Variation of theLDA+Umethod appropriate tof-state localization: Application to magneto-optical properties

Abstract

A variation of the local density approximation (LDA)ϩU method, appropriate for application to cerium f-state localization, and its implementation within a full-potential linear muffin-tin orbital method is described. The method, functionally similar to the self-interaction-corrected-pseudopotential method, is applied to a calculation of the optical conductivity and ground-state magnetic moments of the compounds CeSb and CeTe. We also briefly discuss application of the method to the equilibrium volume of fcc plutonium, giving about 94% of the experimental volume, a significant improvement over LDA results. We find that the off-diagonal conductivity of CeSb ͑which gives the magneto-optical behavior͒ agrees well with experiment, suggesting that the method correctly captures essential aspects of the electron correlation. The optical conductivity and groundstate moment of CeTe, however, show poorer agreement with experiment than for CeSb.The widely used LDA ͑local-density approximation͒ and LSDA ͑local spin density approximation͒ methods for calculating electronic structure fail for highly correlated electron systems, and a number of modifications of these techniques have been proposed to allow their application to such materials. Such modifications include the LDAϩU method, [1][2][3][4] self-interaction-corrected 5-8 ͑SIC͒ calculations, and combination of LDA calculated parameters with model Hamiltonians.9 Here we investigate a simple variation on the LDAϩU approach, appropriate for application to Ce and Ce compounds, and to some extent to actinide systems. We specifically examine the resulting optical conductivity and ground-state moments for CeSb and CeTe, and briefly indicate results for the atomic volume of fcc Pu.The LDAϩU technique, 1 designed for systems in which a set of orbitals ͑typically d or f states͒ is highly localized, modifies the LDA energy functional by subtracting the LDA ''f-f'' interactions, replacing them with on-site, atomiclike interactions, using a Hartree-Fock form for the electronelectron interactions. This modified energy functional has explicit orbital dependence, and consequently the effective one-electron potential has an orbital dependence, where the addition to the effective potential consists of spatially constant matrix elements, V m,m Ј , between f ͑or d͒ basis functions. The eigenstates of the modified one-electron Hamiltonian are then obtained. The one-electron eigenstates are not localized functions, but remain Bloch states. The primary effect is that the energy eigenvalues of the occupied f states are forced lower in energy ͑by roughly U/2͒, while unoccupied f states are raised in energy, thus, for example, providing the gap in Mott-Hubbard insulators.For cerium systems, where the Ce localizes at most one f electron per site, this process represents a self-interaction correction, since the LDA self-interaction is subtracted, and the Hartree-Fock self-interaction is zero. In the SIC method ͑in atoms, for example 5 ͒, the explicit subtraction of orbital self-interaction also low...

Spectral properties ofδ-plutonium: Sensitivity to5foccupancy

“…14 Several research groups 15,16,17 have applied the LDA+U method to include more f -f correlation energy. By adjusting the on-site Coulomb repulsion energy (U ) appropriately, it has been possible to fit to the experimental δ-phase volume.…”

Development of magnetism in strongly correlated cerium systems: Non-Kondo mechanism for moment collapse

“…LDAϩU calculations for the heavier systems CeSb and CeTe increase the magnetic moment to 2.2 B and 1.4 B , respectively. 22 Similarly, we find that the LDAϩU method increases the magnetic moment for the lighter, more delocalized systems, CeP and CeS to 2.0 B and 1.9 B , respectively. Thus, the LDAϩU method enhances the magnetic moment across the entire series and fails to predict the trend of magnetic properties.…”

“…Finally, we predict the experimentally observed change of the ground-state magnetic structure from the ͗001͘ AF-IA ͑↑↑↓↓͒ in CeBi and CeSb to the ͗001͘ AF-I ͑↑↓͒ in CeAs and CeP. In sharp contrast, the second, ab initio method, based on density functional theory within the local density approximation ͑LDA͒, 20,21 and on the LDAϩU scheme 22 fail to predict, even qualitatively, the trend of magnetism in this series of strongly correlated electron systems.…”

“…22 The crystalline field, neglected in the previous calculations, 4,5 is expected to affect the magnetic behavior considerably, if it is large. The experimentally observed crystal-field splitting is ⌬ CF * ϭ⌬ CF ϩ␦⌬ CF , where ⌬ CF is the ''bare'' CF splitting and ␦⌬ CF is the hybridization-induced CF splitting.…”

First-principles study of the Kondo physics of a single Pu impurity in a Th host

“…These unusual physical and mechanical properties 3 are believed to be caused by the itinerant-tolocalized crossover of 5f electronic orbitals 4 . Band-structure calculations within the local density approximation (LDA) fail to predict the equilibrium volume of the nonmagnetic δ-phase of Pu 8,9 ; while the LDA+U calculations gives the experimental δ-phase volume with an appropriate value of U but also indicates an instability toward an antiferromagnetic ground state [10][11][12] . Later LDA+U calculations [13][14][15][16] that included spinorbit coupling (SOC) suggested that the magnetism could be naturally quenched and that the correct δ-phase volume could be obtained if the Pu atom is in a closed-shell Pu 5f 6 configuration,.…”