  A simple semiclassical H\'enon-Heiles model is constructed based on Dirac's
time-dependent variational principle. We obtain an effective semiclassical
Hamiltonian using a Hatree-type two-body trial wavefunction in the
Jackiw-Kerman form. Numerical results show that quantum effects can in fact
induce chaos in the non-chaotic regions of the classical H\'enon-Heiles model.
