Publications by year, excluding conference proceedings.
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2019
Giovambattista, Nicolas; Starr, Francis W; Poole, Peter H
State variables for glasses: The case of amorphous ice Journal Article
In: The Journal of Chemical Physics, vol. 150, no. 22, pp. 224502, 2019.
Abstract | BibTeX | Tags: Glass Formation, Water | Links:
@article{gsp19,
title = {State variables for glasses: The case of amorphous ice},
author = {Nicolas Giovambattista and Francis W Starr and Peter H Poole},
url = {http://fstarr.web.wesleyan.edu/publications/gsp19.pdf},
doi = {10.1063/1.5092586},
year = {2019},
date = {2019-06-10},
journal = {The Journal of Chemical Physics},
volume = {150},
number = {22},
pages = {224502},
abstract = {Glasses are out-of-equilibrium systems whose state cannot be uniquely defined by the usual set of equilibrium state variables. Here, we seek to identify an expanded set of variables that uniquely define the state of a glass. The potential energy landscape (PEL) formalism is a useful approach within statistical mechanics to describe supercooled liquids and glasses. We use the PEL formalism and computer simulations to study the transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA). We employ the ST2 water model, which exhibits an abrupt first-order-like phase transition from LDA to HDA, similar to that observed in experiments. We prepare a number of distinct samples of both LDA and HDA that have completely different preparation histories. We then study the evolution of these LDA and HDA samples during compression and decompression at temperatures sufficiently low that annealing is absent and also during heating. We find that the evolution of each glass sample, during compression/decompression or heating, is uniquely determined by six macroscopic properties of the initial glass sample. These six quantities consist of three conventional thermodynamic state variables, the number of molecules N, the system volume V, and the temperature T, as well as three properties of the PEL, the inherent structure (IS) energy EIS, the IS pressure PIS, and the average curvature of the PEL at the IS ?IS. In other words, (N,V,T,EIS,PIS,?IS) are state variables that define the glass state in the case of amorphous ice. An interpretation of our results in terms of the PEL formalism is provided. Since the behavior of water in the glassy state is more complex than for most substances, our results suggest that these six state variables may be applicable to amorphous solids in general and that there may be situations in which fewer than six variables would be sufficient to define the state of a glass.},
keywords = {Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
Glasses are out-of-equilibrium systems whose state cannot be uniquely defined by the usual set of equilibrium state variables. Here, we seek to identify an expanded set of variables that uniquely define the state of a glass. The potential energy landscape (PEL) formalism is a useful approach within statistical mechanics to describe supercooled liquids and glasses. We use the PEL formalism and computer simulations to study the transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA). We employ the ST2 water model, which exhibits an abrupt first-order-like phase transition from LDA to HDA, similar to that observed in experiments. We prepare a number of distinct samples of both LDA and HDA that have completely different preparation histories. We then study the evolution of these LDA and HDA samples during compression and decompression at temperatures sufficiently low that annealing is absent and also during heating. We find that the evolution of each glass sample, during compression/decompression or heating, is uniquely determined by six macroscopic properties of the initial glass sample. These six quantities consist of three conventional thermodynamic state variables, the number of molecules N, the system volume V, and the temperature T, as well as three properties of the PEL, the inherent structure (IS) energy EIS, the IS pressure PIS, and the average curvature of the PEL at the IS ?IS. In other words, (N,V,T,EIS,PIS,?IS) are state variables that define the glass state in the case of amorphous ice. An interpretation of our results in terms of the PEL formalism is provided. Since the behavior of water in the glassy state is more complex than for most substances, our results suggest that these six state variables may be applicable to amorphous solids in general and that there may be situations in which fewer than six variables would be sufficient to define the state of a glass.
2017
Giovambattista, Nicolas; Starr, Francis W.; Poole, Peter H.
Influence of sample preparation on the transformation of low-density to high-density amorphous ice: An explanation based on the potential energy landscape Journal Article
In: The Journal of Chemical Physics, vol. 147, no. 4, pp. 044501, 2017.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{gsp17,
title = {Influence of sample preparation on the transformation of low-density to high-density amorphous ice: An explanation based on the potential energy landscape},
author = {Nicolas Giovambattista and Francis W. Starr and Peter H. Poole},
url = {http://fstarr.web.wesleyan.edu/publications/gsp17.pdf},
doi = {10.1063/1.499356},
year = {2017},
date = {2017-07-25},
journal = {The Journal of Chemical Physics},
volume = {147},
number = {4},
pages = {044501},
abstract = {Experiments and computer simulations of the transformations of amorphous ices display different behaviors depending on sample preparation methods and on the rates of change of temperature and pressure to which samples are subjected. In addition to these factors, simulation results also depend strongly on the chosen water model. Using computer simulations of the ST2 water model, we study how the sharpness of the compression-induced transition from low-density amorphous ice (LDA) to high-density amorphous ice (HDA) is influenced by the preparation of LDA. By studying LDA samples prepared using widely different procedures, we find that the sharpness of the LDA-to-HDA transformation is correlated with the depth of the initial LDA sample in the potential energy landscape (PEL), as characterized by the inherent structure energy. Our results show that the complex phenomenology of the amorphous ices reported in experiments and computer simulations can be understood and predicted in a unified way from knowledge of the PEL of the system.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
Experiments and computer simulations of the transformations of amorphous ices display different behaviors depending on sample preparation methods and on the rates of change of temperature and pressure to which samples are subjected. In addition to these factors, simulation results also depend strongly on the chosen water model. Using computer simulations of the ST2 water model, we study how the sharpness of the compression-induced transition from low-density amorphous ice (LDA) to high-density amorphous ice (HDA) is influenced by the preparation of LDA. By studying LDA samples prepared using widely different procedures, we find that the sharpness of the LDA-to-HDA transformation is correlated with the depth of the initial LDA sample in the potential energy landscape (PEL), as characterized by the inherent structure energy. Our results show that the complex phenomenology of the amorphous ices reported in experiments and computer simulations can be understood and predicted in a unified way from knowledge of the PEL of the system.
Rivera, Jose L.; Villanueva-Mejia, Francisco; Navarro-Santos, Pedro; Starr, Francis W.
Desalination by dragging water using a low-energy nano-mechanical device of porous graphene Journal Article
In: RSC Adv., vol. 7, pp. 53729-53739, 2017.
