  We study a 3-band extended Hubbard model on a CuO_3 system by the density
matrix renormalization group (DMRG) method. Our system has geometry similar to
that of a section of the CuO_2 plane of the copper-oxide superconductors. We
have studied the effects of nearest-neighbour repulsions on the current-current
correlations of two model CuO_3 systems. We show that repulsive interactions
are clearly capable of increasing the magnitude of the current-current
correlations in both models studied. The long-distance behavior of the
current-current correlations is qualitatively influenced by V. We show that
repulsive interactions are capable of enhancing correlations involving at least
one copper-oxygen rung over distances comparable to the length of the system.
In some cases, V decreases the exponent corresponding to the power-law decay,
leading to a considerable slowing down of the long-distance decay of the
current-current correlations, compared to that of the Hubbard model.

Strongly Correlated Electrons;Superconductivity