  The evolution of galaxy clusters can be affected by the repulsion described
by the cosmological constant. This conclusion is reached within the modified
weak-field General Relativity approach where the cosmological constant \Lambda
enables to describe the common nature of the dark matter and the dark energy.
Geometrical methods of theory of dynamical systems and the Ricci curvature
criterion are used to reveal the difference in the instability properties of
galaxy clusters which determine their evolutionary paths. Namely, it is shown
that the clusters determined by the gravity with \Lambda-repulsion tend to
become even more unstable than those powered only by Newtonian gravity, the
effect to be felt at cosmological time scales.
