Thermodynamic and Structural Characterization of the Transformation from a Metastable Low‐Density to a Very High‐Density Form of Supercooled TIP4P‐Ew Model Water

Paschek, Dietmar; Rüppert, Andreas; Geiger, Alfons

doi:10.1002/cphc.200800539

Cited by 58 publications

(42 citation statements)

References 39 publications

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“…It would be logical to conclude that the SPC/E model is incapable of getting sensible values of Sð0Þ and reproducing SAXS data at room temperature, and hence that failure would likely be because it is not tetrahedral enough. Paschek and coworkers have recently characterized the phase diagram of TIP4P-Ew, and found that the model "almost quantitatively matches the (experimental) compressibility and thermal expansivity of water up to pressures in the gigapascal range" (37). The TIP4P-Ew model also reproduces a minimum in SðQÞ and correlation lengths that are small which remain constant with temperature-consistent with the published small angle scattering (SAS) experiments on water taken at third generation synchrotron sources.…”

Section: Discussionsupporting

confidence: 58%

Small-angle scattering and the structure of ambient liquid water

Clark

Hura²,

Teixeira³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

191

184

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Structural polyamorphism has been promoted as a means for understanding the anomalous thermodynamics and dynamics of water in the experimentally inaccessible supercooled region. In the metastable liquid region, theory has hypothesized the existence of a liquid-liquid critical point from which a dividing line separates two water species of high and low density. A recent smallangle X-ray scattering study has claimed that the two structural species postulated in the supercooled state are seen to exist in bulk water at ambient conditions. We analyze new small-angle X-ray scattering data on ambient liquid water taken at third generation synchrotron sources, and large 32,000 water molecule simulations using the TIP4P-Ew model of water, to show that the small-angle region measures standard number density fluctuations consistent with water's isothermal compressibility temperature trends. Our study shows that there is no support or need for heterogeneities in water structure at room temperature to explain the small-angle scattering data, as it is consistent with a unimodal density of the tetrahedral liquid at ambient conditions. anomalous scattering | density distribution | isothermal compressibility | structural polyamorphism W ater appears to be a unique liquid relative to other fluids in exhibiting several anomalous features of structure, thermodynamics, and dynamics. Both experiment and molecular dynamics simulation have shown that water in the metastable supercooled region exhibits response functions and transport properties that appear to diverge near −45°C (1). Below its glass transition temperature, experimental evidence shows that there are polyamorphic states of water, in particular the formation of low-density amorphous and high-density amorphous glasses (2, 3). This polyamorphism has been promoted as a means for understanding the anomalous thermodynamics and dynamics of water, such as the large increase in its isothermal compressibility with decreasing temperature, when extrapolated into the experimentally inaccessible supercooled liquid region (3, 4). Polyamorphism underlies one of the main assumptions of the second critical point hypothesis (5), i.e., the postulated existence of a liquid-liquid critical point from which a dividing line separates two fluctuating species of high and low-density liquids (HDL and LDL).However, recent studies have shown that while there may be low-temperature criticality in the ST2 water model, there is no need to invoke an explanation for a second critical point in water based on structural polyamorphism (6). Furthermore, it is also possible to explain the existing anomalies without invoking an additional thermodynamic singularity, in the so-called singularityfree interpretation (4, 7). Sastry and coworkers have shown that a finite increase in isothermal compressibility upon lowering the temperature of a liquid that expands upon cooling (like water) is a thermodynamic necessity, and was illustrated for a water-like lattice model that has no singularities (7). This diversity in ...

