irial coefficients and inversion curve of simple and associating fluids

Free energy simulation method is applied to calculate the virial coefficients of square-well (SW) fluids of variable well-width and square-well based dimer forming associating fluids. In this approach, Monte Carlo sampling is performed on a number of molecules equal to the order of integral, and configurations are weighted according to the absolute value of the integrand. An umbrella-sampling average yields the value of the cluster integral in reference to a known integral. By using this technique, we determine the virial coefficients up to B6 for SW fluid with variable potential range from =1.25 to =3.0 and model associating fluidswith different association strengths: εaf = 0.0, 8.0, 16.0 and 22.0. These calculated values