  Elastic properties of soft, three-dimensional dimers, interacting through
site-site n-inverse-power potential, are determined by computer simulations at
zero temperature. The degenerate crystal of dimers exhibiting (Gaussian) size
distribution of atomic diameters - i.e. size polydispersity - is studied at the
molecular number density $1/\sqrt{2}$; the distance between centers of atoms
forming dimers is considered as a length unit. It is shown that, at the fixed
number density of the dimers, increasing polydispersity causes, typically, an
increase of pressure, elastic constants and Poisson's ratio; the latter is
positive in most direction. A direction is found, however, in which the size
polydispersity causes substantial decrease of Poisson's ratio, down to negative
values for large $n$. Thus, the system is partially auxetic for large
polydispersity and large n.
