Poisson's ratio of orientationally disordered hard dumbbell crystal in three dimensions

Elastic properties of a rotator phase of hard homonuclear dumbbells are determined by constant pressure Monte Carlo simulations. Simple approximations expressing the influence of molecular anisotropy on the elastic constants and Poisson's ratio are found. The maximum density at which the dumbbells with their mass centers fixed at the lattice sites can freely rotate is observed to be strongly correlated with the density at which C12 = C44. It is also shown that Poisson's ratio measured along any direction and averaged with respect to directions transverse to it is always positive. At any fixed pressure, the averaged Poisson ratio increases with increasing dumbbell anisotropy.