BREAKDOWN OF DIRECT RELATION BETWEEN DENSITY SCALING EXPONENT OF ROTATIONAL DYNAMICS AND INTERMOLECULAR INTERACTION POTENTIAL FOR MOLECULAR SYSTEMS WITH PURELY REPULSIVE INTERMOLECULAR FORCES

ABSTRACT The concept of density scaling, which perfectly works for many real van der Waals liquids and polymers, is examined for two quasi-real model systems to elucidate the origin of the density scaling exponent. Examined systems comprise the same purely repulsive atoms that interact via the potential of the inverse power law form that implies a perfect linear correlation between intermolecular virial and potential energy: the latter is expected to be a reason for the occurrence of the density scaling. However, the presented results indicate that the slope of that correlation does not correspond to the value of the density scaling exponent for the rotational dynamics. The proposed explanation of the problem focuses on the role of molecular anisotropy, meaning that, even for such simplified model systems, the effective intermolecular potential originating from all molecule’s atoms differs from the single atom–atom interaction potential. Consequently, we suggest that the density scaling exponent should refer to the complex, overall effective intermolecular potential; however, the weak point of this scenario is also pointed out.