Mean spherical approximation and optimized cluster theory for the square-well fluid

The mean spherical approximation and the related optimized cluster theory are applied to the square-well fluid with a well width of 0.5σ, where σ is the hard-sphere diameter. The resulting equations of state and radial distribution functions are determined numerically and compared both with computer simulation results and with previously reported Percus–Yevick and hyper-netted chain theory calculations. In general, the mean spherical approximation results are more accurate than those of the optimized cluster theory. This is especially true if the energy equation is used. Both approximations are more accurate than the Percus–Yevick and hyper-netted chain approximations.