Ab initio investigations of electron correlation effect and phonon dynamics of orthorhombic uranium

Abstract

We have performed first principles calculations for the electronic, dynamical, and thermodynamic properties of a-U using the projector augmented wave (PAW) method. The optimized lattice parameters, equilibrium volume, atomic energy, bulk modulus, and its pressure derivative are close to the experimental data and other calculations. To evaluate the strong on-site Coulomb repulsion among the localized uranium 5f electrons, the generalized gradient approximation (GGA)þU formalism have been adopted. It is shown that the total DOS at the Fermi energy level mainly comes from the contribution of narrow f band, the electron correlation effect is small for metallic bands of uranium. In particular, the phonon spectrum of a-U is calculated within density functional perturbation theory (DFPT) as well as the small displacement method, the coincidence between our calculations and Crummett et al.'s inelastic neutron scattering measurements indicates that both phonon methods based on PAW scheme are reasonable to capture the anomalous phonon properties of a-U. The calculated dynamical properties of uranium under pressure suggest that Cmcm uranium should be stabilized dynamically at least up to 100 GPa, which accords with X-ray diffraction experimental results of Le Bihan et al. The thermodynamic functions of a-U under high temperature and high pressure are also obtained further.