Coulomb-U and magnetic moment collapse in δ-Pu

– The around-the-mean-field version of the LDA+Umethod is applied to investigate electron correlation effects in δ-Pu. It yields a non-magnetic ground state of δ−Pu, and provides a good agreement with experimental equilibrium volume, bulk modulus and explains important features of the photoelectron spectra. Plutonium is probably the most intricate element from the point of view of condensed matter physics. It exhibits six allotropic modifications at ambient pressure, some of them of very low symmetry (monoclinic), and there is little doubt that the anomalous behaviour is related to the 5f electronic states, being at the borderline between the localized, nonbonding, behaviour and the bonding situation of electronic bands. One can preconceive that at the cross-over regime, several states with very different degree of 5f delocalization can be nearly degenerated in energy. The most thoroughly studied phases are α−Pu (monoclinic) and δ−Pu (fcc). The latter is stable between 592 and 724 K, but can be stabilized down to T = 0 K by various dopants. This phase has the largest volume (by 20% higher than α−Pu) (for overview see Ref. [1] and references therein). The atomic volume is an important indicator of the situation of the 5f -electronic states. Withdrawing of the 5f states from the bonding and confining them in the ionic core leads to a significant volume expansion. On the plot of atomic volumes of elements, Pu (α) represents a continuation of light actinides, with the decreasing branch resembling the parabolic behavior of transition metals. On the other hand, heavy actinides, starting with Am (Z = 95), display higher volume, following a weakly decreasing volume of lanthanides, characterized by nonbonding 4f states. δ−Pu, being half way between the volume of α−Pu and Am, represents therefore generally the cross-over regime, where electron-electron correlations play a prominent role. Ab-initio electron energy calculations based on the Density Functional Theory (DFT) in the Local Density (LDA) or Generalized Gradient (GGA) approximations account generally well for basic properties of metallic systems. Numerous variants of this successful paradigma were applied to Pu phases. The most conspicuous failure is the case of δ−Pu calculations which