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We used quantum chemical ab initio methods to determine the effective parameters of Hubbard and $t-J$ models for the $rm Na_{x}CoO_2$ compounds (x=0 and 0.5). As for the superconducting compound we found the $a_{1g}$ cobalt orbitals above the $e_g^prime$ ones by a few hundreds of meV due to the $e_g^prime$--$e_g$ hybridization of the cobalt $3d$ orbitals. The correlation strength was found to increase with the sodium content $x$ while the in-plane AFM coupling decreases. The less correlated system was found to be the pure $CoO_2$, however it is still strongly correlated and very close to the Mott transition. Indeed we found $U/tsim 15$, which is the critical value for the Mott transition in a triangular lattice. Finally, one finds the magnetic exchanges in the $rm CoO_2$ layers, strongly dependant of the weak local structural distortions.
We used fully correlated ab initio calculations to determine the effective parameters of Hubbard and t - J models for the thermoelectric misfit compound $rm Ca_3Co_4O_9$. As for the $rm Na_xCoO_2$ family the Fermi level orbitals are the $a_{1g}$ orbi
The present paper proposes the direct calculation of the microscopic contributions to the magneto-electric coupling, using ab initio methods. The electrostrictive and the Dzyaloshinskii-Moriya contributions were evaluated individually. For this purpo
RESPACK is a first-principles calculation software for evaluating the interaction parameters of materials and is able to calculate maximally localized Wannier functions, response functions based on the random phase approximation and related optical p
We propose a new ab initio method designed for the accurate calculation of effective exchange integrals between atoms with numerous open-shells. This method applies to ferromagnetic as well as antiferromagnetic exchange, direct or ligand-mediated exc
The anomalous plasmon linewidth dispersion (PLD) measured in K by vom Felde, Sprosser-Prou, and Fink (Phys. Rev. B 40, 10181 (1989)), has been attributed to strong dynamical electron-electron correlations. On the basis of ab initio response calculati