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

TL;DR

This study uses computer simulations to analyze how size polydispersity affects the elastic properties of a degenerate f.c.c. crystal of soft dimers at zero temperature, revealing conditions for auxetic behavior.

Contribution

It introduces a detailed simulation analysis of polydisperse soft dimers, highlighting how polydispersity influences elastic constants and Poisson's ratio, including conditions for auxeticity.

Findings

Increasing polydispersity raises pressure and elastic constants.

Poisson's ratio is generally positive but can become negative with high polydispersity.

The system exhibits partial auxetic behavior at large polydispersity and n.

Abstract

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.