  We show that for nanoparticles with giant polarizability $\alpha$ (a
prominent example being the recently studied Na$_{14}$F$_{13}$ molecular
clusters) van der Waals forces are significantly enhanced at interparticle
distances shorter than $R_0=(\alpha/2\pi\epsilon_0)^{1/3}$. For an adequate
description of this phenomenon, nonlinear effects must be taken into account.
We show that, contrary to some theoretical claims, an accurate treatment of
nonlinearity does not lead to any repulsive forces.
