Ferroelastic phase transition in two-dimensional molecular solids

Using constant-pressure molecular-dynamics simulation we have studied the nature of ferroelastic phase transition in two-dimensional molecular monolayers. For Lennard-Jones interaction parameters appropriate for ${\mathrm{O}}_2$ molecules, we find, in contrast to the prediction of the renormalization-group calculation of the associated Ginzburg-Landau-Wilson Hamiltonian, a first-order phase transition to the paraelastic phase precipitated by the formation of large density of localized defects of herringbonelike structure.