Construction of a thermodynamic potential for the water ices VII and X

French, Martin; Redmer, R.

doi:10.1103/physrevb.91.014308

Cited by 43 publications

(69 citation statements)

References 83 publications

(131 reference statements)

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“…Quantum effects of the nuclear motion cannot be neglected when calculating the thermodynamic properties of SIW. Equation (3) allows us to include such effects at the same level as was recently done for the ices VII and X [30] or earlier calculations for fluid water [44,67]. In the case of fluid ammonia, it was shown that the method can capture effects of thermal dissociation that lead to an increased decay of the nuclear quantum effects due to the loss of intramolecular modes of vibration [61].…”

Section: B Nuclear Quantum Correctionmentioning

confidence: 99%

“…Having obtained the complete thermodynamic information of the SIW phases, we then investigate the location of transitions between them. The boundary to the dense ices VII and X, for which a corresponding thermodynamic potential is also available [30], is calculated as well. It is in good agreement with that observed directly in the MD simulations.…”

Section: Introductionmentioning

confidence: 99%

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Ab initiocalculation of thermodynamic potentials and entropies for superionic water

2016

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We construct thermodynamic potentials for two superionic phases of water [with body-centered cubic (bcc) and face-centered cubic (fcc) oxygen lattice] using a combination of density functional theory (DFT) and molecular dynamics simulations (MD). For this purpose, a generic expression for the free energy of warm dense matter is developed and parametrized with equation of state data from the DFT-MD simulations. A second central aspect is the accurate determination of the entropy, which is done using an approximate two-phase method based on the frequency spectra of the nuclear motion. The boundary between the bcc superionic phase and the ices VII and X calculated with thermodynamic potentials from DFT-MD is consistent with that directly derived from the simulations. Differences in the physical properties of the bcc and fcc superionic phases and their impact on interior modeling of water-rich giant planets are discussed.

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Section: B Nuclear Quantum Correctionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ab initiocalculation of thermodynamic potentials and entropies for superionic water

2016

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“…Lower: thermal conductivity of ice VII at T=300 K in comparison with experiments[39,40]. Pressures for the DFT-MD+GKFF points were calculated with an equation of state[41].…”

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confidence: 99%

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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“…This transition sequence-orientational disorder (ice VII) to dynamical disorder (ice VII 0 ) to ionic ice (ice X) -was studied at ambient temperature, but few studies mention it at high temperature [21,22]. With increasing temperatures, the mobility of the protons is enhanced such that H 2 O ice reaches a superionic state [23] while the sublattice of oxygen atoms remains fixed.…”

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Superionic-Superionic Phase Transitions in Body-Centered CubicH2OIce

Hernandez

Caracas

2016

Phys. Rev. Lett.

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From first-principles molecular dynamics, we investigate the relation between the superionic proton conduction and the behavior of the O─H⋯O bond (ice VII^{'} to ice X transition) in body-centered-cubic (bcc) H_{2}O ice between 1300 and 2000 K and up to 300 GPa. We bring evidence that there are three distinct phases in the superionic bcc stability field. A first superionic phase characterized by extremely fast diffusion of highly delocalized protons (denoted VII^{''} hereinafter) is stable at low pressures. A first-order transition separates this phase from a superionic VII^{'}, characterized by a finite degree of localization of protons along the nonsymmetric O─H⋯O bonds. The transition is identified in structural, energetic, and elastic analysis. Upon further compression a second-order phase transition leads to the superionic ice X with symmetric O─H─O bonds.

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Construction of a thermodynamic potential for the water ices VII and X

Cited by 43 publications

References 83 publications

Ab initiocalculation of thermodynamic potentials and entropies for superionic water

Ab initiocalculation of thermodynamic potentials and entropies for superionic water

Thermal conductivity of dissociating water—anab initiostudy

Superionic-Superionic Phase Transitions in Body-Centered CubicH2OIce

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