A temperature perturbation method for a direct Monte Carlo simulation
of the residual free energy is extended to the isothermal-isobaric ens
emble. Unlike many other free energy or phase equilibrium methods, par
ticle insertion is avoided. At the same time, the usual Boltzmann samp
ling is maintained. The results show excellent agreement with equation
s of state and thermodynamic integration for fluids of hard dumbbells
and linear chains of tangent hard spheres. The results cover states at
which insertion techniques fail.