  Using the trace anomaly and low energy relations, as well as the
Witten-Veneziano formula for the mass of the $\eta'$ meson, we have developed a
formalism which makes it possible to express the gluon condensate, the
topological susceptibility and the mass of the $\eta'$ meson as a functions of
the truly nonperturbative vacuum energy density which is one of the most
important characteristics of the QCD true ground state. It was directly applied
to the numerical evaluation of the chiral QCD vacuum topological structure
within its quantum zero momentum modes enhancement model. A rather good
agreement with phenomenological and experimental values of the above-mentioned
quantities has been achieved. With the help of the Witten-Veneziano formula, we
derived an absolute lower bounds for the pion decay constant and the mass of
the $\eta'$ meson in the chiral limit. By introducing the most general
parametrization of the gluon condensate, we also proposed how the correct $N_f$
(number of flavors) dependence of its phenomenologically extracted value could
be restored.
