  It is presented a numerical study on the unjamming packing fraction of bi-
and polydisperse disk packings, which are generated through compression of a
monodisperse crystal. In bidisperse systems, a fraction f_+ = 40% up to 80% of
the total number of particles have their radii increased by \Delta R, while the
rest has their radii decreased by the same amount. Polydisperse packings are
prepared by changing all particle radii according to a uniform distribution in
the range [-\Delta R,\Delta R]. The results indicate that the critical packing
fraction is never larger than the value for the initial monodisperse crystal,
\phi = \pi/12, and that the lowest value achieved is approximately the one for
random close packing. These results are seen as a consequence of the interplay
between the increase in small-small particle contacts and the local crystalline
order provided by the large-large particle contacts.
