RELATIVE STABILITY OF COLUMNAR AND CRYSTALLINE PHASES IN A SYSTEM OF PARALLEL HARD SPHEROCYLINDERS

We report a computer-simulation study of the stability of the columnar phase in a system of parallel spherocylinders with aspect ratios L/D = 5 and infinity. It is found that the range of stability of the columnar phase is strongly dependent upon the system size. In particular, for particles with an aspect ratio L/D = 5, the columnar phase that is observed in small systems (N = 90) disappears for a system of N = 1080 particles. In its place, a simple hexagonal crystal ("AAA stacking") appears. On the basis of our present simulations, we cannot tell whether the latter phase is truly crystalline or possibly a smectic-B phase. For particles with an aspect ratio L/D = infinity, similar behavior is observed, although in this case a stable columnar "pocket" remains, even for the largest systems we studied. We have computed the locations of all phase transitions involving the new hexagonal phase.