The hierarchical reference theory as applied to square well fluids of variable range

Continuing our investigation into the numerical properties of the hierarchical reference theory, we study the square well fluid of range l from slightly above unity up to 3.6. After briefly touching upon the core condition and the related decoupling assumption necessary for numerical calculations, we shed some light on the way an inappropriate choice of the boundary condition imposed at high density may adversely affect the numerical results; we also discuss the problem of the partial differential equation becoming stiff for close-to-critical and subcritical temperatures. While agreement of the theory’s predictions with simulational and purely theoretical studies of the square well system is generally satisfactory for l*2, the combination of stiffness and the closure chosen is found to render the critical point numerically inaccessible in the current formulation of the theory for most of the systems with narrower wells. The mechanism responsible for some deficiencies is illuminated at least partially and allows us to conclude that the specific difficulties encountered for square wells are not likely to resurface for continuous potentials. © 2002 American Institute of Physics. @DOI: 10.1063/1.1483258#