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

We consider the appropriate generalization of the three-band Hubbard m odel 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 simil ar to 0.85 eV and J similar to 0.2 eV. Making the reasonable assumptio n that similar to 5% of the O atoms between two Cu atoms are lacking, the model allows an explanation of the optical conductivity sigma(omeg a) of the chains, the small change of the occupation of the chains whe n Y is substituted by Pr, and the charge corrugations observed by scan ning-tunneling microscopy.