Low‐Density Equation of State for Water from a Chemical Model

Schöttler, Manuel; Redmer, R.; French, Martin

doi:10.1002/ctpp.201300020

Cited by 10 publications

(6 citation statements)

References 36 publications

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“…The formalism described above is now applied to various FT-DFT-MD simulations of warm dense water performed with the VASP code [26][27][28] and the PBE exchange correlation functional [29]. Most of the simulation parameters were set to values well-proven for calculating equation of state and diffusion coefficients [30][31][32][33]. The major modification here is the large extension in simulation time, so that now between 50000 and 250000 time steps (typical length of a time step: 0.3-0.5 fs) are simulated.…”

Section: Theoretical Methods and Simulation Proceduresmentioning

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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Section: Theoretical Methods and Simulation Proceduresmentioning

confidence: 99%

Thermal conductivity of dissociating water—anab initiostudy

French

2019

New J. Phys.

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“…With few modifications, i.e., leaving out the term containing ω 1 and setting k 0 = 3k max /2 and i 0 = i max , it is possible to achieve compatibility with both the Thomas-Fermi and the classical ideal gas limits. A combination with additional terms that describe EOS behavior at low densities [66], which is characterized by various thermal dissociation and ionization processes, seems achievable as well.…”

Section: A Main Contribution From the Ft-dft-mdmentioning

confidence: 99%

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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“…Achieving good numerical convergence of all physical quantities calculated with DFT-MD is of utmost importance and must be ensured [53]. Since we extensively applied the same DFT-MD simulation technique in previous work on water [54][55][56][57][58][59][60], we can rely, to a large extent, on the extensive numerical testing that was done there. For example, the validity of the standard PAW pseudopotentials for hydrogen and oxygen under the conditions of interest was shown [54].…”

Section: Fig 1 (Color Online) Idealizedmentioning

confidence: 99%

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

French

Redmer

2015

Phys. Rev. B

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We employ a combination of density functional theory (DFT), molecular dynamics (MD), and a variety of advanced postprocessing methods to construct an analytic thermodynamic potential (free energy) for ices VII and X. In particular, the temperature-dependent part of the free energy function is constructed using entropy data obtained via the spectrum of vibrational modes from the MD simulations. Conceptional challenges due to the partial absence of stable zero-temperature states and proton disorder are overcome by performing calculations of representative crystalline states combined with a three-stage fitting procedure of data from MD simulations and static DFT calculations. The influence of the exchange-correlation functional is extensively discussed, and a comparison with available experiments is made as well and generally shows good agreement. This work is of significant importance for astrophysical applications, such as the interior modeling of dense icy planets and moons.

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Low‐Density Equation of State for Water from a Chemical Model

Cited by 10 publications

References 36 publications

Thermal conductivity of dissociating water—anab initiostudy

Thermal conductivity of dissociating water—anab initiostudy

Ab initiocalculation of thermodynamic potentials and entropies for superionic water

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

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