Nonperiodic solid phase in a two-dimensional hard-dimer system

Abstract

We report Monte Carlo simulations of a system of two-dimensional, hard, homonuclear dimers. The equation of state and the Gibbs free energy were computed for the fluid phase and several crystalline and noncrystalline (aperiodic) solid structures. We observe that the differences in Gibbs free energy between the various solid structures are much less than the contribution to the entropy due to degeneracy of the ‘‘ground state’’ of the aperiodic solid. Hence, the thermodynamically stable solid structure of the system corresponds to an aperiodic arrangement of the molecular centers of mass and orientations. The melting point determined for this aperiodic solid is located within the observed narrow hystersis region.