title: The first-principles treatment of the electron-correlation and spin-orbital effects in uranium mononitride nuclear fuels.
abstract: The DFT+U calculations were employed in a detailed study of the strong electron correlation effects in a promising nuclear fuel-uranium mononitride (UN). A simple method for solving the multiple minima problem in DFT+U simulations and insure obtaining the correct ground state is suggested and applied. The crucial role of spin-orbit interactions in reproduction of the U atom total magnetic moment is demonstrated. Basic material properties (the lattice constants, the spin- and total magnetic moments on U atoms, the magnetic ordering, and the density of states) were calculated varying the Hubbard U-parameter. By varying the tetragonal unit cell distortion, the meta-stable states have been carefully identified and analyzed. The difference in the magnetic and structural properties obtained for the meta-stable and ground states is discussed. The optimal effective Hubbard parameter U(eff) = 1.85 eV reproduces correctly the UN anti-ferromagnetic ordering, and only slightly overestimates the experimental total magnetic moment of the U atom and the unit cell volume.
authors.affiliation: European Commission, Joint Research Centre, Institute for Transuranim Elements, Karlsruhe, Germany. gryaznov@mail.com
authors.forename: Denis
authors.initials: D
authors.lastname: Gryaznov
authors.forename: Eugene
authors.initials: E
authors.lastname: Heifets
authors.forename: Eugene
authors.initials: E
authors.lastname: Kotomin