39 research outputs found
MODEL DECISION MAKING BY INTELLECTUAL SYSTEM ON BASE OF THE ILLDEFINED PROCEDURAL SEMANTIC NETWORK
In article is offered procedural model of the presentation of the knowledges, providing planning the goal-directed behavior of the intellectual systems in process of instrumental activity
THEORETICAL BASE TO ORGANIZATIONS OF THE CONCLUSION OF THE CONCLUSIONS IN NONMONOTONIC AMBIENCE ON BASE CONDITIONALLYHUNG VARIABLE
It is offered one of the approach to organizations of the notional thinking of the intellectual systems, connected with development theoretical base conclusion of the conclusions in free non monotonic problem-solving area on base conditionally hung variable
Surface states and their possible role in the superconductivity of MgB2
We report layer-Korringa-Kohn-Rostocker calculations for bulk and surface
states as well as the corresponding angle resolved photoemission (ARPES)
intensities of MgB2. Our theoretical results reproduce very well the recent
ARPES data by Uchiyama et al., cond-mat/0111152. At least two surface states
are assigned. Consequences of SFS on the anisotropy of the upper critical
fields and other properties in the superconducting state of small grains in
micropowder samples are briefly discussed.Comment: 4pages, 6figures, corrected typos, references adde
Appearance of Half-Metallicity in the Quaternary Heusler Alloys
I report systematic first-principle calculations of the quaternary Heusler
alloys like Co[CrMn]Al, CoMn[AlSn] and
[FeCo]MnAl. I show that when the two limiting cases (x=0 or 1)
correspond to a half-metallic compound, so do the intermediate cases. Moreover
the total spin moment in scales linearly with the total number of
valence electrons (and thus with the concentration ) following the
relation , independently of the origin of the extra valence
electrons, confirming the Slater-Pauling behavior of the normal Heusler alloys.
Finally I discuss in all cases the trends in the atomic projected DOSs and in
the atomic spin moments.Comment: 4 pages, 3 figures, 2 Table
Electronic Structure of Sr_2FeMoO_6
We have analysed the unusual electronic structure of Sr_2FeMoO_6 combining
ab-initio and model Hamiltonian approaches. Our results indicate that there are
strong enhancements of the intraatomic exchange strength at the Mo site as well
as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss
the possibility of a negative effective Coulomb correlation strength (U_{eff})
at the Mo site due to these renormalised interaction strengths.Comment: To appear in Phys. Rev. Let
Spin-orbit splitting of image states
We quantify the effect of the spin-orbit interaction on the Rydberg-like
series of image state electrons at the (111) and (001) surface of Ir, Pt and
Au. Using relativistic multiple-scattering methods we find Rashba-like
dispersions with Delta E(K)=gamma K with values of gamma for n=1 states in the
range 38-88 meV Angstrom. Extending the phase-accumulation model to include
spin-orbit scattering we find that the splittings vary like 1/(n+a)^3 where a
is the quantum defect and that they are related to the probability of spin-flip
scattering at the surface. The splittings should be observable experimentally
being larger in magnitude than some exchange-splittings that have been resolved
by inverse photoemission, and are comparable to linewidths from inelastic
lifetimes.Comment: 10 pages, 4 figure
Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni
We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra-atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean-field theory in the static limit is
emphasized. Both experimental magnitude of MAE and direction of magnetization
are predicted correctly near U=4 eV for Ni and U=3.5 eV for Fe. Correlations
modify one-electron spectra which are now in better agreement with experiments.Comment: 4 pages, 2 figure
First- principle calculations of magnetic interactions in correlated systems
We present a novel approach to calculate the effective exchange interaction
parameters based on the realistic electronic structure of correlated magnetic
crystals in local approach with the frequency dependent self energy. The analog
of ``local force theorem'' in the density functional theory is proven for
highly correlated systems. The expressions for effective exchange parameters,
Dzialoshinskii- Moriya interaction, and magnetic anisotropy are derived. The
first-principle calculations of magnetic excitation spectrum for ferromagnetic
iron, with the local correlation effects from the numerically exact QMC-scheme
is presented.Comment: 17 pages, 3 Postscript figure
An embedding scheme for the Dirac equation
An embedding scheme is developed for the Dirac Hamiltonian H. Dividing space
into regions I and II separated by surface S, an expression is derived for the
expectation value of H which makes explicit reference to a trial function
defined in I alone, with all details of region II replaced by an effective
potential acting on S and which is related to the Green function of region II.
Stationary solutions provide approximations to the eigenstates of H within I.
The Green function for the embedded Hamiltonian is equal to the Green function
for the entire system in region I. Application of the method is illustrated for
the problem of a hydrogen atom in a spherical cavity and an Au(001)/Ag/Au(001)
sandwich structure using basis sets that satisfy kinetic balance.Comment: 16 pages, 5 figure
One-dimensional dynamics of the d-electrons in -NaVO
We have studied the electronic properties of the ladder compound
-NaVO, adopting a joint experimental and theoretical
approach. The momentum-dependent loss function was measured using electron
energy-loss spectroscopy in transmission. The optical conductivity derived from
the loss function by a Kramers-Kronig analysis agrees well with our results
from LSDA+U band-structure calculations upon application of an
antiferromagnetic alignment of the V~3 spins along the legs and an
on-site Coulomb interaction U of between 2 and 3 eV. The decomposition of the
calculated optical conductivity into contributions from transitions between
selected energy regions of the DOS reveals the origin of the observed
anisotropy of the optical conductivity. In addition, we have investigated the
plasmon excitations related to transitions between the vanadium states within
an effective 16 site vanadium cluster model. Good agreement between the
theoretical and experimental loss function was obtained using the hopping
parameters derived from the tight binding fit to the band-structure and
moderate Coulomb interactions between the electrons within the ab plane.Comment: 23 pages, 8 figures; submitted to PR