Tetrahedral order, pair correlation entropy, and waterlike liquid state anomalies: Comparison of GeO2 with BeF2, SiO2, and H2O

Molecular dynamics simulations of the Oeffner-Elliot model of germania (GeO2) are performed to identify nested regions of anomalous behavior in structural order, diffusivity, and pair entropy in the density-temperature plane, analogous to that seen in BeF2, SiO2, and H2O. The decreasing constraint of local tetrahedrality in GeO2, compared to SiO2 and BeF2, substantially lowers the onset temperatures for anomalous behavior relative to the experimental melting temperatures (T-m). Germania resembles water, more strongly than the ionic melts, in terms of temperatures for onset of anomalous behavior as well as in the order maps; for example, the structural anomaly sets in at 3.42T(m) in BeF2, 3.09T(m) in SiO2, 1.43T(m) in GeO2, and 1.21T(m) in H2O. The detailed shapes of the anomalous regimes vary for different systems but the relative temperatures of onset for different anomalies are very similar in the different systems. The pair correlation entropy is shown to be a crucial and experimentally accessible quantity for relating structure, entropy, and diffusivity that could be potentially useful for a large class of inorganic ionic liquids. (C) 2010 American Institute of Physics. [doi:10.1063/1.3439593]