The Rise and Fall of Anomalies in Tetrahedral Liquids

Abstract

Abstract. 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.

Electrical conductivity of SiO 2 at extreme conditions and planetary dynamos

“…For example, in SiO2 liquid at low pressure, the liquid structure, characterized by almost perfect fourfold Si-O coordination at the lowest temperatures, shows increasing numbers of 5-and 3-coordinated Si on isochoric heating (27). The rate of structural change initially increases on heating, and then saturates, producing a local maximum in the heat capacity (32).…”

Triplet Correlations Dominate the Transition from Simple to Tetrahedral Liquids

“…Our motivation here is to understand the competition between pair and triplet correlations that underlies the transformation of a simple liquid into a complex, tetrahedral liquid, using the multiparticle correlation expansion for the entropy to translate the information on pair and triplet correlations into thermodynamic signatures associated with liquid state behavior and phase transformations [19][20][21][22][23][24]. As a model system, we use the Stillinger-Weber family of liquids that captures much of the complex phenomenology of tetrahedral liquids, especially with regard to water and silicon [5,[15][16][17][18][25][26][27][28][29][30]. We show that as a function of tetrahedrality, the liquid state can be subdivided into pair-and triplet-dominated regimes, separated by a narrow, glassforming region where orientational disorder within the first neighbor shell is significant.…”

“…They show a density-driven shift from four-coordinate, local order at low densities to random, close-packing arrangements at high densities. Depending on the degree of energetic preference for local tetrahedral order, they display several differences in comparison to simple liquids, including density and related response function anomalies, negative volume changes on melting, crystalline polymorphism, and polyamorphism [10,[14][15][16][17][18]. Our motivation here is to understand the competition between pair and triplet correlations that underlies the transformation of a simple liquid into a complex, tetrahedral liquid, using the multiparticle correlation expansion for the entropy to translate the information on pair and triplet correlations into thermodynamic signatures associated with liquid state behavior and phase transformations [19][20][21][22][23][24].…”

“…The parameter values were A ¼ 7.049556277, [18]. Computational details are given in the Supplemental Material [36].…”

How Short Is Too Short for the Interactions of a Water Potential? Exploring the Parameter Space of a Coarse-Grained Water Model Using Uncertainty Quantification

“…42,47,48,68,69 We constructed response surfaces using the interpolating polynomials described in eqs 9 and 12 to determine the output properties of ΔH vap and ρ as a function of the parameters. The interpolating polynomials were generated from the basis set of observations from the 729 simulations that spanned the parameter space (ε, σ, λ).…”