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Matthias Scheffler - One of the best experts on this subject based on the ideXlab platform.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
Journal of Chemical Physics, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [B. Santra, J. Klimes, D. Alfe, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
arXiv: Materials Science, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
G Tobie - One of the best experts on this subject based on the ideXlab platform.
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two phase convection in ganymede s high Pressure Ice layer implications for its geological evolution
Icarus, 2018Co-Authors: Klara Kalousova, G Tobie, C Sotin, Gael Choblet, O GrassetAbstract:Abstract Ganymede, the largest moon in the solar system, has a fully differentiated interior with a layer of high-Pressure (HP) Ice between its deep ocean and silicate mantle. In this paper, we study the dynamics of this layer using a numerical model of two-phase Ice–water mixture in two-dimensional Cartesian geometry. While focusing on the generation of water at the silicate/HP Ice interface and its upward migration towards the ocean, we investigate the effect of bottom heat flux, the layer thickness, and the HP Ice viscosity and permeability. Our results suggest that melt can be generated at the silicate/HP Ice interface for small layer thickness ( ≲ 200 km) and high values of heat flux ( ≳ 20 mW m − 2 ) and viscosity ( ≳ 1015 Pa s). Once generated, the water is transported through the layer by the upwelling plumes. Depending on the vigor of convection, it stays liquid or it may freeze before melting again as the plume reaches the temperate (partially molten) layer at the boundary with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the permeability of the HP Ice. This process constitutes a means of transporting volatiles and salts that might have dissolved into the melt present at the silicate/HP Ice interface. As the moon cools down, the HP Ice layer becomes less permeable because the heat flux from the silicates decreases and the HP Ice layer thickens.
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geophysical investigations of habitability in Ice covered ocean worlds
Journal of Geophysical Research, 2017Co-Authors: Steven D Vance, G Tobie, M P Panning, Simon C Stahler, Fabio Cammarano, B G Bills, Shunichi Kamata, Sharon KedarAbstract:Geophysical measurements can reveal the structures and thermal states of icy ocean worlds. The interior density, temperature, sound speed, and electrical conductivity thus characterize their habitability. We explore the variability and correlation of these parameters using 1-D internal structure models. We invoke thermodynamic consistency using available thermodynamics of aqueous MgSO_4, NaCl (as seawater), and NH_3; pure water Ice phases I, II, III, V, and VI; silicates; and any metallic core that may be present. Model results suggest, for Europa, that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by MgSO_4 from a more reduced ocean dominated by NaCl. In contrast with Jupiter's icy ocean moons, Titan and Enceladus have low-density rocky interiors, with minimal or no metallic core. The low-density rocky core of Enceladus may comprise hydrated minerals or anhydrous minerals with high porosity. Cassini gravity data for Titan indicate a high tidal potential Love number (k_2 > 0.6), which requires a dense internal ocean (ρ_(ocean) >1,200 kg m^(−3)) and icy lithosphere thinner than 100 km. In that case, Titan may have little or no high-Pressure Ice, or a surprisingly deep water-rock interface more than 500 km below the surface, covered only by Ice VI. Ganymede's water-rock interface is the deepest among known ocean worlds, at around 800 km. Its ocean may contain multiple phases of high-Pressure Ice, which will become buoyant if the ocean is sufficiently salty. Callisto's interior structure may be intermediate to those of Titan and Europa, with a water-rock interface 250 km below the surface covered by Ice V but not Ice VI.
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titan s internal structure inferred from its gravity field shape and rotation state
Icarus, 2014Co-Authors: G Tobie, R M Baland, A Lefevre, Tim Van HoolstAbstract:Abstract Several quantities measured by the Cassini-Huygens mission provide insight into the interior of Titan: the second-degree gravity field coefficients, the shape, the tidal Love number, the electric field, and the orientation of its rotation axis. The measured obliquity and tides, as well as the electric field, are evidence for the presence of an internal global ocean beneath the icy shell of Titan. Here we use these different observations together to constrain the density profile assuming a four-layer interior model (Ice I shell, liquid water ocean, high Pressure Ice mantle, and rock core). Even though the observed second degree gravity field is consistent with the hydrostatic relation J 2 = 10 C 22 / 3 , which is a necessary but not sufficient condition for a synchronous satellite to be in hydrostatic equilibrium, the observed shape of the surface as well as the non-zero degree-three gravity signal indicate some departure from hydrostaticity. Therefore, we do not restrain our range of assumed density profiles to those corresponding to the hydrostatic value of the moment of inertia (0.34). From a range of density profiles consistent with the radius and mass of the satellite, we compute the obliquity of the Cassini state and the tidal Love number k 2 . The obliquity is computed from a Cassini state model for a satellite with an internal liquid layer, each layer having an ellipsoidal shape consistent with the measured surface shape and gravity field. The observed (nearly hydrostatic) gravity field is obtained by an additional deflection of the ocean–Ice I shell interface, assuming that the layers have uniform densities. We show that the measured obliquity can be reproduced only for internal models with a dense ocean (between 1275 and 1350 kg m−3) above a differentiated interior with a full separation of rock and Ice. We obtain normalized moments of inertia between 0.31 and 0.33, significantly lower than the expected hydrostatic value (0.34). Evolutionary mechanisms leading to a significant departure from hydrostatic equilibrium while J 2 = 10 C 22 / 3 remain an open issue. The tidal Love number is found to be mostly sensitive to the ocean density and to a lesser extent to the Ice shell thickness. By combining obliquity and tidal Love number constraints, we show that the thickness of the outer Ice shell is at least 40 km and the ocean thickness is less than 100 km, with an averaged density of 1300–1350 kg m−3. The elevated density (>3400 kg m−3) found for the rocky core further suggests that it might possess a significant fraction of iron.
