The parameters of two pair potentials that describe argon over its entire liquid phase at a ® xed pressure were optimized through a novel application of constant temperature and pressure molecular dynamics (NPT -MD) and Monte Carlo (NPT -MC) computer simulations. The forms of these potentials were those of a modi® ed Lennard-Jones potential and a Lennard-Jones potential. The optimized potential determined using NPT -MD simulations reproduces experimental densities, internal energies and

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... es with an error less than 1% over most of the liquid range and yields self-di usion coe cients that are in excellent agreement with experiment. The results using the potential determined by NPT -MC simulations are in almost as good agreement with deviations from experiment of no more than 5.89% for temperatures up to vaporization. Additionally, molar volumes predicted using this potential at pressures in the range 100± 600 atm and over temperatures in the range 100± 140 K were within 0.83% of experimental values. These results show that, when properly parametrized, Lennard-Jones-like potentials can describe a system well over a large temperature range. Further, the method introduced is easy to implement and is independent of the form of the interaction potential used.