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How well does the Tang-Toennies potential represent the thermodynamic properties of argon?

Nitzke, Isabel; Pohl, Sven; Thol, Monika; Span, Roland; Vrabec, Jadran

FG Thermodynamik und Thermische Verfahrenstechnik

The potential function suggested by Tang and Toennies is parametrised to represent the thermodynamic properties of argon. The fit of its parameters is carried out on the basis of different data obtained by molecular dynamics simulation and integration of Mayer's f function. Apart from usual optimisation procedures, an efficient strategy based on reduced units is employed. The Tang-Toennies model with five adjustable parameters outperforms the Lennard-Jones model with only two parameters by far for the second virial coefficient. For other properties, the agreement with reference data is only slightly better. The critical point is still overestimated significantly. Since for pair potentials even a substantial increase of the number of parameters does not yield satisfying results, the only remedy is presumably the consideration of three-body interactions.