Abstract | BibTeX | Tags: Nanotechnology, Thin Films, Water | Links:
@article{rvns17,
title = {Desalination by dragging water using a low-energy nano-mechanical device of porous graphene},
author = { Jose L. Rivera and Francisco Villanueva-Mejia and Pedro Navarro-Santos and Francis W. Starr},
url = {http://fstarr.web.wesleyan.edu/publications/rvns17.pdf},
doi = {10.1039/C7RA09847B},
year = {2017},
date = {2017-01-01},
journal = {RSC Adv.},
volume = {7},
pages = {53729-53739},
publisher = {The Royal Society of Chemistry},
abstract = {We propose a nano-structured suction system based on graphene sheets for water desalination processes. The desalination system modeled in this work is an alternative process to the commonly employed but energy intensive reverse osmosis process. The nano-structured system generates drag forces, which pull water molecules from the saline solution into a chamber. Our molecular simulations consist of two rigid walls of graphene: one wall with 5 A pores permeable to water molecules forms the membrane, while the other wall acts as a plunger to induce and control the transfer of desalinated water molecules, which accumulate in a chamber between the two walls. Prior to the desalination process, the chamber is saturated with one monolayer of water molecules. The desalination occurs when the plunger moves to create unsaturated space inside the chamber. At plunger speeds up to 10 cm s-1, the system desalinates saltwater films in the open part of the membrane. At higher plunger speeds, the desalination chamber expands faster than molecules can fill the chamber, resulting in cavitation and poor desalination. At plunger speeds of 0.5 cm s-1, the desalination occurs via a quasi-equilibrium process, which minimizes the energy necessary to drive desalination. Our findings suggest that the desalination process requires less energy than reverse osmosis methods at plunger speeds up to 0.15 cm s-1 (for the chosen pore density). The filling profile of desalinated water molecules inside the chamber occurs via three distinct regimes: the first two regimes correspond to the formation of one and then two monolayers adsorbed to the chamber's walls. The third regime corresponds to the filling of molecules between the adsorbed layers, which approaches a density close to the density of bulk liquid water. Including flexibility in the graphene sheets does not affect the energy consumption for desalination processes occurring after the formation of the second monolayer, but flexible membranes require a slightly larger pore diameter (7 A) than rigid membranes.},
keywords = {Nanotechnology, Thin Films, Water},
pubstate = {published},
tppubtype = {article}
}
We propose a nano-structured suction system based on graphene sheets for water desalination processes. The desalination system modeled in this work is an alternative process to the commonly employed but energy intensive reverse osmosis process. The nano-structured system generates drag forces, which pull water molecules from the saline solution into a chamber. Our molecular simulations consist of two rigid walls of graphene: one wall with 5 A pores permeable to water molecules forms the membrane, while the other wall acts as a plunger to induce and control the transfer of desalinated water molecules, which accumulate in a chamber between the two walls. Prior to the desalination process, the chamber is saturated with one monolayer of water molecules. The desalination occurs when the plunger moves to create unsaturated space inside the chamber. At plunger speeds up to 10 cm s-1, the system desalinates saltwater films in the open part of the membrane. At higher plunger speeds, the desalination chamber expands faster than molecules can fill the chamber, resulting in cavitation and poor desalination. At plunger speeds of 0.5 cm s-1, the desalination occurs via a quasi-equilibrium process, which minimizes the energy necessary to drive desalination. Our findings suggest that the desalination process requires less energy than reverse osmosis methods at plunger speeds up to 0.15 cm s-1 (for the chosen pore density). The filling profile of desalinated water molecules inside the chamber occurs via three distinct regimes: the first two regimes correspond to the formation of one and then two monolayers adsorbed to the chamber's walls. The third regime corresponds to the filling of molecules between the adsorbed layers, which approaches a density close to the density of bulk liquid water. Including flexibility in the graphene sheets does not affect the energy consumption for desalination processes occurring after the formation of the second monolayer, but flexible membranes require a slightly larger pore diameter (7 A) than rigid membranes.
2016
Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W.; Poole, Peter H.
Potential energy landscape of the apparent first-order phase transition between low-density and high-density amorphous ice Journal Article
In: The Journal of Chemical Physics, vol. 145, no. 22, pp. 224501, 2016.
BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{gssp16,
title = {Potential energy landscape of the apparent first-order phase transition between low-density and high-density amorphous ice},
author = {Giovambattista, Nicolas and Sciortino, Francesco and Starr, Francis W. and Poole, Peter H.},
url = {http://fstarr.web.wesleyan.edu/publications/gssp16.pdf},
doi = {http://dx.doi.org/10.1063/1.4968047},
year = {2016},
date = {2016-01-01},
journal = {The Journal of Chemical Physics},
volume = {145},
number = {22},
pages = {224501},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
2014
Starr, Francis W.
PHYSICS OF WATER Crystal-clear transition Journal Article
In: NATURE PHYSICS, vol. 10, no. 9, pp. 628-629, 2014, ISSN: 1745-2473.
BibTeX | Tags: Polyamorphism, Water | Links:
@article{snv14,
title = {PHYSICS OF WATER Crystal-clear transition},
author = {Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/snv14.pdf},
doi = {10.1038/nphys3059},
issn = {1745-2473},
year = {2014},
date = {2014-09-01},
journal = {NATURE PHYSICS},
volume = {10},
number = {9},
pages = {628-629},
keywords = {Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas
Heating-induced glass-glass and glass-liquid transformations in computer simulations of water Journal Article
In: JOURNAL OF CHEMICAL PHYSICS, vol. 140, no. 11, pp. 114504, 2014, ISSN: 0021-9606.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{csg14,
title = {Heating-induced glass-glass and glass-liquid transformations in computer simulations of water},
author = {Chiu, Janet and Starr, Francis W. and Giovambattista, Nicolas},
url = {http://fstarr.web.wesleyan.edu/publications/csg14.pdf},
doi = {10.1063/1.4868028},
issn = {0021-9606},
year = {2014},
date = {2014-03-01},
journal = {JOURNAL OF CHEMICAL PHYSICS},
volume = {140},
number = {11},
pages = {114504},
abstract = {Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to- HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T ``phase diagram'' for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [ Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA). (C) 2014 AIP Publishing LLC.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to- HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T ``phase diagram'' for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [ Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA). (C) 2014 AIP Publishing LLC.
2013
Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas
Pressure-induced transformations in computer simulations of glassy water Journal Article
In: JOURNAL OF CHEMICAL PHYSICS, vol. 139, no. 18, pp. 184504, 2013, ISSN: 0021-9606.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{csg13,
title = {Pressure-induced transformations in computer simulations of glassy water},
author = {Chiu, Janet and Starr, Francis W. and Giovambattista, Nicolas},
url = {http://fstarr.web.wesleyan.edu/publications/csg13.pdf},
doi = {10.1063/1.4829276},
issn = {0021-9606},
year = {2013},
date = {2013-11-01},
journal = {JOURNAL OF CHEMICAL PHYSICS},
volume = {139},
number = {18},
pages = {184504},
abstract = {Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a ``P-T phase diagram'' for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water. (C) 2013 AIP Publishing LLC.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a ``P-T phase diagram'' for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water. (C) 2013 AIP Publishing LLC.
2012
Giovambattista, Nicolas; Loerting, Thomas; Lukanov, Boris R.; Starr, Francis W.
Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water Journal Article
In: SCIENTIFIC REPORTS, vol. 2, pp. 390, 2012, ISSN: 2045-2322.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{glls12,
title = {Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water},
author = {Giovambattista, Nicolas and Loerting, Thomas and Lukanov, Boris R. and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/glls12.pdf},
doi = {10.1038/srep00390},
issn = {2045-2322},
year = {2012},
date = {2012-05-01},
journal = {SCIENTIFIC REPORTS},
volume = {2},
pages = {390},
abstract = {Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature T-g. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of T-g(P) for LDA and HDA by performing computer simulations of two water models - one with a LLPT, and one without. In the absence of a LLPT, T-g(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different T-g(P) which are directly linked with the LLPT. Available experimental data for T-g(P) are only consistent with the scenario including a LLPT.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature T-g. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of T-g(P) for LDA and HDA by performing computer simulations of two water models - one with a LLPT, and one without. In the absence of a LLPT, T-g(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different T-g(P) which are directly linked with the LLPT. Available experimental data for T-g(P) are only consistent with the scenario including a LLPT.
2011
Poole, Peter H.; Becker, Stephen R.; Sciortino, Francesco; Starr, Francis W.
Dynamical Behavior Near a Liquid-Liquid Phase Transition in Simulations of Supercooled Water Journal Article
In: JOURNAL OF PHYSICAL CHEMISTRY B, vol. 115, no. 48, pp. 14176-14183, 2011, ISSN: 1520-6106.
Abstract | BibTeX | Tags: Polyamorphism, Water | Links:
@article{pbss11,
title = {Dynamical Behavior Near a Liquid-Liquid Phase Transition in Simulations of Supercooled Water},
author = {Poole, Peter H. and Becker, Stephen R. and Sciortino, Francesco and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/pbss11.pdf},
doi = {10.1021/jp204889m},
issn = {1520-6106},
year = {2011},
date = {2011-12-01},
journal = {JOURNAL OF PHYSICAL CHEMISTRY B},
volume = {115},
number = {48},
pages = {14176-14183},
abstract = {We examine the behavior of the diffusion coefficient of the ST2 model of water over a broad region of the phase diagram via molecular dynamics simulations. The ST2 model has an accessible liquid-liquid transition between low-density and high-density phases, making the model an ideal candidate to explore the impacts of the liquid-liquid transition on dynamics. We locate characteristic dynamical loci in the phase diagram and compare them with the previously investigated thermodynamic loci. The low-density liquid phase shows a crossover from non-Arrhenius to Arrhenius behavior, signaling the onset of a crossover from fragile-to-strong behavior. We explain this crossover in terms of the asymptotic approach of the low-density liquid to a random tetrahedral network and show that the temperature dependence of the diffusion coefficient over a wide temperature range can be simply related to the concentration of defects in the network. Our findings thus confirm that the low-density phase of ST2 water is a well-defined metastable liquid.},
keywords = {Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
We examine the behavior of the diffusion coefficient of the ST2 model of water over a broad region of the phase diagram via molecular dynamics simulations. The ST2 model has an accessible liquid-liquid transition between low-density and high-density phases, making the model an ideal candidate to explore the impacts of the liquid-liquid transition on dynamics. We locate characteristic dynamical loci in the phase diagram and compare them with the previously investigated thermodynamic loci. The low-density liquid phase shows a crossover from non-Arrhenius to Arrhenius behavior, signaling the onset of a crossover from fragile-to-strong behavior. We explain this crossover in terms of the asymptotic approach of the low-density liquid to a random tetrahedral network and show that the temperature dependence of the diffusion coefficient over a wide temperature range can be simply related to the concentration of defects in the network. Our findings thus confirm that the low-density phase of ST2 water is a well-defined metastable liquid.
