Short range orientational order in nematic liquid crystals

The different approximations that have been used in applying Bethe's cluster model to the nematic-isotropic phase transition are examked. It is shown that the introduction of a higher order term in the mean field potentialof an outer molecule of the cluster improves the consistency of the theory considerably. In particular, the importance of satisfying Chang's relation is emphasizec'. Calculations are presented of the long and short range order parameters, heat of transi- tion and specific heat for different values of z, the number of nearest neighbours around any given molecule, for both nonpolar and antiparallel near nright'ur correlations. Even the new mean field potential appears to be icadeq~ate fc 1 Z= 3