SIMULATION OF FREE-ENERGY WITHOUT PARTICLE INSERTION IN THE NPT ENSEMBLE

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.