Negative Poisson’s ratio of two-dimensional hard cyclic tetramers

A two-dimensional system of hard, cyclic tetramers has been investigated by constant pressure Monte Carlo (MC) simulations with variable shape of the periodic box. The molecules (tetramers) are composed of four identical hard disks (atoms) with centers forming a square with sides equal to the diameter of the disks. The elastic constants and the Poisson’s ratio are determined by the analysis of strain fluctuations and the reference state of the system. The singular behavior of the elastic constants is in agreement with free volume theory. It has been found that the hard cyclic tetramer system is auxetic – that is, the Poisson’s ratio of the tetramer system is negative.