Molecular dynamics studies of aromatic hydrocarbon liquids: Progress report, September 1986-February 1989

Molecular simulations are needed to model, develop, and test predictive methods for thermophysical properties of fluids of nonspherical molecules. In this regard, we have explored the idea of using pseudo-atomic potentials with particular emphasis on aromatic hydrocarbon liquids due to their importance in energy research. The use of a modified gaussian overlap pair potential to model aromatic rings has been examined and the resulting model is shown to work well for thermodynamic properties of liquid benzene and naphthalene and comparable to more complex potentials. The effect of molecule shape and electrostatics on thermodynamic properties in these liquids is also shown to be important. A first order thermodynamic perturbation theory and a sphericalized potential method have also been tested for these model potentials. These methods have been shown to be qualitative in their prediction of thermodynamic properties for the original gaussian overlap potential and quantitative, as well, for the modified gaussian overlap potential for one-site systems. Preliminary tests show these methods to be, at least, qualitative in their prediction of properties of a naphthalene-like fluid modeled using a gaussian overlap two-site potential and further studies are in progress. Simulations have also been carried out for liquid propane using three-site Lennard-Jones potentials. These, along with six-site simulations of benzene, clearly show the importance of locating the interaction sites if spheres are to be used in modeling CH, CH2, and CH3 groups in aromatic and aliphatic hydrocarbons. 61 refs., 23 figs., 5 tabs