| 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. |
- Hellman, Olle, et al.
(författare)
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Tuning ionic conductivity in ceria by volume optimization
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Effect of volume change on the ionic conductivity in ceria has been studied in the framework of the density functional theory. We show that properly controlling external conditions one can treat the lattice constant of ceria as an adjustable parameter and change the topology of the energy landscape for the oxygen ion diffusion. We reveal the existence of the narrow range of lattice parameters, which optimize the ionic conductivity in ceria.
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| 6. |
- Migas, D. B., et al.
(författare)
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Quasi-2D silicon structures based on ultrathin Me2Si (Me = Mg, Ca, Sr, Ba) films
- 2018
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Ingår i: Surface Science. - : Elsevier B.V.. - 0039-6028 .- 1879-2758. ; 670, s. 51-57
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Tidskriftsartikel (refereegranskat)abstract
- By means of ab initio calculations with hybrid functionals we show a possibility for quasi-2D silicon structures originated from semiconducting Mg2Si, Ca2Si, Sr2Si and Ba2Si silicides to exist. Such a 2D structure is similar to the one of transition metal chalcogenides where silicon atoms form a layer in between of metal atoms aligned in surface layers. These metal surface atoms act as pseudo passivation species stabilizing crystal structure and providing semiconducting properties. Considered 2D Mg2Si, Ca2Si, Sr2Si and Ba2Si have band gaps of 1.14 eV, 0.69 eV, 0.33 eV and 0.19 eV, respectively, while the former one is also characterized by a direct transition with appreciable oscillator strength. Electronic states of the surface atoms are found to suppress an influence of the quantum confinement on the band gaps. Additionally, we report Sr2Si bulk in the cubic structure to have a direct band gap of 0.85 eV as well as sizable oscillator strength of the first direct transition.
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| 7. |
- 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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| 8. |
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| 9. |
- 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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| 10. |
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