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Register a new userElectronic structure and non-magnetic character of $delta$-Pu-Am alloys
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Authors
Alexander Shick
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The {em around-mean-field} LSDA+U correlated band theory is applied to investigate the electronic and magnetic structure of $fcc$-Pu-Am alloys. Despite a lattice expansion caused by the Am atoms, neither tendency to 5$f$ localization nor formation of local magnetic moments on Pu atoms in Pu-Am alloys are found. The $5f$-manifolds in the alloys are calculated being very similar to a simple weighted superposition of elemental Pu and Am $5f$-states.
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Electronic structure calculations combining the local-density approximation with an exact diagonalization of the Anderson impurity model show an intermediate 5f^5-5f^6-valence ground state and delocalization of the 5f^5 multiplet of the Pu atom 5f-shell in PuCoIn_5, PuCoGa_5, and delta-Pu. The 5f-local magnetic moment is compensated by a moment formed in the surrounding cloud of conduction electrons. For PuCoGa_5 and delta-Pu the compensation is complete and the Anderson impurity ground state is a singlet. For PuCoIn_5 the compensation is partial and the Pu ground state is magnetic. We suggest that the unconventional d-wave superconductivity is likely mediated by the 5f-states antiferromagnetic fluctuations in PuCoIn_5, and by valence fluctuations in PuCoGa_5.
We present the results of calculations for Pu and Am performed using an implementation of self-consistent relativistic GW method. The key feature of our scheme is to evaluate polarizability and self-energy in real space and Matsubaras time. We compare our GW results with the calculations using local density (LDA) and quasiparticle (QP) approximations and also with scalar-relativistic calculations. By comparing our calculated electronic structures with experimental data, we highlight the importance of both relativistic effects and effects of self-consistency in this GW calculation.
We present a study of the electronic and magnetic properties of the multiple-decker sandwich nanowires ($CP-M$) composed of cyclopentadienyl (CP) rings and 3d transition metal atoms (M=Ti to Ni) using first-principles techniques. We demonstrate using Density Functional Theory that structural relaxation play an important role in determining the magnetic ground-state of the system. Notably, the computed magnetic moment is zero in $CP-Mn$, while in $CP-V$ a significant turn-up in magnetic moment is evidenced. Two compounds show a half-metallic ferromagnetic ground state $CP-Fe/Cr$ with a gap within minority/majority spin channel. In order to study the effect of electronic correlations upon the half-metallic ground states in $CP-Cr$, we introduce a simplified three-bands Hubbard model which is solved within the Variational Cluster Approach. We discuss the results as a function of size of the reference cluster and the strength of average Coulomb $U$ and exchange $J$ parameters. Our results demonstrate that for the range of studied parameters $U=2-4eV$ and $J=0.6-1.2eV$ the half-metallic character is not maintained in the presence of local Coulomb interactions.
We provide a straightforward and numerically efficient procedure to perform local density approximation + Hubbard I (LDA+HIA) calculations, including self-consistency over the charge density, within the full potential linearized augmented plane wave (FP-LAPW) method. This implementation is all-electron, includes spin-orbit interaction, and makes no shape approximations for the charge density. The method is applied to calculate selected heavy actinides in the paramagnetic phase. The electronic structure and spectral properties of Am and Cm metals obtained are in agreement with previous dynamical mean-field theory (LDA+DMFT) calculations and with available experimental data. We point out that the charge density self-consistent LDA+HIA calculations predict the $f$ charge on Bk to exceed the atomic integer $f^8$ value by 0.22.
Density-functional studies of the electronic structures and exchange interaction parameters have been performed for a series of ferromagnetic full Heusler alloys of general formula Co$_2$MnZ (Z = Ga, Si, Ge, Sn), Rh$_2$MnZ (Z = Ge, Sn, Pb), Ni$_2$MnSn, Cu$_2$MnSn and Pd$_2$MnSn, and the connection between the electronic spectra and the magnetic interactions have been studied. Different mechanisms contributing to the exchange coupling are revealed. The band dependence of the exchange parameters, their dependence on volume and valence electron concentration have been thoroughly analyzed within the Green function technique.
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