259 research outputs found
Nature of the Mott transition in Ca2RuO4
We study the origin of the temperature-induced Mott transition in Ca2RuO4. As
a method we use the local-density approximation+dynamical mean-field theory. We
show the following. (i) The Mott transition is driven by the change in
structure from long to short c-axis layered perovskite (L-Pbca to S-Pbca); it
occurs together with orbital order, which follows, rather than produces, the
structural transition. (ii) In the metallic L-Pbca phase the orbital
polarization is ~0. (iii) In the insulating S-Pbca phase the lower energy
orbital, ~xy, is full. (iv) The spin-flip and pair-hopping Coulomb terms reduce
the effective masses in the metallic phase. Our results indicate that a similar
scenario applies to Ca_{2-x}Sr_xRuO_4 (x<0.2). In the metallic x< 0.5
structures electrons are progressively transferred to the xz/yz bands with
increasing x, however we find no orbital-selective Mott transition down to ~300
K.Comment: 4 pages, 3 figures; published versio
Many-body effects on Cr(001) surfaces: An LDA+DMFT study
The electronic structure of the Cr(001) surface with its sharp resonance at
the Fermi level is a subject of controversial debate of many experimental and
theoretical works. To date, it is unclear whether the origin of this resonance
is an orbital Kondo or an electron-phonon coupling effect. We have combined ab
initio density functional calculations with dynamical mean-field simulations to
calculate the orbitally resolved spectral function of the Cr(001) surface. The
calculated orbital character and shape of the spectrum is in agreement with
data from (inverse) photoemission experiments. We find that dynamic electron
correlations crucially influence the surface electronic structure and lead to a
low energy resonance in the and orbitals. Our results
help to reconvene controversial experimental results from (I)PES and STM
measurements.Comment: 8 pages, 5 figure
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
Orbital Kondo effect in Cobalt-Benzene sandwich molecules
We study a Co-benzene sandwich molecule bridging the tips of a Cu nanocontact
as a realistic model of correlated molecular transport. To this end we employ a
recently developed method for calculating the correlated electronic structure
and transport properties of nanoscopic conductors. When the molecule is
slightly compressed by the tips of the nanocontact the dynamic correlations
originating from the strongly interacting Co 3d shell give rise to an orbital
Kondo effect while the usual spin Kondo effect is suppressed due to Hund's rule
coupling. This non-trivial Kondo effect produces a sharp and
temperature-dependent Abrikosov-Suhl resonance in the spectral function at the
Fermi level and a corresponding Fano line shape in the low bias conductance
A Self-consistent DFT+DMFT scheme in the Projector Augmented Wave : Applications to Cerium, Ce2O3 and Pu2O3 with the Hubbard I solver and comparison to DFT+U
An implementation of full self-consistency over the electronic density in the
DFT+DMFT framework on the basis of a plane wave-projector augmented wave (PAW)
DFT code is presented. It allows for an accurate calculation of the total
energy in DFT+DMFT within a plane wave approach. In contrast to frameworks
based on the maximally localized Wannier function, the method is easily applied
to f electron systems, such as cerium, cerium oxide (Ce2O3) and plutonium oxide
(Pu2O3). In order to have a correct and physical calculation of the energy
terms, we find that the calculation of the self-consistent density is
mandatory. The formalism is general and does not depend on the method used to
solve the impurity model. Calculations are carried out within the Hubbard I
approximation, which is fast to solve, and gives a good description of strongly
correlated insulators. We compare the DFT+DMFT and DFT+U solutions, and
underline the qualitative differences of their converged densities. We
emphasize that in contrast to DFT+U, DFT+DMFT does not break the spin and
orbital symmetry. As a consequence, DFT+DMFT implies, on top of a better
physical description of correlated metals and insulators, a reduced occurrence
of unphysical metastable solutions in correlated insulators in comparison to
DFT+U.Comment: 19 pages, 9 figures. This is an author-created, un-copyedited version
of an article accepted for publication in Journal of Physics: Condensed
Matter. IOP Publishing Ltd is not responsible for any errors or omissions in
this version of the manuscript or any version derived from it. The Version of
Record is available online at doi: 10.1088/0953-8984/24/7/07560
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