  The osmotic equation of state for the athermal bond fluctuation model on the
simple cubic lattice is obtained from extensive Monte Carlo simulations. For
short macromolecules (chain length N=20) we study the influence of various
choices for the chain stiffness on the equation of state. Three techniques are
applied and compared in order to critically assess their efficiency and
accuracy: the repulsive wall method, the thermodynamic integration method
(which rests on the feasibility of simulations in the grand canonical
ensemble), and the recently advocated sedimentation equilibrium method, which
records the density profile in an external (e.g. gravitation-like) field and
infers, via a local density approximation, the equation of state from the
hydrostatic equilibrium condition. We confirm the conclusion that the latter
technique is far more efficient than the repulsive wall method, but we find
that the thermodynamic integration method is similarly efficient as the
sedimentation equilibrium method. For very stiff chains the onset of nematic
order enforces the formation of isotropic-nematic interface in the
sedimentation equilibrium method leading to strong rounding effects and
deviations from the true equation of state in the transition regime.
