  Fundamental quantities of QCD, such as the strong coupling and
$\Lambda_{QCD}$, are studied in the framework of lattice QCD with $N_f=2$
twisted mass fermions. In particular, the contact between lattice and
continuous calculations is made by comparing the renormalized ghost-gluon
vertex in MOM scheme with 4-loop perturbative results. A power correction is
needed in order to have agreement between the two descriptions. This suggests
the presence of a dimension-two $\VEV{A^2}$ gluon condensate whose value is
found to be higher than in the quanched case.