2010
Rivera, Jose L.; Starr, Francis W.
Rapid Transport of Water via a Carbon Nanotube Syringe Journal Article
In: JOURNAL OF PHYSICAL CHEMISTRY C, vol. 114, no. 9, pp. 3737-3742, 2010, ISSN: 1932-7447.
Abstract | BibTeX | Tags: Nanotechnology, Water | Links:
@article{rs10,
title = {Rapid Transport of Water via a Carbon Nanotube Syringe},
author = {Rivera, Jose L. and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/rs10.pdf},
doi = {10.1021/jp906527c},
issn = {1932-7447},
year = {2010},
date = {2010-03-01},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
volume = {114},
number = {9},
pages = {3737-3742},
abstract = {The controlled flow of water molecules at the nanoscale is an initial step to many fluidic processes ill nanotechnology. Here we show how thin films of water call be drawn through a nanosyringe built from a carbon nanotube membrane and a ``plunger''. By increasing the speed of withdrawal of the plunger, we call obtain Molecular transport through the membrane at flux rates exceeding 1()25 molecules cm(-2) s(-1). Above I threshold speed around 0.25 nm/ns (25 cm/s), molecules cannot fill the chamber created by the plunger motion as fast as the chamber expands, and the resulting flux rate drops. By considering hydrophobic or hydrophilic Plungers, we unexpectedly find that the nature of the water-plunger interactions does not affect the flux rate or the threshold plunger speed. While the water structure near the plunger Surface differs significantly For different plunger interactions, the failure of the film away From the plunger surface is responsible for loss of transport. As I result, the surface interactions play a limited role in controlling the flux.},
keywords = {Nanotechnology, Water},
pubstate = {published},
tppubtype = {article}
}
The controlled flow of water molecules at the nanoscale is an initial step to many fluidic processes ill nanotechnology. Here we show how thin films of water call be drawn through a nanosyringe built from a carbon nanotube membrane and a ``plunger''. By increasing the speed of withdrawal of the plunger, we call obtain Molecular transport through the membrane at flux rates exceeding 1()25 molecules cm(-2) s(-1). Above I threshold speed around 0.25 nm/ns (25 cm/s), molecules cannot fill the chamber created by the plunger motion as fast as the chamber expands, and the resulting flux rate drops. By considering hydrophobic or hydrophilic Plungers, we unexpectedly find that the nature of the water-plunger interactions does not affect the flux rate or the threshold plunger speed. While the water structure near the plunger Surface differs significantly For different plunger interactions, the failure of the film away From the plunger surface is responsible for loss of transport. As I result, the surface interactions play a limited role in controlling the flux.
2009
Xu, Limei; Mallamace, Francesco; Yan, Zhenyu; Starr, Francis W.; Buldyrev, Sergey V.; Stanley, H. Eugene
Appearance of a fractional Stokes-Einstein relation in water and a structural interpretation of its onset Journal Article
In: NATURE PHYSICS, vol. 5, no. 8, pp. 565-569, 2009, ISSN: 1745-2473.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{xmysbs,
title = {Appearance of a fractional Stokes-Einstein relation in water and a structural interpretation of its onset},
author = {Xu, Limei and Mallamace, Francesco and Yan, Zhenyu and Starr, Francis W. and Buldyrev, Sergey V. and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/xmysbs.pdf},
doi = {10.1038/NPHYS1328},
issn = {1745-2473},
year = {2009},
date = {2009-08-01},
journal = {NATURE PHYSICS},
volume = {5},
number = {8},
pages = {565-569},
abstract = {The Stokes-Einstein relation has long been regarded as one of the hallmarks of transport in liquids. It predicts that the self-diffusion constant D is proportional to (tau/T)(-1), where tau is the structural relaxation time and T is the temperature. Here, we present experimental data on water confirming that, below a crossover temperature T-x approximate to 290 K, the Stokes-Einstein relation is replaced by a `fractional' Stokes-Einstein relation D similar to (tau/T)(-zeta) with zeta approximate to 3/5 (refs 1-6). We interpret the microscopic origin of this crossover by analysing the OH-stretch region of the Fourier transform infrared spectrum over a temperature range from 350 down to 200 K. Simultaneous with the onset of fractional Stokes-Einstein behaviour, we find that water begins to develop a local structure similar to that of low-density amorphous solid H2O. These data lead to an interpretation that the fractional Stokes-Einstein relation in water arises from a specific change in the local water structure. Computer simulations of two molecular models further support this interpretation.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
The Stokes-Einstein relation has long been regarded as one of the hallmarks of transport in liquids. It predicts that the self-diffusion constant D is proportional to (tau/T)(-1), where tau is the structural relaxation time and T is the temperature. Here, we present experimental data on water confirming that, below a crossover temperature T-x approximate to 290 K, the Stokes-Einstein relation is replaced by a `fractional' Stokes-Einstein relation D similar to (tau/T)(-zeta) with zeta approximate to 3/5 (refs 1-6). We interpret the microscopic origin of this crossover by analysing the OH-stretch region of the Fourier transform infrared spectrum over a temperature range from 350 down to 200 K. Simultaneous with the onset of fractional Stokes-Einstein behaviour, we find that water begins to develop a local structure similar to that of low-density amorphous solid H2O. These data lead to an interpretation that the fractional Stokes-Einstein relation in water arises from a specific change in the local water structure. Computer simulations of two molecular models further support this interpretation.
2008
Hsu, Chia Wei; Largo, Julio; Sciortino, Francesco; Starr, Francis W.
Hierarchies of networked phases induced by multiple liquid-liquid critical points Journal Article
In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, vol. 105, no. 37, pp. 13711-13715, 2008, ISSN: 0027-8424.
Abstract | BibTeX | Tags: Biophysics, DNA, Polyamorphism, Self Assembly, Water | Links:
@article{hlss08,
title = {Hierarchies of networked phases induced by multiple liquid-liquid critical points},
author = {Hsu, Chia Wei and Largo, Julio and Sciortino, Francesco and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/hlss.pdf},
doi = {10.1073/pnas.0804854105},
issn = {0027-8424},
year = {2008},
date = {2008-09-01},
journal = {PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA},
volume = {105},
number = {37},
pages = {13711-13715},
abstract = {Nanoparticles and colloids functionalized by four single strands of DNA can be thought of as designed analogs to tetrahedral network-forming atoms and molecules, with a difference that the attached DNA strands allow for control of the length scale of bonding relative to the core size. We explore the behavior of an experimentally realized model for nanoparticles functionalized by four single strands of DNA (a tetramer), and show that this single-component model exhibits a rich phase diagram with at least three critical points and four thermodynamically distinct amorphous phases. We demonstrate that the additional critical points are part of the Ising universality class, like the ordinary liquid-gas critical point. The dense phases consist of a hierarchy of interpenetrating networks, reminiscent of a woven cloth. Thus, bonding specificity of DNA provides an effective route to generate new nano-networked materials with polyamorphic behavior. The concept of network interpenetration helps to explain the generation of multiple liquid phases in sing le-component systems, suggested to occur in some atomic and molecular network-forming fluids, including water and silica.},
keywords = {Biophysics, DNA, Polyamorphism, Self Assembly, Water},
pubstate = {published},
tppubtype = {article}
}
Nanoparticles and colloids functionalized by four single strands of DNA can be thought of as designed analogs to tetrahedral network-forming atoms and molecules, with a difference that the attached DNA strands allow for control of the length scale of bonding relative to the core size. We explore the behavior of an experimentally realized model for nanoparticles functionalized by four single strands of DNA (a tetramer), and show that this single-component model exhibits a rich phase diagram with at least three critical points and four thermodynamically distinct amorphous phases. We demonstrate that the additional critical points are part of the Ising universality class, like the ordinary liquid-gas critical point. The dense phases consist of a hierarchy of interpenetrating networks, reminiscent of a woven cloth. Thus, bonding specificity of DNA provides an effective route to generate new nano-networked materials with polyamorphic behavior. The concept of network interpenetration helps to explain the generation of multiple liquid phases in sing le-component systems, suggested to occur in some atomic and molecular network-forming fluids, including water and silica.
