Isotopic differentiation and sublattice melting in dense dynamic ice

Hermann, Andreas; Ashcroft, N. W.; Hoffmann, Roald

doi:10.1103/physrevb.88.214113

Cited by 14 publications

(16 citation statements)

References 48 publications

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“…In the P 2 1 /c phase, hydrogen bonds are neither symmetric nor linear. This is similar to what is seen in pure ice [34,51,52] and is driven by the need to reduce molecular volumes under increasing pressure. A structure that is based on the P 2 1 /c phase but features linear symmetric hydrogen bonds is, at P = 400 GPa, 0.12 eV/f.u.…”

Section: A Aluminum Oxide Hydroxidesupporting

confidence: 69%

Monoclinic high-pressure polymorph of AlOOH predicted from first principles

2016

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Aluminum oxide hydroxide, AlOOH, is a prototypical hydrous mineral in the geonomy. The study of the high-pressure phase evolution of AlOOH is of fundamental importance in helping to understand the role of hydrous minerals in the water storage and transport in Earth, as in other planets. Here, we have systematically investigated the high-pressure phase diagram of AlOOH up to 550 GPa using the efficient crystal structure analysis by particle swarm optimization (CALYPSO) algorithm in conjunction with first principles calculations. We predict a peculiar monoclinic phase (space group P 2 1 /c, 16 atoms/cell, Z = 4 ) as the most stable phase for AlOOH above 340 GPa. The occurrence of this new phase results in the breakup of symmetric linear O-H-O hydrogen bonds into asymmetric, bent O-H-O linkages and in sevenfold coordinated metal cations. The new P 2 1 /c phase turns out to be a universal high-pressure phase in group 13 oxide hydroxides, and stable for both compressed GaOOH and InOOH. The formation of the new phase in all compounds is favored by volume reduction due to denser packing.

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Section: A Aluminum Oxide Hydroxidesupporting

confidence: 69%

Monoclinic high-pressure polymorph of AlOOH predicted from first principles

2016

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“…[67] At pressures beyond the molecular phases (from 10's to 100's of GPa, as considered here) the semilocal description of PBE should become even more appropriate, as electron densities tend to become more uniform, [68] and non-bonded interactions become very similar amongst competing quasi-close-packed structures. [69] Ionic motifs under pressure. Across all phases, ionization emerges as a clear pathway towards stability with increased pressure.…”

Section: Resultsmentioning

confidence: 99%

Novel phases in ammonia-water mixtures under pressure

Robinson

Marqués

Wang

et al. 2018

The Journal of Chemical Physics

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While ammonia and water readily form hydrogen-bonded molecular mixtures at ambient conditions, their miscibility under pressure is not well understood, yet crucial e.g. to model the interior of icy planets. We report here on the behaviour of ammonia-water mixtures under extreme pressure conditions, based on first-principles calculations of 15 stoichiometries in the pressure range of 1 atm to 10 Mbar. We show that compression facilitates proton transfer from water to ammonia in all relevant mixtures. This favors ammonia-rich hydrates above 1 Mbar, stabilized by complete de-protonation of water and the formation of the unusual structural motifs O 2− •(NH + 4) 2 and O 2− •(N 2 H + 7) 2. The hydronitrogen cations persist to the highest pressures studied. We predict a new ammonia-rich 4:1-hydrate at intermediate pressures and find that by 5.5 Mbar, close to the core-mantle boundary of Neptune, all cold ammonia-water mixtures are unstable against decomposition into their constituents.

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“…Quantum effects play an essential role in the phenomenon of hydrogen bond centering; thus the description of ice VII and ice VIII transformation to the atomic ice X represents a stringent benchmark for theoretical calculations (27)(28)(29)(30)(31)(32)(33)(34)(35). First-principle calculations predict an intricate pretransitional behavior characterized by possible intermediate disordered ice X or VII phases (27)(28)(29)(30)35).…”

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confidence: 99%

Effect of salt on the H-bond symmetrization in ice

Bove

Gáal

Raza

et al. 2015

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

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The richness of the phase diagram of water reduces drastically at very high pressures where only two molecular phases, protondisordered ice VII and proton-ordered ice VIII, are known. Both phases transform to the centered hydrogen bond atomic phase ice X above about 60 GPa, i.e., at pressures experienced in the interior of large ice bodies in the universe, such as Saturn and Neptune, where nonmolecular ice is thought to be the most abundant phase of water. In this work, we investigate, by Raman spectroscopy up to megabar pressures and ab initio simulations, how the transformation of ice VII in ice X is affected by the presence of salt inclusions in the ice lattice. Considerable amounts of salt can be included in ice VII structure under pressure via rock-ice interaction at depth and processes occurring during planetary accretion. Our study reveals that the presence of salt hinders proton order and hydrogen bond symmetrization, and pushes ice VII to ice X transformation to higher and higher pressures as the concentration of salt is increased.salty ices | extreme conditions | ice bodies | H-bond symmetrization | proton quantum effects A ll models of the interior of ice bodies in the universe rely on our knowledge of the behavior of a few simple molecules under high pressure and temperature (1-22), water being the most intriguing of them, due to its abundance and its connection to life existence.New data delivered by various space missions, such as the Voyager, Galileo, and Cassini-Huygens missions, have greatly improved our understanding of the icy bodies within the solar system (23-25), and recent discoveries of extrasolar planets with significant water ice content have highlighted the importance of high-pressure H 2 O-rich phases in planetary physics beyond the solar system (26).Water displays an unusually rich pressure-temperature phase diagram, which mainly derives from the open geometry of the water molecule, which favors tetrahedral arrangements, and from the possibility of configurational disorder of the protons in the lattice. However, at high pressure (above about 2 GPa), the system experiences a large densification as a result of the interpenetration of low-pressure structures, and only two molecular phases are known, ice VIII and VII (3, 4). Ice VII is composed of two interpenetrating but not interconnected tetrahedral hydrogen-bonded networks of water molecules of normal cubic ice, Ic, with a body-centered-cubic (bcc) oxygen structure. The orientation of the water molecules is disordered, resulting in a paraelectric phase. In the antiferroelectric ice VIII phase, the water molecules and the associated dipole moments on the two sublattices possess long-range order and point in opposite directions, promoting a slight tetragonal distortion of the cubic unit cell along the staggered polarization (3, 4). In these two phases, the hydrogen bonds are characterized by a pronounced double-well proton transfer potential. Upon reducing the distance between donor and acceptor oxygens, the proton potential degenerate...

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Isotopic differentiation and sublattice melting in dense dynamic ice

Cited by 14 publications

References 48 publications

Monoclinic high-pressure polymorph of AlOOH predicted from first principles

Monoclinic high-pressure polymorph of AlOOH predicted from first principles

Novel phases in ammonia-water mixtures under pressure

Effect of salt on the H-bond symmetrization in ice

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