Transitioning model potentials to real systems

The parameters of two pair potentials that describe argon over its entire l iquid phase at a fixed 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 tho se of a modified Lennard-Jones potential and a Lennard-Jones potential. The optimized potential determined using NPT-MD simulations reproduces experim ental densities, internal energies and enthalpies with an error less than 1 % over most of the liquid range and yields self-diffusion coefficients that are in excellent agreement with experiment. The results using the potentia l determined by NPT-MC simulations are in almost as good agreement with dev iations from experiment of no more than 5.89% for temperatures up to vapori zation. Additionally, molar volumes predicted using this potential at press ures 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 pro perly parametrized? Lennard-Jones-like potentials can describe a system wel l over a large temperature range. Further, the method introduced is easy to implement and is independent of the form of the interaction potential used .