2007
Rivera, Jose L.; Rico, Jose L.; Starr, Francis W.
Interaction of water with cap-ended defective and nondefective small carbon nanotubes Journal Article
In: JOURNAL OF PHYSICAL CHEMISTRY C, vol. 111, no. 51, pp. 18899-18905, 2007, ISSN: 1932-7447.
Abstract | BibTeX | Tags: Nanotechnology, Water | Links:
@article{rrs07,
title = {Interaction of water with cap-ended defective and nondefective small carbon nanotubes},
author = {Rivera, Jose L. and Rico, Jose L. and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/rrs.pdf},
doi = {10.1021/jp075989r},
issn = {1932-7447},
year = {2007},
date = {2007-12-01},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
volume = {111},
number = {51},
pages = {18899-18905},
abstract = {We present a theoretical study of the structure, local curvature angles, and reactivity of cap-ended (7,0), defective and nondefective carbon nanotubes. We find that the most reactive sites are the atoms that form part of the caps even when the Stone-Wales defect is present. Each carbon in the carbon nanotube is located at the top of a pyramidal structure with three walls of 5-, 6-, or 7-carbon rings. Among the carbons making up the caps, the most reactive sites are the top pyramidal atoms between two 5-carbon rings and one 6-carbon ring and each 5-carbon ring has attached another 5-carbon ring. The least reactive sites are the top pyramidal atoms between three 6-carbon rings. The. activity of each pyramidal structure is strongly correlated to its local curvature angle. The dissociation of one water molecule on the surface of the carbon nanotubes confirms the location of the most active site. The dissociation of water produces a hydroxyl group and a hydrogen atom united each to two adjacent carbon atoms. The dissociation process of water on carbon nanotubes is energetically favorable starting from the isolated molecules.},
keywords = {Nanotechnology, Water},
pubstate = {published},
tppubtype = {article}
}
We present a theoretical study of the structure, local curvature angles, and reactivity of cap-ended (7,0), defective and nondefective carbon nanotubes. We find that the most reactive sites are the atoms that form part of the caps even when the Stone-Wales defect is present. Each carbon in the carbon nanotube is located at the top of a pyramidal structure with three walls of 5-, 6-, or 7-carbon rings. Among the carbons making up the caps, the most reactive sites are the top pyramidal atoms between two 5-carbon rings and one 6-carbon ring and each 5-carbon ring has attached another 5-carbon ring. The least reactive sites are the top pyramidal atoms between three 6-carbon rings. The. activity of each pyramidal structure is strongly correlated to its local curvature angle. The dissociation of one water molecule on the surface of the carbon nanotubes confirms the location of the most active site. The dissociation of water produces a hydroxyl group and a hydrogen atom united each to two adjacent carbon atoms. The dissociation process of water on carbon nanotubes is energetically favorable starting from the isolated molecules.
Mazza, Marco G.; Giovambattista, Nicolas; Stanley, H. Eugene; Starr, Francis W.
Connection of translational and rotational dynamical heterogeneities with the breakdown of the Stokes-Einstein and Stokes-Einstein-Debye relations in water Journal Article
In: PHYSICAL REVIEW E, vol. 76, no. 3, pp. 031203, 2007, ISSN: 1539-3755.
Abstract | BibTeX | Tags: Dynamic Heterogeneity, Glass Formation, Water | Links:
@article{mgss-pre07,
title = {Connection of translational and rotational dynamical heterogeneities with the breakdown of the Stokes-Einstein and Stokes-Einstein-Debye relations in water},
author = {Mazza, Marco G. and Giovambattista, Nicolas and Stanley, H. Eugene and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/mgss-pre07.pdf},
doi = {10.1103/PhysRevE.76.031203},
issn = {1539-3755},
year = {2007},
date = {2007-09-01},
journal = {PHYSICAL REVIEW E},
volume = {76},
number = {3},
pages = {031203},
abstract = {We study the Stokes-Einstein (SE) and the Stokes-Einstein-Debye (SED) relations, D(t)=k(B)T/6 pi eta R and D(r)=k(B)T/8 pi eta R(3), where D(t) and D(r) are the translational and rotational diffusivity, respectively, T is the temperature, eta the viscosity, k(B) the Boltzmann constant, and R the ``molecular'' radius. Our results are based on molecular dynamics simulations of the extended simple point charge model of water. We find that both the SE and SED relations break down at low temperature. To explore the relationship between these breakdowns and dynamical heterogeneities (DHs), we also calculate the SE and SED relations for subsets of the 7% ``fastest'' and 7% ``slowest'' molecules. We find that the SE and SED relations break down in both subsets, and that the breakdowns occur on all scales of mobility. Thus these breakdowns appear to be generalized phenomena, in contrast with a view where only the most mobile molecules are the origin of the breakdown of the SE and SED relations, embedded in an inactive background where these relations hold. At low temperature, the SE and SED relations in both subsets of molecules are replaced with ``fractional'' SE and SED relations, D(t)similar to(tau/T)(-xi)(t) and D(r)similar to(tau/T)(-xi)(r), where xi(t)approximate to 0.84(< 1) and xi(r)approximate to 0.75(< 1). We also find that there is a decoupling between rotational and translational motion, and that this decoupling occurs in both the fastest and slowest subsets of molecules. Further, we find that, the decoupling increases upon cooling, but that the probability of a molecule being classified as both translationally and rotationally fastest also increases. To study the effect of time scale for SE and SED breakdown and decoupling, we introduce a time-dependent version of the SE and SED relations, and a time-dependent function that measures the extent of decoupling. Our results suggest that both the decoupling and SE and SED breakdowns originate at a time scale corresponding to the end of the cage regime, when diffusion starts. This is also the time scale when the DHs are more relevant. Our work also demonstrates that selecting DHs on the basis of translational or rotational motion more strongly biases the calculation of diffusion constants than other dynamical properties such as relaxation times.},
keywords = {Dynamic Heterogeneity, Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
We study the Stokes-Einstein (SE) and the Stokes-Einstein-Debye (SED) relations, D(t)=k(B)T/6 pi eta R and D(r)=k(B)T/8 pi eta R(3), where D(t) and D(r) are the translational and rotational diffusivity, respectively, T is the temperature, eta the viscosity, k(B) the Boltzmann constant, and R the ``molecular'' radius. Our results are based on molecular dynamics simulations of the extended simple point charge model of water. We find that both the SE and SED relations break down at low temperature. To explore the relationship between these breakdowns and dynamical heterogeneities (DHs), we also calculate the SE and SED relations for subsets of the 7% ``fastest'' and 7% ``slowest'' molecules. We find that the SE and SED relations break down in both subsets, and that the breakdowns occur on all scales of mobility. Thus these breakdowns appear to be generalized phenomena, in contrast with a view where only the most mobile molecules are the origin of the breakdown of the SE and SED relations, embedded in an inactive background where these relations hold. At low temperature, the SE and SED relations in both subsets of molecules are replaced with ``fractional'' SE and SED relations, D(t)similar to(tau/T)(-xi)(t) and D(r)similar to(tau/T)(-xi)(r), where xi(t)approximate to 0.84(< 1) and xi(r)approximate to 0.75(< 1). We also find that there is a decoupling between rotational and translational motion, and that this decoupling occurs in both the fastest and slowest subsets of molecules. Further, we find that, the decoupling increases upon cooling, but that the probability of a molecule being classified as both translationally and rotationally fastest also increases. To study the effect of time scale for SE and SED breakdown and decoupling, we introduce a time-dependent version of the SE and SED relations, and a time-dependent function that measures the extent of decoupling. Our results suggest that both the decoupling and SE and SED breakdowns originate at a time scale corresponding to the end of the cage regime, when diffusion starts. This is also the time scale when the DHs are more relevant. Our work also demonstrates that selecting DHs on the basis of translational or rotational motion more strongly biases the calculation of diffusion constants than other dynamical properties such as relaxation times.
