Supercooled fluid-fluid phase transition in three dimensions from a   soft-core potential
  To study the possibility of a fluid-fluid phase transition, we analyze a three-dimensional soft-core isotropic potential for a one-component system. We utilize two independent numerical approaches, (i) integral equation in the hypernetted-chain approximation and (ii) molecular dynamics simulations, and find for both approaches a fluid-fluid phase transition as well as the conventional gas-liquid critical point. We also study the possible existence of a triple point in the supercooled fluid phase at which three phases---gas, high-density fluid, and low-density fluid---coexist. 
G. Franzese, G. Malescio, A. Skibinsky, S. V. Buldyrev, and H. E.   Stanley