243 research outputs found
Time-Dependent Gutzwiller Theory for Multiband Hubbard Models
Based on the variational Gutzwiller theory, we present a method for the
computation of response functions for multiband Hubbard models with general
local Coulomb interactions. The improvement over the conventional random-phase
approximation is exemplified for an infinite-dimensional two-band Hubbard model
where the incorporation of the local multiplet-structure leads to a much larger
sensitivity of ferromagnetism on the Hund coupling. Our method can be
implemented into LDA+Gutzwiller schemes and will therefore be an important tool
for the computation of response functions for strongly correlated materials.Comment: 4 pages, 3 figure
Coexistence of spin-triplet superconductivity with magnetism within a single mechanism for orbitally degenerate correlated electrons: Statistically-consistent Gutzwiller approximation
An orbitally degenerate two-band Hubbard model is analyzed with inclusion of
the Hund's rule induced spin-triplet paired states and their coexistence with
magnetic ordering. The so-called statistically consistent Gutzwiller
approximation (SGA) has been applied to the case of a square lattice. The
superconducting gaps, the magnetic moment, and the free energy are analyzed as
a function of the Hund's rule coupling strength and the band filling. Also, the
influence of the intersite hybridization on the stability of paired phases is
discussed. In order to examine the effect of correlations the results are
compared with those calculated earlier within the Hartree-Fock (HF)
approximation combined with the Bardeen-Cooper-Schrieffer (BCS) approach.
Significant differences between the two used methods (HF+BCS vs. SGA+real-space
pairing) appear in the stability regions of the considered phases. Our results
supplement the analysis of this canonical model used widely in the discussions
of pure magnetic phases with the detailed elaboration of the stability of the
spin-triplet superconducting states and the coexistent magnetic-superconducting
states. At the end, we briefly discuss qualitatively the factors that need to
be included for a detailed quantitative comparison with the corresponding
experimental results
Random phase approximation for multi-band Hubbard models
We derive the random-phase approximation for spin excitations in general
multi-band Hubbard models, starting from a collinear ferromagnetic Hartree-Fock
ground state. The results are compared with those of a recently introduced
variational many-body approach to spin-waves in itinerant ferromagnets. As we
exemplify for Hubbard models with one and two bands, the two approaches lead to
qualitatively different results. The discrepancies can be traced back to the
fact that the Hartree-Fock theory fails to describe properly the local moments
which naturally arise in a correlated-electron theory.Comment: 25 pages, 2 figure
LDA+Gutzwiller Method for Correlated Electron Systems: Formalism and Its Applications
We introduce in detail our newly developed \textit{ab initio} LDA+Gutzwiller
method, in which the Gutzwiller variational approach is naturally incorporated
with the density functional theory (DFT) through the "Gutzwiller density
functional theory (GDFT)" (which is a generalization of original Kohn-Sham
formalism). This method can be used for ground state determination of electron
systems ranging from weakly correlated metal to strongly correlated insulators
with long-range ordering. We will show that its quality for ground state is as
high as that by dynamic mean field theory (DMFT), and yet it is computationally
much cheaper. In additions, the method is fully variational, the charge-density
self-consistency can be naturally achieved, and the quantities, such as total
energy, linear response, can be accurately obtained similar to LDA-type
calculations. Applications on several typical systems are presented, and the
characteristic aspects of this new method are clarified. The obtained results
using LDA+Gutzwiller are in better agreement with existing experiments,
suggesting significant improvements over LDA or LDA+U.Comment: 20 pages, 11 figure
Mean-field phase diagram of interacting e_g electrons
We investigate the magnetic phase diagram of the two-dimensional model for
e_g electrons which describes layered nickelates. One finds a generic tendency
towards magnetic order accompanied by orbital polarization. For two equivalent
orbitals with diagonal hopping such orbitally polarized phases are induced by
finite crystal field.Comment: 2 pages, 2 figure
Soil organic phosphorus and microbial community composition as affected by 26years of different management strategies
Agricultural management can affect soil organic matter chemistry and microbial community structure, but the relationship between the two is not well understood. We investigated the effect of crop rotation, tillage and stubble management on forms of soil phosphorus (P) as determined by solution 31P nuclear magnetic resonance spectroscopy and microbial community composition using fatty acid methyl ester analysis in a long-term field experiment (26years) on a Chromic Luvisol in New South Wales, Australia. An increase in soil organic carbon, nitrogen and phosphorus compared to the beginning of the experiment was found in a rotation of wheat and subterranean clover with direct drill and mulching, while stubble burning in wheat-lupin and wheat-wheat rotations led to soil organic matter losses. Microbial biomass was highest in the treatment with maximum organic matter contents. The same soil P forms were detected in all samples, but in different amounts. Changes in organic P occurred mainly in the monoester region, with an increase or decrease in peaks that were present also in the sample taken before the beginning of the experiment in 1979. The microbial community composition differed between the five treatments and was affected primarily by crop rotations and to a lesser degree by tillage. A linkage between soil P forms and signature fatty acids was tentatively established, but needs to be verified in further studie
The Out-of-Equilibrium Time-Dependent Gutzwiller Approximation
We review the recently proposed extension of the Gutzwiller approximation, M.
