Gibbs ensemble simulation of nematic-isotropic coexistence in a liquid crystal mixture

The results are presented of Gibbs ensemble Monte Carlo (GEMC) simulations examining the nematic-isotropic (N-I) coexistence envelope of a liquid crys tal mixture. The system studied is a 50: 50 mixture of 1000 generalized Gay -Berne particles with axial ratios 2.0:1 and 2.5:1. For this system, stable N-I coexistence is observed over run lengths in excess of 5 x 10(5) GEMC s weeps. There is unambiguous evidence of fractionation, the mole fractions o f long particles in the coexisting phases typically differing by 11%. The m easured coexistence envelope does not conform to the lens shape predicted b y Onsager theory; qualitative finite size arguments are given in explanatio n of this distortion.