Dynamical Screening and Ionic Conductivity in Water from<i>Ab Initio</i>Simulations

French, Martin; Hamel, Sébastien; Redmer, R.

doi:10.1103/physrevlett.107.185901

Cited by 48 publications

(59 citation statements)

References 34 publications

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“…Combining this formalism with a ground-state DFT-MD run enabled them to calculate the nuclear thermal conductivity for electronically insulating systems, which is adequate for liquid water. However, this elaborate procedure enhances the computing time of a DFT-MD simulation run by significant factor, similarly as occurs in analogous calculations of ionic conductivities [36,37].…”

Section: Resultsmentioning

confidence: 98%

Thermal conductivity of dissociating water—anab initiostudy

French

2019

New J. Phys.

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The thermal conductivity of partially dissociated and ionised water is calculated in a large-scale study using density functional theory (DFT)-based molecular dynamics (MD) simulations. In doing so, the required heat current of the nuclei is calculated by mapping the effective particle interactions from the DFT-MD simulations onto classical pair potentials. It is demonstrated that experimental and theoretical thermal conductivity data for liquid heavy water and for ice VII are well reproduced with this efficient procedure. Moreover, the approach also allows for an illustrative interpretation of the characteristics of the thermal conductivity in the dense chemically reacting fluid. The thermodynamic conditions investigated here range from densities between 0.2 and 6 g cm −3 and temperatures between 600 and 50000 K, which includes states highly relevant for understanding the interiors of water-rich planets like Uranus and Neptune and exoplanets of similar composition. During the last two decades, ab initio calculations based on finite-temperature density functional theory (FT-DFT) in combination with molecular dynamics (MD) simulations have become a reliable tool for accurate predictions of thermodynamic properties of matter under extreme conditions [12,13]. The prefix FT emphasises that the electron system is consistently treated at a nonzero (finite) temperature [14], which is typically equal to the temperature of the nuclei.The calculation of the thermal conductivity with FT-DFT-MD techniques requires a distincted treatment of the contributions from electronic heat conduction and from heat transport via the nuclei. The former is gained by evaluating the electronic Onsager coefficients using the Kohn-Sham eigenvalues and orbitals from the FT-DFT [15], which was recently accomplished also for partially ionised water [16].

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Section: Resultsmentioning

confidence: 98%

Thermal conductivity of dissociating water—anab initiostudy

French

2019

New J. Phys.

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“…Hence, their investigation calls for the use of quantum mechanical calculations, which are usually rather demanding from a computational standpoint. To this date there have been few ab initio simulations of high-pressure water encompassing structural, vibrational, and transport properties (e.g., ionic conduction); for example, no vibrational spectra have been computed for the fluid close to the ice VII melting line, and water conductivity has been investigated primarily at conditions well above 20 GPa (6)(7)(8)(9).…”

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confidence: 99%

“…In addition, three markedly different locations for the triple point of the liquid, ice VII, and ice X have been proposed in the literature (17), differing by 500 K and 10 GPa. The structural and dynamical properties of the fluid close to melting are also not well established, with ongoing debates on many fronts, including the existence of plastic ice phases close to the ice VII melting line (18,19), the molecular or dissociative nature of water (20), and the primary mechanism of ionic conduction (9,21). Some studies suggested a unimolecular dissociation process (7,(22)(23)(24)(25), H2O → H + + OH − occurring above 10 GPa and 1,000 K, while others pointed at the existence of bimolecular dissociation (8,12,26), i.e., 2H2O → H3O + + OH − similar to low pressure, with some experiments being unable to corroborate either mechanism (27).…”

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confidence: 99%

Ab initio spectroscopy and ionic conductivity of water under Earth mantle conditions

Rozsa

Pan

Giberti

et al. 2018

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

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The phase diagram of water at extreme conditions plays a critical role in Earth and planetary science, yet remains poorly understood. Here we report a first-principles investigation of the liquid at high temperature, between 11 GPa and 20 GPa-a region where numerous controversial results have been reported over the past three decades. Our results are consistent with the recent estimates of the water melting line below 1,000 K and show that on the 1,000-K isotherm the liquid is rapidly dissociating and recombining through a bimolecular mechanism. We found that short-lived ionic species act as charge carriers, giving rise to an ionic conductivity that at 11 GPa and 20 GPa is six and seven orders of magnitude larger, respectively, than at ambient conditions. Conductivity calculations were performed entirely from first principles, with no a priori assumptions on the nature of charge carriers. Despite frequent dissociative events, we observed that hydrogen bonding persists at high pressure, up to at least 20 GPa. Our computed Raman spectra, which are in excellent agreement with experiment, show no distinctive signatures of the hydronium and hydroxide ions present in our simulations. Instead, we found that infrared spectra are sensitive probes of molecular dissociation, exhibiting a broad band below the OH stretching mode ascribable to vibrations of complex ions.

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“…41 As shown in equation (1) and (2) , the electrical conductivity σ is given by a time integral over a current-current autocorrelation function:…”

Section: Electrical Conductivitymentioning

confidence: 99%

First-Principles Molecular Dynamics Study of a Hydrocarbon Copolymer for Use in Polymer Electrolyte Membrane Fuel Cells

et al. 2016

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The structural and dynamic properties of a brush-type hydrocarbon copolymer are investigated using first-principles molecular dynamics simulations. Two model compounds, one with mainly hydrophilic domains and one with mainly hydrophobic domains, were selected and used in the simulations. A series of radial distribution functions of different groups, such as water-water, sulfonic group-hydrogen, and etherhydrogen, is obtained to investigate the structure of the whole systems. The radial distribution functions of sulfonic groups, g S−S (r), and the structure of water clusters indicate the formation of a well-developed water channel in the studied copolymer.Analysis of proton dissociation reveals that the protons in both systems are not completely dissociated when the number of water molecules per sulfonic group is equal to 4. The low dissociation nature of this copolymer compared with that of Nafion is explained by its intrinsic acid strength and the presence of ineffective hydrogen bonds in the system, where ineffective hydrogen bonds indicate hydrogen bonds that do not contribute strongly to proton transport. The proton conductivity of this copolymer is comparable to that of Nafion, which is ascribed to the formation of good water channels. In addition, the calculated electrical conductivity of the two model compounds shows good agreement with the measured proton conductivity of this copolymer.

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Dynamical Screening and Ionic Conductivity in Water fromAb InitioSimulations

Cited by 48 publications

References 34 publications

Thermal conductivity of dissociating water—anab initiostudy

Thermal conductivity of dissociating water—anab initiostudy

Ab initio spectroscopy and ionic conductivity of water under Earth mantle conditions

First-Principles Molecular Dynamics Study of a Hydrocarbon Copolymer for Use in Polymer Electrolyte Membrane Fuel Cells

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