  We determine the quantum phase diagram of the one-dimensional Hubbard model
with bond-charge interaction X in addition to the usual Coulomb repulsion U at
half-filling. For large enough X and positive U the model shows three phases.
For large U the system is in the spin-density wave phase already known in the
usual Hubbard model. As U decreases, there is first a spin transition to a
spontaneously dimerized bond-ordered wave phase and then a charge transition to
a novel phase in which the dominant correlations at large distances correspond
to an incommensurate singlet superconductor.
