  The three gluon one particle irreducible function is investigated using
lattice QCD simulations over a large region of momentum in the Landau gauge for
four dimensional pure Yang-Mills equations and the SU(3) gauge group. The
results favor a zero crossing of the gluon form factor for momenta in the range
$220 - 260$ MeV. This zero crossing is required to happen in order to have a
properly defined set of Dyson-Schwinger equations. It is also shown that in the
high momentum region the lattice results are compatible with the predictions of
renormalisation group improved perturbation theory.
