Molecular structural order and anomalies in liquid silica

Abstract

The present investigation examines the relationship between structural order, diffusivity anomalies, and density anomalies in liquid silica by means of molecular dynamics simulations. We use previously defined orientational and translational order parameters to quantify local structural order in atomic configurations. Extensive simulations are performed at different state points to measure structural order, diffusivity, and thermodynamic properties. It is found that silica shares many trends recently reported for water [J. R. Errington and P. G. Debenedetti, Nature 409, 318 (2001)]. At intermediate densities, the distribution of local orientational order is bimodal. At fixed temperature, order parameter extrema occur upon compression: a maximum in orientational order followed by a minimum in translational order. Unlike water, however, silica's translational order parameter minimum is broad, and there is no range of thermodynamic conditions where both parameters are strictly coupled. Furthermore, the temperature-density regime where both structural order parameters decrease upon isothermal compression (the structurally anomalous regime) does not encompass the region of diffusivity anomalies, as was the case for water.

Wang-Landau sampling of an asymmetric ising model: a study of the critical endpoint behavior

“…For example, this method has been used in studies of a Potts antiferromagnet [12], random spin systems [13], quantum systems [14][15][16], fluids [17,18], binary Lennard-Jones glass [19], liquid crystals [20], polymers [17,21], proteins [22,23], other molecular systems [24,25], atomic clusters [26], optimization problems [27], and combinatorial number theory [28]. Generalizations and further studies of this sampling technique have also been carried out by several authors [29][30][31][32][33].…”

Thermodynamic properties and correlation functions of Ar films on the surface of a bundle of nanotubes

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Critical points, phase transitions and water-like anomalies for an isotropic two length scale potential with increasing attractive well

“…The structural properties of the fluid were obtained by inspection of the behavior of the translation order parameter [13][14][15], defined as…”

“…While for normal liquids the system becomes more structured with the increase of the density, water shows a maximum. Such behavior can be characterized by translational order parameter t [13][14][15] that exhibits a region in which t decreases under compression. The entropy also shows a very peculiar behavior.…”

“…Studies have shown that Te [27], Ga, Bi [28], S [29,30], Ge 15 Te 85 [31], BeF 2 [16,[32][33][34], silica [13,16,32,35] and silicon [36] present water-like anomalies.…”