Isotherms of exptl. data of internal pressure of dense fluids vs. molar volume, V m are shown to have each a max. point at a Vmax below the crit. molar volume. We investigated the role of attractive and repulsive intermol. energies on this behavior using a mol. dynamics simulation technique. In the simulation, we choose the Lennard-Jones (LJ) intermol. potential energy function. The LJ potential is known to be an effective potential representing a statistical av. of the true pair and many-body interactions in simple mol. systems. The LJ potential function is divided into attractive and repulsive parts. MD calcns. have produced internal energy, potential energy, transitional kinetic energy, and radial distribution function (RDF) for argon at 180 K and 450 K using LJ potential, LJ repulsive, and LJ attractive parts. The LJ potential function is well capable of predicting the inflection point in the internal energy-molar volume curve as well as max. point in the internal pressure-molar volume curve. At molar volumes higher than V max, the attractive forces have strong influence on detn. of internal energy and internal pressure. At vols. lower than Vmax, neither repulsive nor attractive forces are dominating. Also, the coincidence between RDFs resulting from LJ potential and repulsive parts of LJ potential improves as molar volume approaches Vmax from high molar volumes. The coincidence becomes complete at Vmax  V.

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