First principles molecular dynamics simulations of diopside (CaMgSi2O6) liquid to high pressure

Sun, Ning; Stixrude, Lars; Koker, Nico de; Karki, Bijaya B.

doi:10.1016/j.gca.2011.04.004

Cited by 61 publications

(47 citation statements)

References 58 publications

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“…In fact the pressure evolution of the Sicoordination number in our simulated MORB is quite similar to the one observed in silica glass up to ~30 GPa(Benmore et al, 2010;Sato and Funamori, 2010;Zeidler et al, 2014) whereas in the 30-40GPa range the Si-coordination increases less rapidly than in silica glass (the 5-fold coordination is dominant in the simulated melt up to 40 GPa whereas a rapid increase from 5-fold to 6-fold coordination is observed in silica glass between 30 and 40 GPa). But our finding of a dominant 5-fold Si coordination in this pressure range is in agreement with the AIMD simulation data reported for liquid diopside(Sun et al, 2011) and for a MORB melt(Bajgain et al, 2015).…”

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confidence: 93%

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

et al. 2017

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International audienceA new atom-atom interaction potential is introduced for describing by classical molecular dynamics (MD) simulation the physical properties of natural silicate melts. The equation of state, the microscopic structure, the viscosity, the electrical conductivity, and the self-diffusion coefficients of ions in a mid-oceanic ridge basalt (MORB) melt are evaluated by MD over a large range of temperature and pressure (1673-3273 K and 0-60 GPa). A detailed comparison with experimental data shows that the model reproduces the thermodynamic, structural and transport properties of a MORB with an unprecedented accuracy. In particular, it is shown that the MORB melt crystallizes at lower mantle conditions into a perovskite phase whose the equation of state (EOS) is compatible with those proposed in the experimental literature. Moreover, in accordance with experimental findings, the simulation predicts not only that the MORB viscosity exhibits a (slight) minimum with the pressure, but also that the viscosity at high temperature remains very low (<100 mPa.s for T > 2273 K) even at high pressure (up to 40 GPa). However the evolution of the electrical conductivity with temperature and pressure is not always the symmetrical of that of the viscosity. In fact, the relationship between viscosity and electrical conductivity shows a crossover at around 2073 K

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confidence: 93%

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

et al. 2017

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“…A gradual fourfold to sixfold Si-O coordination change is also seen in first-principles simulations of silicate liquids, although the pressure range over which it occurs appears to be somewhat lower than that found in room-temperature compression of silicate glasses (Stixrude and Karki 2005;Sun et al 2011). Indeed, because of kinetic hindrances inherent in room-temperature compression of glass, it has long been expected that the coordination change should occur at lower pressure in silicate liquids as compared with glasses (Williams and Jeanloz 1988).…”

Section: Introductionmentioning

confidence: 82%

First-principles molecular dynamics simulations of MgSiO3 glass: Structure, density, and elasticity at high pressure

Ghosh

Karki

Stixrude

2014

American Mineralogist

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We report a first-principles molecular dynamics study of the equation of state, structural, and elastic properties of MgSiO 3 glass at 300 K as a function of pressure up to 170 GPa. We explore two different compression paths: cold compression, in which the zero pressure quenched glass is compressed at 300 K, and hot compression, in which the liquid is quenched in situ at high pressure to 300 K. We also study decompression and associated irreversible densification. Our simulations show that the glass at the zero pressure is composed of primarily Si-O tetrahedra, partially linked with each other via the bridging O atoms (present in 35%; the remaining being the non-bridging O atoms). With increasing pressure, the mean Si-O coordination number gradually increases to 6, with fivefold and subsequently sixfold replacing tetrahedra as the most abundant coordination environment. The Mg-O coordination comprising of a mixture of four-, five-, and sixfold species at zero pressure picks up more high-coordination (seven-to ninefold) species on compression and its mean value increases from 4.5 to 8 over the entire pressure range studied. Consistently, the anion-cation coordination numbers increase on compression with appearance of oxygen tri-clusters (three silicon coordinated O atoms) and mean O-Si coordination eventually reaching 2. Hot compression produces greater densities and higher coordination numbers at all pressures as compared with cold compression, reflecting kinetic hindrances to structural changes. On decompression from 6 GPa, the glass regains its initial uncompressed structure with almost no residual density. Decompression from 27 GPa produces significant irreversible compaction, and the peak-pressure of decompression significantly influences the degree of density retention with as high as 15% residual density on decompression from 170 GPa. Irreversibility arises from the survival of high coordination species to zero pressure on decompression. With increasing pressure, the calculated compressional and shear wave velocities (about 5 and 3 km/s at the ambient conditions) of MgSiO 3 glass increase initially rapidly and then more gradually at high pressures. Our results suggest that hot-compressed glasses perhaps provide closer analog to high-pressure silicate melts than the glass on cold compression.

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“…5, we find increasing coordination from ∼4 to 6 for Fe-O and 4 to 7 for Mg-O over the volume range considered here. It has been shown that number density rather than pressure or temperature is crucial to the structure of silicate liquids [48], and therefore we compare our coordination numbers to experiments at the same number density. We find ⟨Z FeO ⟩ ≈ 4.5 at 13.1Å 3 /atom, which is close to the experimental value of 5.2 at the same mean atomic volume in FeO-SiO 2 liquid at the limit of lowSiO 2 content [45,46].…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Spin crossover in liquid (Mg,Fe)O at extreme conditions

Holmström

Stixrude

2016

Phys. Rev. B

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We use first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O, whereby the magnetic moments of Fe ions vanish gradually over a range of hundreds of GPa. Because electronic entropy strongly favors the nonmagnetic low-spin state of Fe, the crossover has a negative effective Clapeyron slope, in stark contrast to the crystalline counterpart of this transition-metal oxide. Diffusivity of liquid (Mg,Fe)O is similar to that of MgO, displaying a weak dependence on element and spin state. Fe-O and Mg-O coordination increases from approximately 4 to 7 as pressure goes from 0 to 200 GPa. We find partitioning of Fe to induce a density inversion between the crystal and melt, implying separation of a basal magma ocean from a surficial one in the early Earth. The spin crossover induces an anomaly into the density contrast, and the oppositely signed Clapeyron slopes for the crossover in the liquid and crystalline phases imply that the solid-liquid transition induces a spin transition in (Mg,Fe)O.

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First principles molecular dynamics simulations of diopside (CaMgSi2O6) liquid to high pressure

Cited by 61 publications

References 58 publications

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

Properties of magmatic liquids by molecular dynamics simulation: The example of a MORB melt

First-principles molecular dynamics simulations of MgSiO3 glass: Structure, density, and elasticity at high pressure

Spin crossover in liquid (Mg,Fe)O at extreme conditions

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