Dark energy and the mass of galaxy clusters

Up to now, dark energy evidences are based on the dynamics of the universe on very large scales, above 1 Gpc. Assuming it continues to behave like a cosmological constant $\Lambda$ on much smaller scales, I discuss its effects on the motion of nonrelativistic test particles in a weak gravitational field, and I propose a way to detect evidences of $\Lambda \ne 0$ at the scale of about 1 Mpc: the main ingredient is the measurement of galaxy cluster masses.