Kumar, Pradeep; Buldyrev, Sergey V.; Becker, Stephen R.; Poole, Peter H.; Starr, Francis W.; Stanley, H. Eugene
Relation between the Widom line and the breakdown of the Stokes-Einstein relation in supercooled water Journal Article
In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, vol. 104, no. 23, pp. 9575-9579, 2007, ISSN: 0027-8424.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{kbbpss,
title = {Relation between the Widom line and the breakdown of the Stokes-Einstein relation in supercooled water},
author = {Kumar, Pradeep and Buldyrev, Sergey V. and Becker, Stephen R. and Poole, Peter H. and Starr, Francis W. and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/kbbpss.pdf},
doi = {10.1073/pnas.0702608104},
issn = {0027-8424},
year = {2007},
date = {2007-06-01},
journal = {PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA},
volume = {104},
number = {23},
pages = {9575-9579},
abstract = {Supercooled water exhibits a breakdown of the Stokes-Einstein relation between the diffusion constant D and the alpha relaxation time $tau(alpha)$. For water simulated with two different potentials, TIP5P and ST2, we find that the temperature of the decoupling of diffusion and alpha relaxation correlates with the temperature of the maximum in specific heat that corresponds to crossing the Widom line T(W)(P). Specifically, we find that our results for D tau(alpha)/T collapse onto a single ``master curve'' if temperature is replaced by T - T(W)(P). We further find that the size of the mobile molecule clusters (dynamical heterogeneities) increases sharply near T(W)w(P). Moreover, our calculations of mobile particle cluster size < n(t*)>(w) for different pressures, where t* is the time for which the mobile particle cluster size is largest, also collapse onto a single master curve if T is, replaced by T - T(W)(P). The crossover to a more locally structured low density liquid (LDL) as T -> T(W)(P) appears to be well correlated both with the breakdown of the Stokes-Einstein relation and with the growth of dynamic heterogeneities. Our results are consistent with the possibility that the breakdown of the SE relation in supercooled water at low pressures is associated with the hypothesized liquid-liquid phase transition.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
Supercooled water exhibits a breakdown of the Stokes-Einstein relation between the diffusion constant D and the alpha relaxation time $tau(alpha)$. For water simulated with two different potentials, TIP5P and ST2, we find that the temperature of the decoupling of diffusion and alpha relaxation correlates with the temperature of the maximum in specific heat that corresponds to crossing the Widom line T(W)(P). Specifically, we find that our results for D tau(alpha)/T collapse onto a single ``master curve'' if temperature is replaced by T - T(W)(P). We further find that the size of the mobile molecule clusters (dynamical heterogeneities) increases sharply near T(W)w(P). Moreover, our calculations of mobile particle cluster size < n(t*)>(w) for different pressures, where t* is the time for which the mobile particle cluster size is largest, also collapse onto a single master curve if T is, replaced by T - T(W)(P). The crossover to a more locally structured low density liquid (LDL) as T -> T(W)(P) appears to be well correlated both with the breakdown of the Stokes-Einstein relation and with the growth of dynamic heterogeneities. Our results are consistent with the possibility that the breakdown of the SE relation in supercooled water at low pressures is associated with the hypothesized liquid-liquid phase transition.
Kumar, Pradeep; Starr, Francis W.; Buldyrev, Sergey V.; Stanley, H. Eugene
Effect of water-wall interaction potential on the properties of nanoconfined water Journal Article
In: PHYSICAL REVIEW E, vol. 75, no. 1, 1, pp. 011202, 2007, ISSN: 1539-3755.
Abstract | BibTeX | Tags: Nanotechnology, Water | Links:
@article{ksbs,
title = {Effect of water-wall interaction potential on the properties of nanoconfined water},
author = {Kumar, Pradeep and Starr, Francis W. and Buldyrev, Sergey V. and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/ksbs.pdf},
doi = {10.1103/PhysRevE.75.011202},
issn = {1539-3755},
year = {2007},
date = {2007-01-01},
journal = {PHYSICAL REVIEW E},
volume = {75},
number = {1, 1},
pages = {011202},
abstract = {Much of the understanding of bulk liquids has progressed through study of the limiting case in which molecules interact via purely repulsive forces, such as a hard-core or ``repulsive ramp'' potential. In the same spirit, we report progress on the understanding of confined water by examining the behavior of waterlike molecules interacting with planar walls via purely repulsive forces and compare our results with those obtained for Lennard-Jones (LJ) interactions between the molecules and the walls. Specifically, we perform molecular dynamics simulations of 512 waterlike molecules interacting via the TIP5P potential and confined between two smooth planar walls that are separated by 1.1 nm. At this separation, there are either two or three molecular layers of water, depending on density. We study two different forms of repulsive confinement, when the water-wall interaction potential is either (i) 1/r(9) or (ii) a WCA-like repulsive potential. We find that the thermodynamic, dynamic, and structural properties of the liquid in purely repulsive confinements qualitatively match those for a system with a pure LJ attraction to the wall. In previous studies that include attractions, freezing into monolayer or trilayer ice was seen for this wall separation. Using the same separation as these previous studies, we find that the crystal state is not stable with 1/r(9) repulsive walls but is stable with WCA-like repulsive confinement. However, by carefully adjusting the separation of the plates with 1/r(9) repulsive interactions so that the effective space available to the molecules is the same as that for LJ confinement, we find that the same crystal phases are stable. This result emphasizes the importance of comparing systems only using the same effective confinement, which may differ from the geometric separation of the confining surfaces.},
keywords = {Nanotechnology, Water},
pubstate = {published},
tppubtype = {article}
}
Much of the understanding of bulk liquids has progressed through study of the limiting case in which molecules interact via purely repulsive forces, such as a hard-core or ``repulsive ramp'' potential. In the same spirit, we report progress on the understanding of confined water by examining the behavior of waterlike molecules interacting with planar walls via purely repulsive forces and compare our results with those obtained for Lennard-Jones (LJ) interactions between the molecules and the walls. Specifically, we perform molecular dynamics simulations of 512 waterlike molecules interacting via the TIP5P potential and confined between two smooth planar walls that are separated by 1.1 nm. At this separation, there are either two or three molecular layers of water, depending on density. We study two different forms of repulsive confinement, when the water-wall interaction potential is either (i) 1/r(9) or (ii) a WCA-like repulsive potential. We find that the thermodynamic, dynamic, and structural properties of the liquid in purely repulsive confinements qualitatively match those for a system with a pure LJ attraction to the wall. In previous studies that include attractions, freezing into monolayer or trilayer ice was seen for this wall separation. Using the same separation as these previous studies, we find that the crystal state is not stable with 1/r(9) repulsive walls but is stable with WCA-like repulsive confinement. However, by carefully adjusting the separation of the plates with 1/r(9) repulsive interactions so that the effective space available to the molecules is the same as that for LJ confinement, we find that the same crystal phases are stable. This result emphasizes the importance of comparing systems only using the same effective confinement, which may differ from the geometric separation of the confining surfaces.
2006
Rivera, Jose L.; Starr, Francis W.; Paricaud, Patrice; Cummings, Peter T.
Polarizable contributions to the surface tension of liquid water Journal Article
In: JOURNAL OF CHEMICAL PHYSICS, vol. 125, no. 9, pp. 094712, 2006, ISSN: 0021-9606.
