Density Anomaly in Core-Softened Lattice Gas
  A two dimensional lattice gas model with ''core-softened'' potential is investigated. Two liquid phases and density anomaly are found. The demixing phase transition between the two liquid phases end at a tricritical point that is also the terminus of a critical line. The density anomaly is related to this continuous line. 
Aline Lopes Balladares and Marcia C. Barbosa