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titan s bulk composition constrained by cassini huygens implication for internal outgassing
The Astrophysical Journal, 2012Co-Authors: G Tobie, Daniel Gautier, F HersantAbstract:In the present report, by using a series of data gathered by the Cassini-Huygens mission, we constrain the bulk content of Titan's interior for various gas species (CH4, CO2, CO, NH3, H2S, Ar, Ne, Xe), and we show that most of the gas compounds (except H2S and Xe) initially incorporated within Titan are likely stored dissolved in the subsurface water ocean. CO2 is likely to be the most abundant gas species (up to 3% of Titan's total mass), while ammonia should not exceed 1.5 wt%. We predict that only a moderate fraction of CH4, CO2, and CO should be incorporated in the crust in the form of clathrate hydrates. By contrast, most of the H2S and Xe should be incorporated at the base of the subsurface ocean, in the form of heavy clathrate hydrates within the high-Pressure Ice layer. Moreover, we show that the rocky phase of Titan, assuming a composition similar to CI carbonaceous chondrites, is a likely source for the noble gas isotopes (40Ar, 36Ar, 22Ne) that have been detected in the atmosphere. A chondritic core may also potentially contribute to the methane inventory. Our calculations show that a moderate outgassing of methane containing traces of neon and argon from the subsurface ocean would be sufficient to explain the abundance estimated by the Gas Chromatograph Mass Spectrometer. The extraction process, implying partial clathration in the Ice layers and exsolvation from the water ocean, may explain why the 22Ne/36Ar ratio in Titan's atmosphere appears higher than the ratio in carbonaceous chondrites.
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tidal dissipation within large icy satellites applications to europa and titan
Icarus, 2005Co-Authors: G Tobie, A Mocquet, Christophe SotinAbstract:This paper describes a new approach based on variational principles to calculate the radial distribution of tidal energy dissipation in any satellite. The advantage of the model with respect to classical solutions, is that it relates in a straightforward way the radial distribution of the time-averaged dissipation rate to its sensitivity to the corresponding distribution of viscoelastic parameters. This method is applied to Io-, Europa-, and Titan-like interiors, and it is tested against the results obtained by two classical methods by determining global dissipation as well as radial and lateral distributions within satellite interiors. By exploring systematically the different parameters defining the interior models, we demonstrate that the presence of a deep ocean below an outer Ice layer strongly influences the tidal dissipation distribution in both the outer Ice layer and in the innermost part of the satellite. On the one hand, the ocean by imposing a large radial displacement at the base of the outer Ice I layer, controls the distribution of tidal strain rate within the outer layer, making the tidal strain rate field very weakly sensitive to the viscosity variations. Conversely, in the high-Pressure Ice layer below the ocean, both tidal strain rate and dissipation are very sensitive to any variation of the Ice viscosity. On the other hand, for identical structures of the mantle and of the core, the presence of a subsurface ocean reduces the strength of dissipation in the silicate mantle. The existence of a liquid layer within Europa makes models of the silicate mantle less dissipative than the predictions for Io.
Biswajit Santra - One of the best experts on this subject based on the ideXlab platform.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
Journal of Chemical Physics, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [B. Santra, J. Klimes, D. Alfe, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
arXiv: Materials Science, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
Angelos Michaelides - One of the best experts on this subject based on the ideXlab platform.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
Journal of Chemical Physics, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [B. Santra, J. Klimes, D. Alfe, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
arXiv: Materials Science, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
Roberto Car - One of the best experts on this subject based on the ideXlab platform.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
Journal of Chemical Physics, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [B. Santra, J. Klimes, D. Alfe, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.
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on the accuracy of van der waals inclusive density functional theory exchange correlation functionals for Ice at ambient and high Pressures
arXiv: Materials Science, 2013Co-Authors: Biswajit Santra, Jiři Klimes, Alexandre Tkatchenko, Dario Alfe, Ben Slater, Angelos Michaelides, Roberto Car, Matthias SchefflerAbstract:Density-functional theory (DFT) has been widely used to study water and Ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on Ice Ih and six proton ordered phases of Ice. Consistent with our previous study [Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high Pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition Pressures of the high-Pressure Ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high Pressures remains and we suggest that because of the stern test the high Pressure Ice phases pose they should be used in future benchmark studies of simulation methods for water.