Abstract | BibTeX | Tags: Water | Links:
@article{rspc,
title = {Polarizable contributions to the surface tension of liquid water},
author = {Rivera, Jose L. and Starr, Francis W. and Paricaud, Patrice and Cummings, Peter T.},
url = {http://fstarr.web.wesleyan.edu/publications/rspc.pdf},
doi = {10.1063/1.2345063},
issn = {0021-9606},
year = {2006},
date = {2006-09-01},
journal = {JOURNAL OF CHEMICAL PHYSICS},
volume = {125},
number = {9},
pages = {094712},
abstract = {Surface tension, gamma, strongly affects interfacial properties in fluids. The degree to which polarizability affects gamma in water is thus far not well established. To address this situation, we carry out molecular dynamics simulations to study the interfacial forces acting on a slab of liquid water surrounded by vacuum using the Gaussian charge polarizable (GCP) model at 298.15 K. The GCP model incorporates both a fixed dipole due to Gaussian distributed charges and a polarizable dipole. We find a well-defined bulklike region forms with a width of approximate to 31 A. The average density of the bulklike region agrees with the experimental value of 0.997 g/cm(3). However, we find that the orientation of the molecules in the bulklike region is strongly influenced by the interfaces, even at a distance five molecular diameters from the interface. Specifically, the orientations of both the permanent and induced dipoles show a preferred orientation parallel to the interface. Near the interface, the preferred orientation of the dipoles becomes more pronounced and the average magnitude of the induced dipoles decreases monotonically. To quantify the degree to which molecular orientation affects gamma, we calculate the contributions to gamma from permanent dipolar interactions, induced dipolar interactions, and dispersion forces. We find that the induced dipole interactions and the permanent dipole interactions, as well as the cross interactions, have positive contributions to gamma, and therefore contribute stability to the interface. The repulsive core interactions result in a negative contribution to gamma, which nearly cancels the positive contributions from the dipoles. The large negative core contributions to gamma are the result of small oxygen-oxygen separation between molecules. These small separations occur due to the strong attractions between hydrogen and oxygen atoms. The final predicted value for gamma (68.65 mN/m) shows a deviation of approximate to 4% of the experimental value of 71.972 mN/m. The inclusion of polarization is critical for this model to produce an accurate value. (c) 2006 American Institute of Physics.},
keywords = {Water},
pubstate = {published},
tppubtype = {article}
}
Surface tension, gamma, strongly affects interfacial properties in fluids. The degree to which polarizability affects gamma in water is thus far not well established. To address this situation, we carry out molecular dynamics simulations to study the interfacial forces acting on a slab of liquid water surrounded by vacuum using the Gaussian charge polarizable (GCP) model at 298.15 K. The GCP model incorporates both a fixed dipole due to Gaussian distributed charges and a polarizable dipole. We find a well-defined bulklike region forms with a width of approximate to 31 A. The average density of the bulklike region agrees with the experimental value of 0.997 g/cm(3). However, we find that the orientation of the molecules in the bulklike region is strongly influenced by the interfaces, even at a distance five molecular diameters from the interface. Specifically, the orientations of both the permanent and induced dipoles show a preferred orientation parallel to the interface. Near the interface, the preferred orientation of the dipoles becomes more pronounced and the average magnitude of the induced dipoles decreases monotonically. To quantify the degree to which molecular orientation affects gamma, we calculate the contributions to gamma from permanent dipolar interactions, induced dipolar interactions, and dispersion forces. We find that the induced dipole interactions and the permanent dipole interactions, as well as the cross interactions, have positive contributions to gamma, and therefore contribute stability to the interface. The repulsive core interactions result in a negative contribution to gamma, which nearly cancels the positive contributions from the dipoles. The large negative core contributions to gamma are the result of small oxygen-oxygen separation between molecules. These small separations occur due to the strong attractions between hydrogen and oxygen atoms. The final predicted value for gamma (68.65 mN/m) shows a deviation of approximate to 4% of the experimental value of 71.972 mN/m. The inclusion of polarization is critical for this model to produce an accurate value. (c) 2006 American Institute of Physics.
Becker, Stephen R.; Poole, Peter H.; Starr, Francis W.
Fractional Stokes-Einstein and Debye-Stokes-Einstein relations in a network-forming liquid Journal Article
In: PHYSICAL REVIEW LETTERS, vol. 97, no. 5, pp. 055901, 2006, ISSN: 0031-9007.
Abstract | BibTeX | Tags: Dynamic Heterogeneity, Glass Formation, Water | Links:
@article{bps06,
title = {Fractional Stokes-Einstein and Debye-Stokes-Einstein relations in a network-forming liquid},
author = {Becker, Stephen R. and Poole, Peter H. and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/bps.pdf},
doi = {10.1103/PhysRevLett.97.055901},
issn = {0031-9007},
year = {2006},
date = {2006-08-01},
journal = {PHYSICAL REVIEW LETTERS},
volume = {97},
number = {5},
pages = {055901},
abstract = {We study the breakdown of the Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) relations for translational and rotational motion in a prototypical model of a network-forming liquid, the ST2 model of water. We find that the emergence of fractional SE and DSE relations at low temperature is ubiquitous in this system, with exponents that vary little over a range of distinct physical regimes. We also show that the same fractional SE relation is obeyed by both mobile and immobile dynamical heterogeneities of the liquid.},
keywords = {Dynamic Heterogeneity, Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
We study the breakdown of the Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) relations for translational and rotational motion in a prototypical model of a network-forming liquid, the ST2 model of water. We find that the emergence of fractional SE and DSE relations at low temperature is ubiquitous in this system, with exponents that vary little over a range of distinct physical regimes. We also show that the same fractional SE relation is obeyed by both mobile and immobile dynamical heterogeneities of the liquid.
Mazza, MG; Giovambattista, Nicolas; Starr, Francis W.; Stanley, H. Eugene
Relation between rotational and translational dynamic heterogeneities in water Journal Article
In: PHYSICAL REVIEW LETTERS, vol. 96, no. 5, pp. 057803, 2006, ISSN: 0031-9007.
Abstract | BibTeX | Tags: Dynamic Heterogeneity, Glass Formation, Water | Links:
@article{mgss06,
title = {Relation between rotational and translational dynamic heterogeneities in water},
author = {Mazza, MG and Giovambattista, Nicolas and Starr, Francis W. and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/mgss.pdf},
doi = {10.1103/PhysRevLett.96.057803},
issn = {0031-9007},
year = {2006},
date = {2006-02-01},
journal = {PHYSICAL REVIEW LETTERS},
volume = {96},
number = {5},
pages = {057803},
abstract = {We use molecular dynamics simulations to probe the rotational dynamics of the extended simple point charge model of water for a range of temperatures down to 200 K, 6 K above the mode coupling temperature. We find that rotational dynamics is spatially heterogeneous; i.e., there are clusters of molecules that rotate significantly more than the average for a given time interval, and we study the size and the temporal behavior of these clusters. We find that the position of a rotational heterogeneity is strongly correlated with the position of a translational heterogeneity, and that the fraction of molecules belonging to both kinds of heterogeneities increases with decreasing temperature. We further find that although the two types of heterogeneities are not identical, they are related to the same physical picture.},
keywords = {Dynamic Heterogeneity, Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
We use molecular dynamics simulations to probe the rotational dynamics of the extended simple point charge model of water for a range of temperatures down to 200 K, 6 K above the mode coupling temperature. We find that rotational dynamics is spatially heterogeneous; i.e., there are clusters of molecules that rotate significantly more than the average for a given time interval, and we study the size and the temporal behavior of these clusters. We find that the position of a rotational heterogeneity is strongly correlated with the position of a translational heterogeneity, and that the fraction of molecules belonging to both kinds of heterogeneities increases with decreasing temperature. We further find that although the two types of heterogeneities are not identical, they are related to the same physical picture.
2005
Giovambattista, Nicolas; Buldyrev, Sergey V.; Stanley, H. Eugene; Starr, Francis W.
Clusters of mobile molecules in supercooled water Journal Article
In: PHYSICAL REVIEW E, vol. 72, no. 1, 1, pp. 011202, 2005, ISSN: 1539-3755.
