based on both standard local density approximation (LDA) and LDA+U. Basic spectral properties and material properties, such as the spin, orbital and total magnetic moments on U atom were calculated for various values of the Hubbard parameter U with a fixed exchange parameter J. Our main focus was to compare the calculated spectral functions (density of states) for different magnetic phases and different methods to the experimental XPS data [4]. On top of that, the total moments of the paramagnetic and ferromagnetic phases are compared with the measured values by neutron spectroscopy [4, 5].