ELECTRONIC-STRUCTURE OF THE CUO3 CHAINS IN RBA(2)CU(3)O(6+X) (R=Y OR A RARE-EARTH)

We consider the appropriate generalization of the three-band Hubbard model to describe the CuO3 chains of RBa(2)Cu(3)O(6+x) (R = Y or a rare earth). The model is mapped numerically into a t-J model with t similar to 0.85 eV and J similar to 0.2 eV. Making the reasonable assumption that similar to 5% of the O atoms between two Cu atoms are lacking, the model allows an explanation of the optical conductivity sigma(omega) of the chains, the small change of the occupation of the chains when Y is substituted by Pr, and the charge corrugations observed by scanning-tunneling microscopy.