Abstract | BibTeX | Tags: Dynamic Heterogeneity, Glass Formation, Water | Links:
@article{gbss05,
title = {Clusters of mobile molecules in supercooled water},
author = {Giovambattista, Nicolas and Buldyrev, Sergey V. and Stanley, H. Eugene and Starr, Francis W.},
url = {http://fstarr.web.wesleyan.edu/publications/gbss-pre05.pdf},
doi = {10.1103/PhysRevE.72.011202},
issn = {1539-3755},
year = {2005},
date = {2005-07-01},
journal = {PHYSICAL REVIEW E},
volume = {72},
number = {1, 1},
pages = {011202},
abstract = {We study the spatially heterogeneous dynamics in water via molecular dynamics simulations using the extended simple point charge potential. We identify clusters formed by mobile molecules and study their properties. We find that these clusters grow in size and become more compact as temperature decreases. We analyze the probability density function of cluster size, and we study the cluster correlation length. We find that clusters appear to be characterized by a fractal dimension consistent with that of lattice animals. We relate the cluster size and correlation length to the configurational entropy, S-conf. We find that these quantities depend weakly on 1/S-conf. In particular, the linearity found between the cluster mass n(*) and 1/S-conf suggests that n(*) may be interpreted as the mass of the cooperatively rearranging regions that form the basis of the Adam-Gibbs approach to the dynamics of supercooled liquids. We study the motion of molecules within a cluster, and find that each molecule preferentially follows a neighboring molecule in the same cluster. Based on this finding we hypothesize that stringlike cooperative motion may be a general mechanism for molecular rearrangement of complex, as well as simple liquids. By mapping each equilibrium configuration onto its corresponding local potential energy minimum or inherent structure (IS), we are able to compare the mobile molecule clusters in the equilibrium system with the molecules forming the clusters identified in the transitions between IS. We find that (i) mobile molecule clusters obtained by comparing different system configurations and (ii) clusters obtained by comparing the corresponding IS are completely different for short time scales, but are the same on the longer time scales of diffusive motion.},
keywords = {Dynamic Heterogeneity, Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
We study the spatially heterogeneous dynamics in water via molecular dynamics simulations using the extended simple point charge potential. We identify clusters formed by mobile molecules and study their properties. We find that these clusters grow in size and become more compact as temperature decreases. We analyze the probability density function of cluster size, and we study the cluster correlation length. We find that clusters appear to be characterized by a fractal dimension consistent with that of lattice animals. We relate the cluster size and correlation length to the configurational entropy, S-conf. We find that these quantities depend weakly on 1/S-conf. In particular, the linearity found between the cluster mass n(*) and 1/S-conf suggests that n(*) may be interpreted as the mass of the cooperatively rearranging regions that form the basis of the Adam-Gibbs approach to the dynamics of supercooled liquids. We study the motion of molecules within a cluster, and find that each molecule preferentially follows a neighboring molecule in the same cluster. Based on this finding we hypothesize that stringlike cooperative motion may be a general mechanism for molecular rearrangement of complex, as well as simple liquids. By mapping each equilibrium configuration onto its corresponding local potential energy minimum or inherent structure (IS), we are able to compare the mobile molecule clusters in the equilibrium system with the molecules forming the clusters identified in the transitions between IS. We find that (i) mobile molecule clusters obtained by comparing different system configurations and (ii) clusters obtained by comparing the corresponding IS are completely different for short time scales, but are the same on the longer time scales of diffusive motion.
2003
Starr, Francis W.; Angell, C. Austen; Stanley, H. Eugene
Prediction of entropy and dynamic properties of water below the homogeneous nucleation temperature Journal Article
In: PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, vol. 323, pp. 51-66, 2003, ISSN: 0378-4371.
Abstract | BibTeX | Tags: Glass Formation, Polyamorphism, Water | Links:
@article{sas03,
title = {Prediction of entropy and dynamic properties of water below the homogeneous nucleation temperature},
author = {Starr, Francis W. and Angell, C. Austen and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/sas.pdf},
doi = {10.1016/S0378-4371(03)00012-8},
issn = {0378-4371},
year = {2003},
date = {2003-05-01},
journal = {PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS},
volume = {323},
pages = {51-66},
abstract = {The behavior of thermodynamic and dynamic properties of liquid water at atmospheric pressure in the temperature range between the lower limit of supercooling (T-H approximate to 235 K) and the onset of the glassy state at T-g has been the focus of much research, and many questions remain about the properties of water in this region. Since direct measurements on water in this temperature range remain largely infeasible, we use existing experimental measurements of the entropy, specific heat, and enthalpy outside this range to construct a possible form of the entropy in the ``difficult-to-probe'' region. Assuming that the entropy is well-defined in extreme metastable states, and that there is no intervening discontinuity at atmospheric pressure, we estimate the excess entropy S-ex of the liquid over the crystal within relatively narrow limits. We find that our approximate form for S-ex shows atypical behavior when compared with other liquids: using a thermodynamic categorization of ``strong'' and ``fragile'' liquids, water appears to be fragile on initial cooling below the melting temperature, and strong in the temperature region near the glass transition. This thermodynamic construction can be used, with appropriate reservations, to estimate the behavior of the dynamic properties of water by means of the Adam-Gibbs equation-which relates configurational entropy S-conf to dynamic behavior. Although the Adam-Gibbs equation uses S-conf rather than S-ex as the control variable, the relation has been used successfully in a number of experimental studies with S-conf replaced by S-ex. This is likely a result of a proportionality between S-conf and S-ex, which we confirm for simulations of a model of water. Hence by using the constructed values of S-ex, together with experimental data in the range where S-ex is known, we estimate the temperature dependence of viscosity and diffusivity approaching the glass transition. Like the entropy plots, Arrhenius plots of viscosity or diffusion show an inflection, implying a crossover from fragile to strong liquid character below T-H. The dynamics results also imply T-g approximate to 160 K, which is considerably above the expected value of 136 K from older experiments, but consistent with other recent evidence based on hyperquenched glass properties. We discuss the possibility of experimentally verifying our predictions, and briefly discuss other liquids that also may follow a strong-to-fragile pattern. (C) 2003 Elsevier Science B.V. All rights reserved.},
keywords = {Glass Formation, Polyamorphism, Water},
pubstate = {published},
tppubtype = {article}
}
The behavior of thermodynamic and dynamic properties of liquid water at atmospheric pressure in the temperature range between the lower limit of supercooling (T-H approximate to 235 K) and the onset of the glassy state at T-g has been the focus of much research, and many questions remain about the properties of water in this region. Since direct measurements on water in this temperature range remain largely infeasible, we use existing experimental measurements of the entropy, specific heat, and enthalpy outside this range to construct a possible form of the entropy in the ``difficult-to-probe'' region. Assuming that the entropy is well-defined in extreme metastable states, and that there is no intervening discontinuity at atmospheric pressure, we estimate the excess entropy S-ex of the liquid over the crystal within relatively narrow limits. We find that our approximate form for S-ex shows atypical behavior when compared with other liquids: using a thermodynamic categorization of ``strong'' and ``fragile'' liquids, water appears to be fragile on initial cooling below the melting temperature, and strong in the temperature region near the glass transition. This thermodynamic construction can be used, with appropriate reservations, to estimate the behavior of the dynamic properties of water by means of the Adam-Gibbs equation-which relates configurational entropy S-conf to dynamic behavior. Although the Adam-Gibbs equation uses S-conf rather than S-ex as the control variable, the relation has been used successfully in a number of experimental studies with S-conf replaced by S-ex. This is likely a result of a proportionality between S-conf and S-ex, which we confirm for simulations of a model of water. Hence by using the constructed values of S-ex, together with experimental data in the range where S-ex is known, we estimate the temperature dependence of viscosity and diffusivity approaching the glass transition. Like the entropy plots, Arrhenius plots of viscosity or diffusion show an inflection, implying a crossover from fragile to strong liquid character below T-H. The dynamics results also imply T-g approximate to 160 K, which is considerably above the expected value of 136 K from older experiments, but consistent with other recent evidence based on hyperquenched glass properties. We discuss the possibility of experimentally verifying our predictions, and briefly discuss other liquids that also may follow a strong-to-fragile pattern. (C) 2003 Elsevier Science B.V. All rights reserved.
