Equation of state for the square-well chain fluid based on the dimer version of wertheim’s perturbation theory

An equation of state for the freely jointed square-well chain fluid developed using Wertheim’s thermodynamic perturbation theory and incorporating structural information on the square-well dimer fluid (TPT-D) is tested against the results of the Monte Carlo (MC) simulations. The performance of Wertheim’s first order thermodynamic perturbation theory (TPT1) and the TPT-D theory are evaluated using MC simulation results for the square-well monomers and square-well dimers to avoid introducing errors due to approximations in evaluating the thermodynamic properties of the reference fluids. The dimer version of Wertheim’s thermodynamic perturbation theory (TPT-D) increases the accuracy of the predicted value of compressibility factor of chain fluids in all ranges of density and temperature studied. To obtain the thermodynamic properties needed, N VT MC simulations were performed for the bulk phase of the square-well monomer, and for dimer, 4-mer, 8-mer and 16-mer square-well chain fluids. These MC simulation results are very accurate, and make possible a careful comparison between the TPT1 and TPT-D equations of state.