  Using the effective potential approach for composite operators, we have
formulated a general method of calculation of the truly non-perturbative
Yang-Mills vacuum energy density (this is, by definition, the Bag constant
apart from the sign). It is the main dynamical characteristic of the QCD ground
state. Our method allows one to make it free of the perturbative contributions
('contaminations'), by construction. We also perform an actual numerical
calculation of the Bag constant for the confining effective charge. Its choice
uniquely defines the Bag constant, which becomes free of all the types of the
perturbative contributions now, as well as possessing many other desirable
properties as colorless, gauge independence, etc. Using further the trace
anomaly relation, we develop a general formalism which makes it possible to
relate the Bag constant to the gluon condensate not using the weak coupling
solution for the corresponding $\beta$ function. Our numerical result for the
Bag constant shows a good agreement with other phenomenological estimates of
the gluon condensate.
