Rational-function approximation for fluids interacting via piece-wise   constant potentials
  The structural properties of fluids whose molecules interact via potentials with a hard-core plus n piece-wise constant sections of different widths and heights are derived using a (semi-analytical) rational-function approximation method. The results are illustrated for the cases of a square-shoulder plus square-well potential and a shifted square-well potential and compared both with simulation data and with those that follow from the (numerical) solutions of the Percus-Yevick integral equation. 
A. Santos, S. B. Yuste, and M. L\'opez de Haro
cond-mat.soft cond-mat.stat-mech physics.chem-ph