1,481 research outputs found
Role of electronic correlations in the Fermi surface formation of NaCoO
Band structure of metallic sodium cobaltate NaCoO (=0.33, 0.48,
0.61 0.72) has been investigated by local density approximation+Hubbard
(LDA+) method and within Gutzwiller approximation for the Co-
manifold. Correlation effects being taken into account results in suppression
of the hole pockets at the Fermi surface in agreement with recent
angle-resolved photo-emission spectroscopy (ARPES) experiments. In the
Gutzwiller approximation the bilayer splitting is significantly reduced due to
the correlation effects. The formation of high spin (HS) state in Co -shell
was shown to be very improbable.Comment: 6 pages, 2 figure
The influence of the rare earth ions radii on the Low Spin to Intermediate Spin state transition in lanthanide cobaltite perovskites: LaCoO3 vs. HoCoO3
We present first principles LDA+U calculations of electronic structure and
magnetic state for LaCoO3 and HoCoO3. Low Spin to Intermediate Spin state
transition was found in our calculations using experimental crystallographic
data for both materials with a much higher transition temperature for HoCoO3,
which agrees well with the experimental estimations. Low Spin state t6e0
(non-magnetic) to Intermediate Spin state t5e1 (magnetic) transition of Co(3+)
ions happens due to the competition between crystal field t_2g-e_g splitting
and effective exchange interaction between 3 spin-orbitals. We show that the
difference in crystal structure parameters for HoCoO3 and LaCoO3 due to the
smaller ionic radius of Ho ion comparing with La ion results in stronger
crystal field splitting for HoCoO3 (0.09 eV ~ 1000 K larger than for LaCoO3)
and hence tip the balance between the Low Spin and Intermediate Spin states to
the non-magnetic solution in HoCoO3.Comment: 13 pages, 6 figure
Technological schemes of the formation internal dumps and determination the parameters of excavator`s dumps by working off the deep open pits
Проаналізовані основні схеми внутрішнього відвалоутворення при відпрацюванні глибоких кар’єрів і запропонована класифікація цих схем. Отримана аналітична залежність площі
призми зсуву гірської маси від параметрів обладнання і фізико-механічних властивостей
скельних порід.
Проанализированы основные схемы внутреннего отвалообразования при отработке глубоких карьеров и предложена классификация этих схем. Получена аналитическая зависимость площади призмы сдвижения горной массы от параметров оборудования и физико-механических свойств скальных пород
First-principles Calculations of the Electronic Structure and Spectra of Strongly Correlated Systems: Dynamical Mean-field Theory
A recently developed dynamical mean-field theory in the iterated perturbation
theory approximation was used as a basis for construction of the "first
principles" calculation scheme for investigating electronic structure of
strongly correlated electron systems. This scheme is based on Local Density
Approximation (LDA) in the framework of the Linearized Muffin-Tin-Orbitals
(LMTO) method. The classical example of the doped Mott-insulator
La_{1-x}Sr_xTiO_3 was studied by the new method and the results showed
qualitative improvement in agreement with experimental photoemission spectra.Comment: 11 pages, 3 Postscript figures, LaTeX, submit in Journal of Physics:
Condensed Matte
Pressure-driven metal-insulator transition in BiFeO from Dynamical Mean-Field Theory
A metal-insulator transition (MIT) in BiFeO under pressure was
investigated by a method combining Generalized Gradient Corrected Local Density
Approximation with Dynamical Mean-Field Theory (GGA+DMFT). Our paramagnetic
calculations are found to be in agreement with experimental phase diagram:
Magnetic and spectral properties of BiFeO3 at ambient and high pressures were
calculated for three experimental crystal structures , and
. At ambient pressure in the phase, an insulating gap of 1.2
eV was obtained in good agreement with its experimental value. Both and
phases have a metal-insulator transition that occurs simultaneously with
a high-spin (HS) to low-spin (LS) transition. The critical pressure for the
phase is 25-33 GPa that agrees well with the experimental observations.
The high pressure and temperature phase exhibits a metallic
behavior observed experimentally as well as in our calculations in the whole
range of considered pressures and undergoes to the LS state at 33 GPa where a
to transition is experimentally observed. The
antiferromagnetic GGA+DMFT calculations carried out for the structure
result in simultaneous MIT and HS-LS transitions at a critical pressure of 43
GPa in agreement with the experimental data
The role of temperature and Coulomb correlation in stabilization of CsCl-phase in FeS under pressure
The iron-sulfur system is important for planetary interiors and is intensely
studied, particularly for better understanding of the cores of Mars and Earth.
Yet, there is a paradox about high-pressure stability of FeS: ab initio global
optimization (at DFT level) predicts a Pmmn phase (with a distorted rocksalt
structure) to be stable at pressures above ~120 GPa, which has not yet been
observed in the experiments that instead revealed a CsCl-type phase which,
according to density functional calculations, should not be stable. Using
quasiharmonic free energy calculations and the dynamical mean field theory, we
show that this apparent discrepancy is removed by proper account of electron
correlations and entropic effects.Comment: 5 pages, 3 figure
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