416 research outputs found
Structural distortions and orbital ordering in LaTiO3 and YTiO3
Theoretical investigations of the electronic, magnetic and structural
properties of LaTiO3 and YTiO3 have been made. In the framework of GGA and
GGA+U scheme we analyzed the effect of the local Coulomb interaction (U) value
on the atomic forces acting in the experimental structure. The optimal
parameters of the electron-electron on-site interactions as well as the orbital
configurations and magnetic properties are determined.Comment: 6 pages 6 figures, better quality pictures are avelable via e-mail,
Submitted to Europhysics Letter
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 correlations and competing orders in multiorbital dimers: a cluster DMFT study
We investigate the violation of the first Hund's rule in 4 and 5
transition metal oxides that form solids of dimers. Bonding states within these
dimers reduce the magnetization of such materials. We parametrize the dimer
formation with realistic hopping parameters and find not only regimes, where
the system behaves as a Fermi liquid or as a Peierls insulator, but also
strongly correlated regions due to Hund's coupling and its competition with the
dimer formation. The electronic structure is investigated using the cluster
dynamical mean-field theory for a dimer in the two-plane Bethe lattice with two
orbitals per site and -filling, that is three electrons per dimer. It
reveals dimer-antiferromagnetic order of a high-spin (double exchange) state
and a low-spin (molecular orbital) state. At the crossover region we observe
the suppression of long-range magnetic order, fluctuation enhancement and
renormalization of electron masses. At certain interaction strengths the system
becomes an incoherent antiferromagnetic metal with well defined local moments.Comment: 11 pages, 10 figure
Dynamical singlets and correlation-assisted Peierls transition in VO2
A theory of the metal-insulator transition in vanadium dioxide from the
high-temperature rutile to the low- temperature monoclinic phase is proposed on
the basis of cluster dynamical mean field theory, in conjunction with the
density functional scheme. The interplay of strong electronic Coulomb
interactions and structural distortions, in particular the dimerization of
vanadium atoms in the low temperature phase, plays a crucial role. We find that
VO2 is not a conventional Mott insulator, but that the formation of dynamical
V-V singlet pairs due to strong Coulomb correlations is necessary to trigger
the opening of a Peierls gap.Comment: 5 page
Targeting the Wnt pathways for therapies
The Wnt/β-catenin signaling pathway is crucial in animal development from sponges to humans. Its activity in the adulthood is less general, with exceptions having huge medical importance. Namely, improper activation of this pathway is carcinogenic in many tissues, most notably in the colon, liver and the breast. On the other hand, the Wnt/β-catenin signaling must be re-activated in cases of tissue damage, and insufficient activation results in regeneration failure and degeneration. These both medically important implications are unified by the emerging importance of this signaling pathway in the control of proliferation of various types of stem cells, crucial for tissue regeneration and, in case of cancer stem cells - cancer progression and relapse. This article aims at briefly reviewing the current state of knowledge in the field of Wnt signaling, followed by a detailed discussion of current medical developments targeting distinct branches of the Wnt pathway for anti-cancer and pro-regeneration therapies
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
Valence-band satellite in the ferromagnetic nickel: LDA+DMFT study with exact diagonalization
The valence-band spectrum of the ferromagnetic nickel is calculated using the
LDA+DMFT method. The auxiliary impurity model emerging in the course of the
calculations is discretized and solved with the exact diagonalization, or, more
precisely, with the Lanczos method. Particular emphasis is given to spin
dependence of the valence-band satellite that is observed around 6 eV below the
Fermi level. The calculated satellite is strongly spin polarized in accord with
experimental findings.Comment: REVTeX 4, 8 pages, 5 figure
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