Elastic properties of the 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 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.