56 research outputs found
Green function hierarchy for open shells.
No full textIn many systems containing open shell ions, the wave function of the ions cannot be described by a single Slater determinant. This invalidates standard many-body theory and requires the use of nonequilibrium quantum field theory with initial correlations. Quantum group techniques are used here to deal with this combinatorially complex theory. The hierarchy of interacting Green functions for general initial correlations is derived and the case of a system with two-particle correlations is treated in detail
The many-body Green function of degenerate systems
No full text4 pages, 1 figureInternational audienceA rigorous non perturbative adiabatic approximation of the evolution operator in the many-body physics of degenerate systems is derived. This approximation is used to solve the long-standing problem of the choice of the initial states of H0 leading to eigenstates of H0+V for degenerate systems. These initial states are eigenstates of P0 V P0, where P0 is the projection onto a degenerate eigenspace of H0. This result is used to give the proper definition of the Green function, the statistical Green function and the non-equilibrium Green function of degenerate systems. The convergence of these Green functions is established
Multiple-Scattering Theory of Magnetic EXAFS
No full textThis paper discusses various issues of the multiple-scattering theory of magnetic circular dichroism (MCD)
in the x-ray range, especially at the K-edge of 3d transition metals. Using a sernirelativistic expansion of the Dirac Green
function, we show how MCD can be calculated and related to orbital momentum. Moreover, the rigid band model will
be used to relate the high-energy behaviour of MCD to the exchange energy. Finally, we generalise our approach to the
case of orbital polarisation, which was found to be relevant to MCD
4f orbital and spin magnetism in cerium intermetallic compounds studied by magnetic circular x-ray dichroism
No full textGroups of tree-expanded series
No full textAbstractIn [Ch. Brouder, A. Frabetti, Renormalization of QED with planar binary trees, Eur. Phys. J. C 19 (2001) 715–741; Ch. Brouder, A. Frabetti, QED Hopf algebras on planar binary trees, J. Algebra 267 (2003) 298–322] we introduced three Hopf algebras on planar binary trees related to the renormalization of quantum electrodynamics. One of them, the algebra Hα, is commutative, and is therefore the ring of coordinate functions of a proalgebraic group Gα. The other two algebras, He and Hγ, are free non-commutative. Therefore their abelian quotients are the coordinate rings of two proalgebraic groups Ge and Gγ. In this paper we describe explicitly these groups.Using two monoidal structures and a set-operad structure on planar binary trees, we show that these groups can be realized on formal series expanded over trees, and that the group laws are generalizations of the multiplication and the composition of usual series in one variable. Therefore we obtain some new groups of invertible tree-expanded series and of tree-expanded formal diffeomorphisms respectively.The Hopf algebra describing the renormalization of the electric charge corresponds to the subgroup of tree-expanded formal diffeomorphisms formed of the translations, which fix the zero, by some particular tree-expanded series which remind the proper correlation functions in quantum field theory. In turn, the group of tree-expanded formal diffeomorphisms and some of its subgroups give rise to new Hopf algebras on trees.All the constructions are done in a general operad-theoretic setting, and then applied to the specific duplicial operad on trees
Ab Initio Calculation of the Cr K Edge in alpha-Al2O3:Cr3+
No full textThe red color of ruby (-Al2O3:Cr3+) is assigned to transitions between 3d states of the chromium ion. A precise description of the structural and electronic environment of the Cr3+ ion in its slightly distorted octahedral site (C3 symmetry) is needed to understand the cause of the color. We have analysed the Cr K-edge in -Al2O3:Cr3+with a reciprocal space approach that allows the computation of self-consistent spin polarized charge density for large unit cells, beyond the traditional “muffin-tin” approximation. Structural and electronic information is deduced from the calculation
X-ray natural linear dichroism XNLD applied to the determination of relaxations around transition metal impurities in Al2O3
No full textInternational audienc
Life history and ecology of the roundtail chub, Gila robusta, from two streams in the Verde River Basin
No full textabstract: Although not Federally listed as threatened or endangered, the roundtail chub, also a sportfish in Arizona, is nearly extirpated from sections of the Verde and Salt river drainages. The purpose of this investigation, from March 1998 through March 2000, was to describe ecological requirements and population dynamics of roundtail chub. The objectives were to describe species composition, distribution and abundance, quantify habitat selection by different life stages, estimate population size, quantify movement and age and growth, and describe the reproductive capacity of roundtail chub.Technical guidance bulletin ; no. 3Includes bibliographical references (p. 15-16)
Intrinsic charge transfer gap in NiO from Ni K-edge x-ray absorption spectroscopy
No full textInternational audiencePre-edge features in x-ray absorption spectroscopy contain key information about the lowest excited states and thus on the most interesting physical properties of the system. In transition-metal oxides they are particularly structured but extracting physical parameters by comparison with a calculation is not easy due to several computational challenges. By combining core-hole attraction and correlation effects in a first-principles approach, we calculate Ni K-edge x-ray absorption spectra in NiO. We obtain a striking parameter-free agreement with experimental data and show that dipolar pre-edge features above the correlation gap are due to nonlocal excitations largely unaffected by the core hole. We show that in charge transfer insulators, this property can be used to measure the correlation gap and probe the intrinsic position of the upper Hubbard ban
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