  The thermodynamic liquid-state anomalies and associated structural changes of
the Stillinger-Weber family of liquids are mapped out as a function of the
degree of tetrahedrality of the interaction potential, focusing in particular
on tetrahedrality values suitable for modeling C, H2O, Si, Ge and Sn. We show
that the density anomaly, associated with a rise in molar volume on isobaric
cooling, emerges at intermediate tetrahedralities (e.g. Ge, Si and H2O) but is
absent in the low (e.g. Sn) and high (e.g. C) tetrahedrality liquids. The rise
in entropy on isothermal compression associated with the density anomaly is
related to the structural changes in the liquid using the pair correlation
entropy. An anomalous increase in the heat capacity on isobaric cooling exists
at high tetrahedralities but is absent at low tetrahedralities (e.g. Sn).
Structurally, this heat capacity anomaly originates in a sharp rise in the
fraction of four-coordinated particles and local tetrahedral order in the
liquid as its structure approaches that of the tetrahedral crystal.
