Structural anomalies of fluids: Origins in second and higher coordination shells

Abstract

Compressing or cooling a fluid typically enhances its static interparticle correlations. However, there are notable exceptions. Isothermal compression can reduce the translational order of fluids that exhibit anomalous waterlike trends in their thermodynamic and transport properties, while isochoric cooling (or strengthening of attractive interactions) can have a similar effect on fluids of particles with short-range attractions. Recent simulation studies by Yan et al. [Phys. Rev. E 76, 051201 (2007)] on the former type of system and Krekelberg et al. [J. Chem. Phys. 127, 044502 (2007)] on the latter provide examples where such structural anomalies can be related to specific changes in second and more distant coordination shells of the radial distribution function. Here, we confirm the generality of this microscopic picture through analysis, via molecular simulation and integral equation theory, of coordination shell contributions to the two-body excess entropy for several related model fluids which incorporate different levels of molecular resolution. The results suggest that integral equation theory can be an effective and computationally inexpensive first-pass tool for assessing, based on the pair potential alone, whether new model systems are good candidates for exhibiting structural (and hence thermodynamic and transport) anomalies.

Softness dependence of the anomalies for the continuous shouldered well potential

“…60 we perform an analysis of the excess entropy shell by shell, but instead of calculating only the cumulative order integral, as in Ref. 60 ,…”

Diffusion enhancement in core-softened fluid confined in nanotubes

“…Examples are solvation and properties which depend on polarization. On the other hand, the literature have many examples in which systems with absence of anisotropic interactions still may present some of the water features [17][18][19][20][21][22][23][24][25][26][27][28] .…”

“…From the desire of constructing a simple two-body potential capable of describing the anomalous behavior of bulk water, a number of models have been developed [17][18][19][20][21][22][23][24][25][26][27][28] . Despite their simplicity, such models had successfully reproduced the thermodynamic, dynamic, and structural anomalous behavior present in bulk liquid water.…”

Phase Diagram and Waterlike Anomalies in Core-Softened Shoulder-Dumbbell Complex Fluids

“…The scientific community has already recognized that such big challenge demands a smart strategy: beginning with the simplest models. It is recognized that the origin of the anomalies is related to the competition between open low-density and closed high-density structures, which depend on the thermodynamic state of the liquid (Krekelberg et al, 2008). In simple isotropic models, this competition is described by two preferred interparticle distances.…”

“…the loci in the pressure-temperature phase diagram of the state points displaying anomalous behavior (de Oliveira et al, 2006a;b), is the same as in water (Errington & Debenedetti, 2001;Netz et al, 2001): the structurally anomalous region in the pressure-temperature phase diagram enclosing the region of dynamic (diffusivity) anomalies, that in its turn is enclosing region of the thermodynamic (density) anomalies. In principle this shoulder potential can represent in an effective and orientation-averaged way the interaction between water pentamers (Krekelberg et al, 2008) characterized by the presence of two structures -one open and one closed -as discussed above. Similarly, the thermodynamic and dynamic anomalies result from the competition between the two length scales associated with the open and closed structures.…”