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Section: Discussionsupporting

confidence: 58%

Small-angle scattering and the structure of ambient liquid water

Clark

Hura²,

Teixeira³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

191

184

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“…[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] Detailed studies using ST2-RF have been made by Poole et al 56 using molecular dynamics, while Liu et al 57,58 simulated ST2 with Ewald summation (ST2-Ew) for the electrostatic long-range potential using Monte Carlo. Also in other water models the LLPT and its LLCP are believed to be found, for example, by Yamada et al 59 in the TIP5P model, by Paschek et al 60 in the TIP4P-Ew model, and in TIP4P/2005 by Abascal and Vega. 61,62 Recently, Limmer and Chandler 63 used Monte Carlo umbrella sampling to investigate the ST2-Ew model, but claimed to have found only one liquid metastable phase (HDL) rather than two.…”

Section: Introductionmentioning

confidence: 85%

Finite-size scaling investigation of the liquid-liquid critical point in ST2 water and its stability with respect to crystallization

Kesselring

Lascaris

Franzese

et al. 2013

The Journal of Chemical Physics

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The liquid-liquid critical point scenario of water hypothesizes the existence of two metastable liquid phases-low-density liquid (LDL) and high-density liquid (HDL)-deep within the supercooled region. The hypothesis originates from computer simulations of the ST2 water model, but the stability of the LDL phase with respect to the crystal is still being debated. We simulate supercooled ST2 water at constant pressure, constant temperature, and constant number of molecules N for N ≤ 729 and times up to 1 μs. We observe clear differences between the two liquids, both structural and dynamical. Using several methods, including finite-size scaling, we confirm the presence of a liquid-liquid phase transition ending in a critical point. We find that the LDL is stable with respect to the crystal in 98% of our runs (we perform 372 runs for LDL or LDL-like states), and in 100% of our runs for the two largest system sizes (N = 512 and 729, for which we perform 136 runs for LDL or LDL-like states). In all these runs, tiny crystallites grow and then melt within 1 μs. Only for N ≤ 343 we observe six events (over 236 runs for LDL or LDL-like states) of spontaneous crystallization after crystallites reach an estimated critical size of about 70 ± 10 molecules. © 2013 AIP Publishing LLC. [http://dx

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“…While the main contesting thermodynamic scenarios are the liquid-liquid critical-point (LLCP) 12 , the singularity-free (SF) 13 , the critical-point free (CPF) 14 and the stability-limit (SL) hypothesis 15 , most molecular dynamics (MD) force-fields seem to exhibit one or more critical points in the deeply supercooled liquid region, e.g., refs. 12,[16][17][18][19][20] , and thus support the LLCP scenario. All four scenarios were unified in a single Hamiltonian cell-model 21 where two key parameters of molecular interactions in water, the cooperative and the directional components of the H-bond interaction, could be tuned to obtain phase diagrams corresponding to each scenario.…”

Section: Introductionmentioning

confidence: 90%

Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water

Huang

Wikfeldt

Nordlund

et al. 2011

Phys. Chem. Chem. Phys.

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We have developed x-ray diffraction measurements with high energy-resolution and accuracy to study water structure at three different temperatures (7, 25 and 66 C) under normal pressure. Using a spherically curved Ge crystal an energy resolution better than 15 eV has been achieved which eliminates influence from Compton scattering. The high quality of the data allows a precise oxygen-oxygen pair correlation function (PCF) to be directly derived from the Fourier transform of the experimental data resolving shell structure out to ~12 Å, i.e. 5 hydration shells. Large-scale molecular dynamics (MD) simulations using the TIP4P/2005 force-field reproduce excellently the experimental shell-structure in the range 4-12 Å although less agreement is seen for the first peak in the PCF. The Local Structure Index [J. Chem. Phys. 104, 7671 (1996)] identifies a tetrahedral minority giving the intermediate-range oscillations in the PCF and a disordered majority providing a more featureless background in this range. The current study supports the proposal that the structure of liquid water, even at high temperatures, can be described in terms of a two-state fluctuation model involving local structures related to the high-density and low-density forms of liquid water postulated in the liquid-liquid phase transition hypothesis.

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Thermodynamic and Structural Characterization of the Transformation from a Metastable Low‐Density to a Very High‐Density Form of Supercooled TIP4P‐Ew Model Water

Cited by 58 publications

References 39 publications

Small-angle scattering and the structure of ambient liquid water

Small-angle scattering and the structure of ambient liquid water

Finite-size scaling investigation of the liquid-liquid critical point in ST2 water and its stability with respect to crystallization

Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water

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