  We explore the possibility of improving the $\Lambda$CDM model at megaparsec
scales by introducing a scalar interaction which increases the mutual
gravitational attraction of dark matter particles. Using N-body simulations, we
study the spatial distribution of dark matter particles and halos. We measure
the effect of modifications in the Newton's gravity on properties of the
two-point correlation function, the dark matter power spectrum, the cumulative
halo mass function and density probability distribution functions. The results
look promising: the scalar interactions produce desirable features at
megaparsec scales without spoiling the $\Lambda$CDM successes at larger scales.
