| 1. |
- Belonoshko, Anatoly B., et al.
(författare)
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High-pressure melting of MgSiO3
- 2005
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 94:19
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Tidskriftsartikel (refereegranskat)abstract
- The melting curve of MgSiO3 perovskite has been determined by means of ab initio molecular dynamics complemented by effective pair potentials, and a new phenomenological model of melting. Using first principles ground state calculations, we find that the MgSiO3 perovskite phase transforms into post perovskite at pressures above 100 GPa, in agreement with recent theoretical and experimental studies. We find that the melting curve of MgSiO3, being very steep at pressures below 60 GPa, rapidly flattens on increasing pressure. The experimental controversy on the melting of the MgSiO3 perovskite at high pressures is resolved, confirming the data by Zerr and Boehler.
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| 2. |
- Belonoshko, Anatoly B., et al.
(författare)
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Melting and critical superheating
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:1
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Tidskriftsartikel (refereegranskat)abstract
- Two mechanisms of melting are known, heterogeneous, where melting starts at surfaces, and homogeneous, where the liquid nucleates in the bulk crystal. If melting occurs homogeneously, a crystal can be superheated significantly above its melting temperature (T-m). At present, the physical meaning of the limit of superheating (T-LS) is unknown. We demonstrate, by molecular dynamics simulations, that the total energy of a solid at T-LS is equal to the total energy of its liquid at T-m at the same volume. In the high pressure limit T-LS and T-m are connected by the constant k(AB)=ln 2/3 via the relation k(AB)=T-LS/T-m-1.
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| 3. |
- Belonoshko, Anatoly B., et al.
(författare)
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Shock wave propagation in dissociating low-Z liquids : D-2
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:12
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Tidskriftsartikel (refereegranskat)abstract
- We present direct molecular dynamics simulations of shock wave propagation in liquid deuterium for a wide range of impact velocities. The calculated Hugoniot is in perfect agreement with the gas-gun data as well as with the most recent experimental data. At high impact velocities we observe a smearing of the shock wave front and propagation of fast dissociated molecules well ahead of the compressed region. This smearing occurs due to the fast deuterium dissociation at the shock wave front. The experimental results are discussed in view of this effect.
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| 4. |
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| 5. |
- Mikhaylushkin, A. S., et al.
(författare)
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Structural and magnetic properties of FeHx (x=0.25; 0.50; 0.75)
- 2006
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Ingår i: AIP Conf. Proc.. - : AIP. - 0735403295 - 9780735403291 ; , s. 161-167
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Konferensbidrag (refereegranskat)abstract
- The structural and magnetic properties of the FeHx (x=0.25; 0.50; 0.75) compounds have been studied using the projector augmented wave (PAW) method within the generalized gradient approximation (GGA). We compare the hcp, dhcp and fcc structures and find that for the considered concentrations of hydrogen the hcp structure is most stable in a wide pressure range. The magnetic behavior of iron is crucially influenced by hydrogen. In particular, the local moment on a Fe atom depends on the number of hydrogen atoms in the atom surroundings. Iron atoms, which are crystallographically equivalent in their original structures (hcp, fcc) but have different number of hydrogen neighbors, are shown to have different local magnetic moments. This finding suggests that the experimental observations of two magnetic moments in iron hydride can be explained by nonstoichiometry of the hydride and might not be a direct evidence for the presence of the dhcp phase.
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| 6. |
- Skorodumova, N. V., et al.
(författare)
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Electronic, bonding, and optical properties of CeO2 and Ce2O3 from first principles
- 2001
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 64:11
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Tidskriftsartikel (refereegranskat)abstract
- First-principles electronic structure calculations of cerium oxide in two forms, CeO2 and Ce2O3, are Presented. The 4f state of Ce is treated as a part of the inner core in Ce2O3 and as a valence-band-like state in CeO2,. The calculated ground-state and magnetic properties of the Ce (III) oxide are shown to be in agreement with available experimental data as well as the calculated ground-state and optical properties of Ce (IV) dioxide. The nature of the bonding in cerium oxide is discussed on the basis of an analysis of the charge-density and electron localization function distributions and described as a polarized ionic bond in both oxides.
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| 7. |
- Skorodumova, N. V., et al.
(författare)
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Influence of hydrogen on the stability of iron phases under pressure
- 2004
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 31:8, s. L08601-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of hydrogen presence on the stability of iron phases (bcc, hcp, dhcp, fcc, simple cubic) in a wide pressure interval at 0 K has been studied by the first-principles projector augmented-wave ( PAW) method. Hydrogen is shown to occupy different interstitial lattice positions depending on the type of structure and pressure. An introduction of hydrogen impurities (similar to6 at. %) leads to a stabilization of the close-packed iron structures, shifting the calculated pressure of the bcc-hcp transition from similar to9 GPa for pure iron to 7 GPa for Fe (6 at.% H). This tendency is further enhanced in the iron hydride structures. The iron hydrides in the close-packed structures (hcp, dhcp, fcc) are essentially degenerate in energy and found to be most stable in the whole pressure range.
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| 8. |
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| 9. |
- Skorodumova, N. V., et al.
(författare)
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Stability of the MgCO3 structures under lower mantle conditions
- 2005
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 90:06-maj, s. 1008-1011
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Tidskriftsartikel (refereegranskat)abstract
- The presence of carbon in the Earth makes the search for high-pressure carbon-containing phases essential for our understanding of mineral compositions of the Earth's mantle. In a recent study Isshiki et al. (2004) demonstrated that magnesite transforms into a new phase at lower mantle pressures. However, the structure of the emerging phase remained unknown. Here we show, by means of first principles calculations, that MgCO3 magnesite can transform into a pyroxene structure at 113 GPa, which further transforms into a CaTiO3-type structure at about 200 GPa.
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