Giovambattista, Nicolas; Buldyrev, Sergey V.; Starr, Francis W.; Stanley, H. Eugene
Connection between Adam-Gibbs theory and spatially heterogeneous dynamics Journal Article
In: PHYSICAL REVIEW LETTERS, vol. 90, no. 8, pp. 085506, 2003, ISSN: 0031-9007.
Abstract | BibTeX | Tags: Dynamic Heterogeneity, Glass Formation, Water | Links:
@article{gbss03,
title = {Connection between Adam-Gibbs theory and spatially heterogeneous dynamics},
author = {Giovambattista, Nicolas and Buldyrev, Sergey V. and Starr, Francis W. and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/gbss.pdf},
doi = {10.1103/PhysRevLett.90.085506},
issn = {0031-9007},
year = {2003},
date = {2003-02-01},
journal = {PHYSICAL REVIEW LETTERS},
volume = {90},
number = {8},
pages = {085506},
abstract = {We investigate the spatially heterogeneous dynamics in the extended simple point charge model of water using molecular dynamics simulations. We relate the average mass n(*) of mobile particle clusters to the diffusion constant and the configurational entropy. Hence, n(*) can be interpreted as the mass of the ``cooperatively rearranging regions'' that form the basis of the Adam-Gibbs theory of the dynamics of supercooled liquids. We also examine the time and temperature dependence of these transient clusters.},
keywords = {Dynamic Heterogeneity, Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
We investigate the spatially heterogeneous dynamics in the extended simple point charge model of water using molecular dynamics simulations. We relate the average mass n(*) of mobile particle clusters to the diffusion constant and the configurational entropy. Hence, n(*) can be interpreted as the mass of the ``cooperatively rearranging regions'' that form the basis of the Adam-Gibbs theory of the dynamics of supercooled liquids. We also examine the time and temperature dependence of these transient clusters.
2000
Scala, Antonio; Starr, Francis W.; La Nave, Emilia; Sciortino, Francesco; Stanley, H. Eugene
Configurational entropy and diffusivity of supercooled water Journal Article
In: NATURE, vol. 406, no. 6792, pp. 166-169, 2000, ISSN: 0028-0836.
Abstract | BibTeX | Tags: Glass Formation, Water | Links:
@article{sslss-nature,
title = {Configurational entropy and diffusivity of supercooled water},
author = {Scala, Antonio and Starr, Francis W. and La Nave, Emilia and Sciortino, Francesco and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/sslss-nature.pdf},
issn = {0028-0836},
year = {2000},
date = {2000-07-01},
journal = {NATURE},
volume = {406},
number = {6792},
pages = {166-169},
abstract = {As a liquid approaches the glass transition, its properties are dominated by local potential minima(1,2) in its energy landscape. The liquid experiences localized vibrations in the basins of attraction surrounding the minima, and rearranges via relatively infrequent inter-basin jumps(3). As a result, the liquid dynamics at low temperature are related to the system's exploration of its own configuration space. The `thermodynamic approach' to the glass transition considers the reduction in configuration space(4-8) explored as the system cools, and predicts that the configurational entropy(5,9,10) (a measure of the number of local potential energy minima sampled by the liquid) is related to the diffusion constant. Here we report a stringent test of the thermodynamic approach for liquid water (a convenient system to study because of an anomalous pressure dependence in the diffusion constant). We calculate the configurational entropy at points spanning a large region of the temperature-density plane, using a model(11) that reproduces the dynamical anomalies of liquid water. We find that the thermodynamic approach can be used to understand the characteristic dynamic anomalies, and that the diffusive dynamics are governed by the configurational entropy. Our results indicate that the thermodynamic approach might be extended to predict the dynamical behaviour of supercooled liquids in general.},
keywords = {Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
As a liquid approaches the glass transition, its properties are dominated by local potential minima(1,2) in its energy landscape. The liquid experiences localized vibrations in the basins of attraction surrounding the minima, and rearranges via relatively infrequent inter-basin jumps(3). As a result, the liquid dynamics at low temperature are related to the system's exploration of its own configuration space. The `thermodynamic approach' to the glass transition considers the reduction in configuration space(4-8) explored as the system cools, and predicts that the configurational entropy(5,9,10) (a measure of the number of local potential energy minima sampled by the liquid) is related to the diffusion constant. Here we report a stringent test of the thermodynamic approach for liquid water (a convenient system to study because of an anomalous pressure dependence in the diffusion constant). We calculate the configurational entropy at points spanning a large region of the temperature-density plane, using a model(11) that reproduces the dynamical anomalies of liquid water. We find that the thermodynamic approach can be used to understand the characteristic dynamic anomalies, and that the diffusive dynamics are governed by the configurational entropy. Our results indicate that the thermodynamic approach might be extended to predict the dynamical behaviour of supercooled liquids in general.
1999
Starr, Francis W.; Sciortino, Francesco; Stanley, H. Eugene
Dynamics of simulated water under pressure Journal Article
In: PHYSICAL REVIEW E, vol. 60, no. 6, A, pp. 6757-6768, 1999, ISSN: 1063-651X.
Abstract | BibTeX | Tags: Glass Formation, Water | Links:
@article{sss99,
title = {Dynamics of simulated water under pressure},
author = {Starr, Francis W. and Sciortino, Francesco and Stanley, H. Eugene},
url = {http://fstarr.web.wesleyan.edu/publications/sss.pdf},
doi = {10.1103/PhysRevE.60.6757},
issn = {1063-651X},
year = {1999},
date = {1999-12-01},
journal = {PHYSICAL REVIEW E},
volume = {60},
number = {6, A},
pages = {6757-6768},
abstract = {We present molecular dynamics simulations of the extended simple-point-charge model of water to probe the dynamic properties at temperatures from 350 K down to 190 K and pressures from 2.5 GPa (25 kbar) down to -300 MPa (-3 kbar). We compare our results with those obtained experimentally, both of which show a diffusivity maximum as a function of pressure. We find that our simulation results are consistent with the predictions of the mode-coupling theory for the dynamics of weakly supercooled liquids-strongly supporting the hypothesis that the apparent divergences of dynamic properties observed experimentally may be independent of a possible thermodynamic singularity at low temperature. The dramatic change in water's dynamic and structural properties as a function of pressure allows us to confirm the predictions of MCT over a much broader range of the von Schweidler exponent values than has been studied for simple atomic liquids. We also show how structural changes are reflected in the wave-vector dependence of dynamic properties of the liquid along a path of nearly constant diffusivity. For temperatures below the crossover temperature of MCT (where the predictions of MCT are expected to fail), we find tentative evidence for a crossover of the temperature dependence of the diffusivity from power-law to Arrhenius behavior, with an activation energy typical of a strong liquid. [S1063-651X(99)11712-4].},
keywords = {Glass Formation, Water},
pubstate = {published},
tppubtype = {article}
}
We present molecular dynamics simulations of the extended simple-point-charge model of water to probe the dynamic properties at temperatures from 350 K down to 190 K and pressures from 2.5 GPa (25 kbar) down to -300 MPa (-3 kbar). We compare our results with those obtained experimentally, both of which show a diffusivity maximum as a function of pressure. We find that our simulation results are consistent with the predictions of the mode-coupling theory for the dynamics of weakly supercooled liquids-strongly supporting the hypothesis that the apparent divergences of dynamic properties observed experimentally may be independent of a possible thermodynamic singularity at low temperature. The dramatic change in water's dynamic and structural properties as a function of pressure allows us to confirm the predictions of MCT over a much broader range of the von Schweidler exponent values than has been studied for simple atomic liquids. We also show how structural changes are reflected in the wave-vector dependence of dynamic properties of the liquid along a path of nearly constant diffusivity. For temperatures below the crossover temperature of MCT (where the predictions of MCT are expected to fail), we find tentative evidence for a crossover of the temperature dependence of the diffusivity from power-law to Arrhenius behavior, with an activation energy typical of a strong liquid. [S1063-651X(99)11712-4].