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تسجيل مستخدم جديدElectronic structure of the $rm Ca_3Co_4O_9$ compound from ab initio local interactions
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Julien Soret
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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 $a_{1g}$ orbitals of the cobalt atoms ; the $e_g$ being always lower in energy by more than 240,meV. The electron correlation is found very large $U/tsim 26$ as well as the parameters fluctuations as a function of the structural modulation. The main consequences are a partial $a_{1g}$ electrons localization and a fluctuation of the in-plane magnetic exchange from AFM to FM. The behavior of the Seebeck coefficient as a function of temperature is discussed in view of the ab initio results, as well as the 496,K phase transition.
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