Model interactions for liquid systems with tetrahedral local coordination

Tetrahedral liquids, i.e. liquids characterized by tetrahedral local order, are an important class of systems for biological, technological and fundamental reasons. They exhibit a number of behaviors that are anomalous with respect to those of simple, spherically symmetric, liquids. The ability to design suitable model interactions for such systems is crucial in understanding their peculiar features. Modelling tetrahedral liquids may proceed along two different, but complementary, directions: designing models able to describe real interactions as accurately as possible, or finding simple interactions that are nevertheless able to qualitatively reproduce the anomalous behaviors characterizing such systems. Here we review the most significant examples of both approaches and discuss how these have made it possible to reach a better comprehension of tetrahedral liquids.