Correlation effects in electronic structure of PuCoGa5

We report on results of the first realistic electronic structure calculations of the Pu-based PuCoGa5 superconductor based on the dynamical mean field theory. We find that dynamical correlations due to the local Coulomb interaction between Pu f-electrons lead to substantial modification of the electronic structure with a narrow peak being formed in vicinity of the Fermi energy, in agreement with the experimental photoemission spectra, and in contrast with the recent calculations within the LDA+U method, where only static electronic correlations have been included. Both Pu and Co contribute in equal footing to the narrow peak on the density of states at the Fermi level, the Co partial density of states being prominently affected by electronic correlations on the Pu sites. The k-resolved spectral density is calculated and the theoretical spectral function resolved extended Van Hove singularity near the Fermi energy. This singularity may lead to enchancement of the magnetic susceptebility and favour d-wave superconductivity

On some geometric features of the Kramer interior solution for a rotating perfect fluid

Geometric features (including convexity properties) of an exact interior gravitational field due to a self-gravitating axisymmetric body of perfect fluid in stationary, rigid rotation are studied. In spite of the seemingly non-Newtonian features of the bounding surface for some rotation rates, we show, by means of a detailed analysis of the three-dimensional spatial geodesics, that the standard Newtonian convexity properties do hold. A central role is played by a family of geodesics that are introduced here, and provide a generalization of the Newtonian straight lines parallel to the axis of rotation.Comment: LaTeX, 15 pages with 4 Poscript figures. To be published in Classical and Quantum Gravit

Electronic structure and spectral properties of Am, Cm and Bk: Charge density self-consistent LDA+HIA calculations in FP-LAPW basis

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.Comment: 8 pages, 1 figur

Hydrogen on graphene: Electronic structure, total energy, structural distortions, and magnetism from first-principles calculations

Density functional calculations of electronic structure, total energy, structural distortions, and magnetism for hydrogenated single-layer, bilayer, and multi-layer graphene are performed. It is found that hydrogen-induced magnetism can survives only at very low concentrations of hydrogen (single-atom regime) whereas hydrogen pairs with optimized structure are usually nonmagnetic. Chemisorption energy as a function of hydrogen concentration is calculated, as well as energy barriers for hydrogen binding and release. The results confirm that graphene can be perspective material for hydrogen storage. Difference between hydrogenation of graphene, nanotubes, and bulk graphite is discussed.Comment: 8 pages 8 figures (accepted to Phys. Rev. B

An dynamical-mean-field-theory investigation of specific heat and electronic structure of α\alpha and δ\delta-plutonium

We have carried out a comparative study of the electronic specific heat and electronic structure of $\alpha$ and $\delta$-plutonium using dynmical mean field theory (DMFT). We use the perturbative T-matrix and fluctuating exchange (T-matrix FLEX) as a quantum impurity solver. We considered two different physical pictures of plutonoium. In the first, $5{f^5}+$, the perturbative treatment of electronic correlations has been carried out around the non-magnetic (LDA) Hamiltonian, which results in an f occupation around a bit above $n_f = 5$. In the second, $5{f^6}-$, plutonium is viewed as being close to an $5{f^6}$ configuration, and perturbation theory is carried out around the (LDA+U) starting point bit below $n_f = 6$. In the latter case the electronic specific heat coefficient $\gamma$ attains a smaller value in $\gamma$-Pu than in $\alpha$-Pu, in contradiction to experiment, while in the former case our calculations reproduce the experimentally observed large increase of $\gamma$ in $\delta$-Pu as compared to the $\alpha$ phase. This enhancement of the electronic specific heat coefficient in $\delta$-Pu is due to strong electronic correlations present in this phase, which cause a substantial increase of the electronic effective mass, and high density of states at $E_F$. The densities of states of $\alpha$ and $\delta$-plutonium obtained starting from the open-shell configuration are also in good agreement with the experimental photoemission spectra.Comment: 6 pages, 3 figure

Existence of axially symmetric static solutions of the Einstein-Vlasov system

We prove the existence of static, asymptotically flat non-vacuum spacetimes with axial symmetry where the matter is modeled as a collisionless gas. The axially symmetric solutions of the resulting Einstein-Vlasov system are obtained via the implicit function theorem by perturbing off a suitable spherically symmetric steady state of the Vlasov-Poisson system.Comment: 32 page

Multiple scattering formalism for correlated systems: A KKR+DMFT approach

We present a charge and self-energy self-consistent computational scheme for correlated systems based on the Korringa-Kohn-Rostoker (KKR) multiple scattering theory with the many-body effects described by the means of dynamical mean field theory (DMFT). The corresponding local multi-orbital and energy dependent self-energy is included into the set of radial differential equations for the single-site wave functions. The KKR Green's function is written in terms of the multiple scattering path operator, the later one being evaluated using the single-site solution for the $t$-matrix that in turn is determined by the wave functions. An appealing feature of this approach is that it allows to consider local quantum and disorder fluctuations on the same footing. Within the Coherent Potential Approximation (CPA) the correlated atoms are placed into a combined effective medium determined by the dynamical mean field theory (DMFT) self-consistency condition. Results of corresponding calculations for pure Fe, Ni and Fe$_{x}$Ni$_{1-x}$ alloys are presented.Comment: 25 pages, 5 fig. acepted PR

Aligning flexibility with uncertainty in software development arrangements through a contractual typology

Purpose The purpose of this study is to identify a typology of procurement contracts in the context of software development projects that allows firms to align design flexibility with design uncertainty at the project level. The theoretical lenses of contract theory and software engineering are used to explain why the five archetypes in the proposed typology provide gradually increasing levels of design flexibility and to develop hypotheses about the associations between design flexibility and a set of project cost dimensions. Design/methodology/approach The hypotheses are tested with objective contractual data from 270 software development contracts entered into by a leading international bank over a period of three years. Findings Data analysis confirms the existence of the proposed typology and shows that design flexibility is negatively associated with control and positively associated with coordination, trust, duration and price. Research limitations/implications Although the findings are based on the contracting practices of a single, albeit sophisticated, organization, they shed light on the ability of firms to align flexibility with uncertainty at the onset of new projects by taking advantage of nuanced contractual mechanisms to produce a broader set of contractual archetypes. Originality/value This paper is the first in the outsourcing literature to analyze a nuanced contractual typology in software development projects through the perspectives of both contract theory and software engineering