Waterlike structural and excess entropy anomalies in liquid beryllium fluoride

Abstract

The relationship between structural order metrics and the excess entropy is studied using the transferable rigid ion model (TRIM) of beryllium fluoride melt, which is known to display waterlike thermodynamic anomalies. The order map for liquid BeF₂, plotted between translational and tetrahedral order metrics, shows a structurally anomalous regime, similar to that seen in water and silica melt, corresponding to a band of state points for which average tetrahedral (q_tet) and translational (t) order are strongly correlated. The tetrahedral order parameter distributions further substantiate the analogous structural properties of BeF₂, SiO₂, and H₂O. A region of excess entropy anomaly can be defined within which the pair correlation contribution to the excess entropy (S₂) shows an anomalous rise with isothermal compression. Within this region of anomalous entropy behavior, qtetand S₂ display a strong negative correlation, indicating the connection between the thermodynamic and the structural anomalies. The existence of this region of excess entropy anomaly must play an important role in determining the existence of diffusional and mobility anomalies, given the excess entropy scaling of transport properties observed in many liquids.