The Wilson

NRTL

UNIQUAC

and Wang - Chao activity coefficient models have been investigated in terms of the GE data from the Monte Carlo simulation carried out by the authors. In this investigation

several expressions for different local composition and coordination number definitions have been tested. Molecular parameters for the Lennard -Jones fluids have been introduced to each model to clarify the influences of the variables

including molecule size

interaction energy

composition

temperature

and pressure. As a result

analysis on the molecular assumptions and inherent shortcomings for these activity coefficient models provides a guidance for their improvement.