Dr. Hajime Tanaka's research group have shown through simulation that four phases of a substance composed of a single component can coexist at thermal equilibrium―where all parts are at the same temperature and pressure― a situation that runs counter to the laws of thermodynamics (as stated in the Gibbs phase rule). The findings not only deepen our basic understanding of phases of a substance existing in equilibrium, but they also may be applied to the development of functional materials possessing phase-change properties.