6,978 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
Deconfinement transition and Luttinger to Fermi Liquid crossover in quasi one-dimensional systems
We investigate a system of one dimensional Hubbard chains of interacting
fermions coupled by inter-chain hopping. Using a generalization of the
Dynamical Mean Field Theory we study the deconfinement transition from a Mott
insulator to a metal and the crossover between Luttinger and Fermi liquid
phases. One-particle properties, local spin response and inter-chain optical
conductivity are calculated. Possible applications to organic conductors are
discussed.Comment: 5 page
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
Organizational Control Systems and Software Quality: A Cross-National Study.
This study explores the relationship between organizational control modes (behavior, outcome, and clan) andsoftware quality. Much of the previous work on organizational control has examined the choice of modes giventask characteristics. This research extends work in control theory by considering the impact of control modeson the increasingly critical organizational outcome of software quality. The research is set in the context ofsoftware development organizations in three of the largest software developing countries: India, Ireland, andIsrael (the 3Is). A cross sectional survey of 400 software development organizations across the 3Is will be usedto test the developed model. In addition to the theoretical contributions, the study will provide practicalimplications to support software project managers in making better organizational control choices
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
Strong Coupling Solver for the Quantum Impurity Model
We propose a fast impurity solver for the general quantum impurity model
based on the perturbation theory around the atomic limit, which can be used in
combination with the local density approximation (LDA) and the dynamical mean
field theory (DMFT). We benchmark the solver in the two band Hubbard model
within DMFT against quantum Monte Carlo (QMC) and numerical renormalization
group (NRG) results. We find that the solver works very well in the
paramagnetic Mott insulator phase. We also apply this impurity solver to the
DMFT study of the anti-ferromagnetic phase transition in the unfrustrated Bethe
lattice. The Neel temperature obtained by the fast impurity solver agrees very
well with the QMC results in the large Hubbard U limit. The method is a
promising tool to be used in combination with the LDA+DMFT to study Mott
insulators starting from first principles.Comment: 5 pages, 5 figures. to be published in Physical Review
Excitonic Instability and Pseudogap Formation in Nodal Line Semimetal ZrSiS
Electron correlation effects are studied in ZrSiS using a combination of
first-principles and model approaches. We show that basic electronic properties
of ZrSiS can be described within a two-dimensional lattice model of two nested
square lattices. High degree of electron-hole symmetry characteristic for ZrSiS
is one of the key features of this model. Having determined model parameters
from first-principles calculations, we then explicitly take electron-electron
interactions into account and show that at moderately low temperatures ZrSiS
exhibits excitonic instability, leading to the formation of a pseudogap in the
electronic spectrum. The results can be understood in terms of
Coulomb-interaction-assisted pairing of electrons and holes reminiscent to that
of an excitonic insulator. Our finding allows us to provide a physical
interpretation to the unusual mass enhancement of charge carriers in ZrSiS
recently observed experimentally.Comment: 6 pages, 4 figures. Final versio
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