  The isotropic to nematic transition in a system of soft spherocylinders is
studied by means of grand canonical Monte Carlo simulations. The probability
distribution of the particle density is used to determine the coexistence
density of the isotropic and the nematic phases. The distributions are also
used to compute the interfacial tension of the isotropic--nematic interface,
including an analysis of finite size effects. Our results confirm that the
Onsager limit is not recovered until for very large elongation, exceeding at
least L/D=40, with L the spherocylinder length and D the diameter. For smaller
elongation, we find that the interfacial tension increases with increasing L/D,
in agreement with theoretical predictions.