Schiro' and M. Fabrizio, Phys. Rev. Lett. 105, 076401 (2010), designed to
describe the out-of-equilibrium time-evolution of a Gutzwiller-type variational
wave function for correlated electrons. The method, which is strictly
variational in the limit of infinite lattice-coordination, is quite general and
flexible, and it is applicable to generic non-equilibrium conditions, even far
beyond the linear response regime. As an application, we discuss the quench
dynamics of a single-band Hubbard model at half-filling, where the method
predicts a dynamical phase transition above a critical quench that resembles
the sharp crossover observed by time-dependent dynamical mean field theory. We
next show that one can actually define in some cases a multi-configurational
wave function combination of a whole set of mutually orthogonal Gutzwiller wave
functions. The Hamiltonian projected in that subspace can be exactly evaluated
and is equivalent to a model of auxiliary spins coupled to non-interacting
electrons, closely related to the slave-spin theories for correlated electron
models. The Gutzwiller approximation turns out to be nothing but the mean-field
approximation applied to that spin-fermion model, which displays, for any
number of bands and integer fillings, a spontaneous symmetry breaking
that can be identified as the Mott insulator-to-metal transition.Comment: 25 pages. Proceedings of the Hvar 2011 Workshop on 'New materials for
thermoelectric applications: theory and experiment
Residency time of agonists does not affect the stability of GPCR–arrestin complexes
Background and purpose: The interaction of arrestins with G-protein coupled receptors (GPCRs) desensitizes agonist-dependent receptor responses and often leads to receptor internalization. GPCRs that internalize without arrestin have been classified as "class A" GPCRs whereas "class B" GPCRs co-internalize with arrestin into endosomes. The interaction of arrestins with GPCRs requires both agonist activation and receptor phosphorylation. Here, we ask the question whether agonists with very slow off-rates can cause the formation of particularly stable receptor-arrestin complexes. Experimental approach: The stability of GPCR-arrestin-3 complexes at two class A GPCRs, the β2 -adrenoceptor and the μ opioid receptor, was assessed using two different techniques, fluorescence resonance energy transfer (FRET) and fluorescence recovery after photobleaching (FRAP) employing several ligands with very different off-rates. Arrestin trafficking was determined by confocal microscopy. Key results: Upon agonist washout, GPCR-arrestin-3 complexes showed markedly different dissociation rates in single-cell FRET experiments. In FRAP experiments, however, all full agonists led to the formation of receptor-arrestin complexes of identical stability whereas the complex between the μ receptor and arrestin-3 induced by the partial agonist morphine was less stable. Agonists with very slow off-rates could not mediate the co-internalization of arrestin-3 with class A GPCRs into endosomes. Conclusions and implications: Agonist off-rates do not affect the stability of GPCR-arrestin complexes but phosphorylation patterns do. Our results imply that orthosteric agonists are not able to pharmacologically convert class A into class B GPCRs
Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel
Ferromagnetic Nickel is the most celebrated iron group metal with pronounced
discrepancies between the experimental electronic properties and predictions of
density functional theories. In this work, we show in detail that the recently
developed multi-band Gutzwiller theory provides a very good description of the
quasi-particle band structure of nickel. We obtain the correct exchange
splittings and we reproduce the experimental Fermi-surface topology. The
correct (111)-direction of the magnetic easy axis and the right order of
magnitude of the magnetic anisotropy are found. Our theory also reproduces the
experimentally observed change of the Fermi-surface topology when the magnetic
moment is oriented along the (001)-axis. In addition to the numerical study, we
give an analytical derivation for a much larger class of variational
wave-functions than in previous investigations. In particular, we cover cases
of superconductivity in multi-band lattice systems.Comment: 35 pages, 3 figure
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