Polymorphism, thermodynamic anomalies, and network formation in an atomistic model with two internal states.

Using molecular dynamics simulations we study, in two dimensions, the temperature-density phase diagram of a simple model with two internal states labeled 1 and -1. The particles interact with a modified Lennard-Jones potential, which depends on relative positions of the particles as well as on their state. Working in an ensemble where the system reduces to a 50:50 binary mixture of two species of particles, we obtain a rich phase diagram showing many features of common network-forming liquids such as water and silica, including polymorphism and thermodynamic anomalies. We believe our model may be useful for studies concerning generic features of such complex liquids.