Phase Transitions of the Classical Hard-Ellipse System

By Monte Carlo calculations in the canonical ensemble, we have studied some properties of a two-dimensional system of 170 long hard ellipses (whose axis ratio equals 6). This system can be considered as a two-dimensional model for a nematic liquid crystal. We have shown that this system exhibits two first-order phase transitions: a solid-nematic type phase transition at high density and a disorientation phase transition at a density 1.5 times smaller. This result suggests that excluded volume effects might play an essential role in the disorientation phase transition of nematic liquid crystals.