  We evaluate the one-particle and double-occupied Green functions for the
Hubbard model at half-filling using the moment approach of Nolting. Our
starting point is a self-energy, $\Sigma(\vec{k},\omega)$, which has a single
pole, $\Omega(\vec{k})$, with {\it spectral} weight, $\alpha(\vec{k})$, and
quasi-particle lifetime, $\gamma(\vec{k})$. In our approach,
$\Sigma(\vec{k},\omega)$ becomes the central feature of the many-body problem
and due to three unkown $\vec{k}$-parameters we have to satisfy only the first
three sum rules instead of four as in the canonical formulation of Nolting.
This self-energy choice forces our system to be a non-Fermi liquid for any
value of the interaction, since it does not vanish at zero frequency. The
one-particle Green function, $G(\vec{k},\omega)$, shows the finger-print of a
strongly correlated system, i.e., a double peak structure in the one-particle
spectral density, $A(\vec{k},\omega)$, vs $\omega$ for intermediate values of
the interaction. Close to the Mott Insulator-Transition, $A(\vec{k},\omega)$,
becomes a wide single peak, signaling the absence of quasi-particles.
