Evidence for one-, two-, and three-dimensional order in a system of hard parallel spherocylinders.

Abstract

The phase diagram of a system of hard parallel spherocylinders with length-to-width ratios L/D between 0 and ∞ is investigated by Monte Carlo simulation. In addition to a low-density nematic phase and a high-density crystalline phase, two phases with partial translational order are observed, viz., a smectic phase and a columnar phase. By computing the absolute free energy of all phases, their range of stability and coexistence points are determined. For L/D ratios exceeding 0.5, a stable smectic phase is formed at densities well below the thermodynamic melting point. The nematic-to-smectic transition appears to be continuous. A columnar phase is only observed for L/D>3 at densities intermediate between the smectic and crystalline phases. The smectic-to-columnar transition is first order for L/D≤5. In the limit L/D→∞ this transition becomes continuous.