Elastic properties of degenerate f.c.c. crystal of polydisperse soft dimers at zero temperature

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 1/2; 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 in pressure, elastic constants and Poisson's ratio; the latter is positive in most directions. A direction is found, however, in which the size polydispersity causes a substantial decrease in Poisson's ratio, down to negative values for large n. Thus, the system is partially auxetic for large polydispersity and large n.