3,848 research outputs found
Non-local Coulomb interactions and metal-insulator transition in TiO: a cluster LDA+DMFT approach
We present an ab initio quantum theory of the metal-insulator transition in
TiO. The recently developed cluster LDA+DMFT scheme is applied to
describe the many-body features of this compound. The conventional single site
DMFT cannot reproduce a low temperature insulating phase for any reasonable
values of the Coulomb interaction. We show that the non-local Coulomb
interactions and the strong chemical bonding within Ti-Ti pair is the origin of
the small gap insulating ground state of TiO
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
charge on Bk to exceed the atomic integer value by 0.22.Comment: 8 pages, 1 figur
Slave-rotor mean field theories of strongly correlated systems and the Mott transition in finite dimensions
The multiorbital Hubbard model is expressed in terms of quantum phase
variables (``slave rotors'') conjugate to the local charge, and of auxiliary
fermions, providing an economical representation of the Hilbert space of
strongly correlated systems. When the phase variables are treated in a local
mean-field manner, similar results to the dynamical mean-field theory are
obtained, namely a Brinkman-Rice transition at commensurate fillings together
with a ``preformed'' Mott gap in the single-particle density of states. The
slave- rotor formalism allows to go beyond the local description and take into
account spatial correlations, following an analogy to the superfluid-insulator
transition of bosonic systems. We find that the divergence of the effective
mass at the metal- insulator transition is suppressed by short range magnetic
correlations in finite-dimensional systems. Furthermore, the strict separation
of energy scales between the Fermi- liquid coherence scale and the Mott gap
found in the local picture, holds only approximately in finite dimensions, due
to the existence of low-energy collective modes related to zero-sound.Comment: 16 pages, 12 figure
Local magnetic moments in iron and nickel at ambient and Earth's core conditions
Some Bravais lattices have a particular geometry that can slow down the
motion of Bloch electrons by pre-localization due to the band-structure
properties. Another known source of electronic localization in solids is the
Coulomb repulsion in partially filled d- or f-orbitals, which leads to the
formation of local magnetic moments. The combination of these two effects is
usually considered of little relevance to strongly correlated materials. Here
we show that it represents, instead, the underlying physical mechanism in two
of the most important ferromagnets: nickel and iron. In nickel, the van Hove
singularity has an unexpected impact on the magnetism. As a result, the
electron-electron scattering rate is linear in temperature, in violation of the
conventional Landau theory of metals. This is true even at Earth's core
pressures, at which iron is instead a good Fermi liquid. The importance of
nickel in models of geomagnetism may have therefore to be reconsidered.Comment: Supplementary Information available at
https://www.nature.com/articles/ncomms16062#supplementary-informatio
Double Counting in LDA+DMFT - The Example of NiO
An intrinsic issue of the LDA+DMFT approach is the so called double counting
of interaction terms. How to choose the double-counting potential in a manner
that is both physically sound and consistent is unknown. We have conducted an
extensive study of the charge transfer system NiO in the LDA+DMFT framework
using quantum Monte Carlo and exact diagonalization as impurity solvers. By
explicitly treating the double-counting correction as an adjustable parameter
we systematically investigated the effects of different choices for the double
counting on the spectral function. Different methods for fixing the double
counting can drive the result from Mott insulating to almost metallic. We
propose a reasonable scheme for the determination of double-counting
corrections for insulating systems.Comment: 7 pages, 6 figure
Electronic Structure and Magnetic Properties of Solids
We review basic computational techniques for simulations of various magnetic
properties of solids. Several applications to compute magnetic anisotropy
energy, spin wave spectra, magnetic susceptibilities and temperature dependent
magnetisations for a number of real systems are presented for illustrative
purposes.Comment: Review article; To appear in Journal of Computational Crystallograph
An dynamical-mean-field-theory investigation of specific heat and electronic structure of and -plutonium
We have carried out a comparative study of the electronic specific heat and
electronic structure of and -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, , 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 . In the second, , plutonium is viewed as being close
to an configuration, and perturbation theory is carried out around the
(LDA+U) starting point bit below . In the latter case the electronic
specific heat coefficient attains a smaller value in -Pu than
in -Pu, in contradiction to experiment, while in the former case our
calculations reproduce the experimentally observed large increase of
in -Pu as compared to the phase. This enhancement of the
electronic specific heat coefficient in -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 . The densities
of states of and -plutonium obtained starting from the
open-shell configuration are also in good agreement with the experimental
photoemission spectra.Comment: 6 pages, 3 figure
Non-perturbative model and ferromagnetism in dilute magnets
We calculate magnetic couplings in the model for dilute magnets, in
order both to identify the relevant parameters which control ferromagnetism and
also to bridge the gap between first principle calculations and model
approaches. The magnetic exchange interactions are calculated
non-perturbatively and disorder in the configuration of impurities is treated
exacly, allowing us to test the validity of effective medium theories.
Results differ qualitatively from those of weak coupling. In contrast to mean
field theory, increasing may not favor high Curie temperatures:
scales primarily with the bandwidth. High temperature ferromagnetism at small
dilutions is associated with resonant structure in the p-band. Comparison to
diluted magnetic semiconductors indicate that Ga(Mn)As has such a resonant
structure and thus this material is already close to optimality.Comment: 4 pages, 4 Figure
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