  We study an extended Hubbard model with on-site repulsion and nearest
neighbors attraction which tries to mimic some of the experimental features of
doped cuprates in the superconducting state. We draw and discuss the phase
diagram as a function of the effective interactions among electrons for a wide
range of doping concentrations. We locate the region which is relevant for the
cuprates setting some constraints on the parameters which may be used in this
kind of effective models. We also study the effects of temperature and
orthorrombicity on the symmetry and magnitude of the gap function, and map the
model onto a simpler linearized hamiltonian, which produces similar phase
diagrams.
