Exact solution of the Percus-Yevick integral equation for collapsing   hard spheres
  By Wertheim-method the exact solution of the Percus-Yevick integral equation for a system of particles with the repulsive step potential interacting (collapsing hard spheres) is obtained. On the basis of this solution the state equation for the repulsive step potential is built and determined, that the Percus-Yevick equation does not show phase transition for collapsing hard spheres. 
I.Klebanov, P. Gritsay, N. Ginchitskii