Redes de ions de valencia intermediaria

AUTOR(ES)
DATA DE PUBLICAÇÃO

1989

RESUMO

In this work we address the problem of a lattice of Intermediate Valence ions by using a perturbation method especially designed for these systems. We describe the model with atomic transfer operators between fn and fn+1 states of the internal 4f shells of these materiais. The hybridization interaction with the band it taken as the perturbation. In order to obtain the diagrams of the perturbative series we have used the cumulant transformation and a generalization or Wick s theorem for these ionic operators. The Green s function for the f-electrons is calculated within this scheme. Two interesting cases or the model are analyzed: the Anderson lattice (J1 = O, J2 = 1/2) which simulates Cerium compounds, and a case with two magnetic configurations (J1 = 1/2, J2 = 1) which in turn simulates Thulium compounds. The coherent scattering approximation, so-called chain approximation; opens a gap in the density of states near the local energy level which is proportional to the hybridization parameter reduced by a scaling factor Dm <1. This approximation, the gap and the curve form, recalls the mean field solution of the "slave boson" method. Further corrections to the chain approximation including two-particle correlations keep the gap structure for the LDOS. However, new states appear filling in the gap for the Intermediate Valence region. The results are analyzed in the limiting cases of zero bandwidth, where the exact solution is available to compare with, and for the cage of finite bandwidth whose analysis can be done numerically. We can conclude from these results that the method, here developed, has good possibilities of application to real systems

ASSUNTO(S)

ions valencia (quimica teorica)

ACESSO AO ARTIGO

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