10,778 research outputs found
Analytic continuation by averaging Pad\'e approximants
The ill-posed analytic continuation problem for Green's functions and
self-energies is investigated by revisiting the Pad\'{e} approximants
technique. We propose to remedy the well-known problems of the Pad\'{e}
approximants by performing an average of several continuations, obtained by
varying the number of fitted input points and Pad\'{e} coefficients
independently. The suggested approach is then applied to several test cases,
including Sm and Pr atomic self-energies, the Green's functions of the Hubbard
model for a Bethe lattice and of the Haldane model for a nano-ribbon, as well
as two special test functions. The sensitivity to numerical noise and the
dependence on the precision of the numerical libraries are analysed in detail.
The present approach is compared to a number of other techniques, i.e. the
non-negative least-square method, the non-negative Tikhonov method and the
maximum entropy method, and is shown to perform well for the chosen test cases.
This conclusion holds even when the noise on the input data is increased to
reach values typical for quantum Monte Carlo simulations. The ability of the
algorithm to resolve fine structures is finally illustrated for two relevant
test functions.Comment: 10 figure
Lattice dynamics of palladium in the presence of electronic correlations
We compute the phonon dispersion, density of states, and the Gr\"uneisen
parameters of bulk palladium in the combined density functional theory (DFT)
and dynamical mean-field theory (DMFT). We find good agreement with
experimental results for ground state properties (equilibrium lattice parameter
and bulk modulus) and the experimentally measured phonon spectra. We
demonstrate that at temperatures the phonon frequency in the
vicinity of the Kohn anomaly, , strongly decreases.
This is in contrast to DFT where this frequency remains essentially constant in
the whole temperature range. Apparently correlation effects reduce the
restoring force of the ionic displacements at low temperatures, leading to a
mode softening.Comment: minor revision
Electron correlations in MnGaAs as seen by resonant electron spectroscopy and dynamical mean field theory
After two decades from the discovery of ferromagnetism in Mn-doped GaAs, its
origin is still debated, and many doubts are related to the electronic
structure. Here we report an experimental and theoretical study of the valence
electron spectrum of Mn-doped GaAs. The experimental data are obtained through
the differences between off- and on-resonance photo-emission data. The
theoretical spectrum is calculated by means of a combination of
density-functional theory in the local density approximation and dynamical
mean-field theory (LDA+DMFT), using exact diagonalisation as impurity solver.
Theory is found to accurately reproduce measured data, and illustrates the
importance of correlation effects. Our results demonstrate that the Mn states
extend over a broad range of energy, including the top of the valence band, and
that no impurity band splits off from the valence band edge, while the induced
holes seem located primarily around the Mn impurity.Comment: 5 pages, 4 figure
Microscopic origin of Heisenberg and non-Heisenberg exchange interactions in ferromagnetic bcc Fe
By means of first principles calculations we investigate the nature of
exchange coupling in ferromagnetic bcc Fe on a microscopic level. Analyzing the
basic electronic structure reveals a drastic difference between the
orbitals of and symmetries. The latter ones define the shape of
the Fermi surface, while the former ones form weakly-interacting impurity
levels. We demonstrate that, as a result of this, in Fe the orbitals
participate in exchange interactions, which are only weakly dependent on the
configuration of the spin moments and thus can be classified as
Heisenberg-like. These couplings are shown to be driven by Fermi surface
nesting. In contrast, for the states the Heisenberg picture breaks down,
since the corresponding contribution to the exchange interactions is shown to
strongly depend on the reference state they are extracted from. Our analysis of
the nearest-neighbour coupling indicates that the interactions among
states are mainly proportional to the corresponding hopping integral and thus
can be attributed to be of double-exchange origin.Comment: 5 pages, 4 figure
Layer-resolved magnetic exchange interactions of surfaces of late 3d elements: effects of electronic correlations
We present the results of an ab initio study of magnetic properties of Fe, Co
and Ni surfaces. In particular, we discuss their electronic structure and
magnetic exchange interactions (Jij), as obtained by means of a combination of
density functional theory and dynamical mean-field theory. All studied systems
have a pronounced tendency to ferromagnetism both for bulk and surface atoms.
The presence of narrow-band surface states is shown to enhance the magnetic
moment as well as the exchange couplings. The most interesting results were
obtained for the Fe surface where the atoms have a tendency to couple
antiferromagnetically with each other. This interaction is relatively small,
when compared to interlayer ferromagnetic interaction, and strongly depends on
the lattice parameter. Local correlation effects are shown to lead to strong
changes of the overall shape of the spectral functions. However, they seem to
not play a decisive role on the overall picture of the magnetic couplings
studied here. We have also investigated the influence of correlations on the
spin and orbital moments of the bulk-like and surface atoms. We found that
dynamical correlations in general lead to enhanced values of the orbital
moment.Comment: 13 pages, 12 figure
Measurement invariance of the Satisfaction with Life Scale by sexual orientation
The Satisfaction with Life Scale (SWLS) has shown strong evidence of reliability, validity, and gender invariance, and there is some evidence of invariance across age, culture, and educational levels. So far, invariance across sexual orientation has not been studied, despite the number of works that relate well-being to sexual orientation. The SWLS should be invariant across sexual orientation to be able to compare group means. This study aimed to explore the invariance of the SWLS across sexual orientation. A non-probabilistic sample with 553 Spanish adults (208 males, 345 females; 212 heterosexuals, 182 gays, and 138 bisexuals among other sexual orientations) participated in a survey. We tested a one-factor model using confirmatory factor analysis. We tested the configural, metric, and scalar invariance of the factorial structure of the SWLS across sexual orientation with heterosexual, lesbian/gay, and bisexual groups. According to our results, the Spanish version of the SWLS shows scalar invariance across sexual orientations, allowing a valid comparison between sexual minority and heterosexual people. Moreover, in our sample, lesbian/gay and bisexual participants obtained lower scores in life satisfaction than heterosexual participants. Bisexual people obtained the lowest score in well-being compared with the other groups. Implications related to the importance of checking instrument invariance before comparing mean differences between groups are discussed.info:eu-repo/semantics/publishedVersio
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