Ändra sökning
Avgränsa sökresultatet
1234567 51 - 100 av 458
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 51.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Derlet, P. M.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Hellman, O.
    Burakovsky, L.
    Swift, D. C.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation2009Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The new high-temperature (T), high-pressure (P), body-centered cubic (bcc) phase of iron has probably already been synthesized in recent diamond anvil cell (DAC) experiments (Mikhaylushkin et al 2007 Phys. Rev. Lett. 99 165505). These DAC experiments on iron revealed that the high-PT phase on quenching transforms into a mixture of close-packed phases. Our molecular dynamics simulation and structural analysis allow us to provide a probable interpretation of the experiments. We show that quenching of the high-PT bcc phase simulated with the embedded-atom model also leads to the formation of the mixture of close-packed phases. Therefore, the assumption of the stability of the high-PT bcc iron phase is consistent with experimental observation.

  • 52.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Dorogokupets, P. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Saxena, S. K.
    Koci, L.
    Ab initio equation of state for the body-centered-cubic phase of iron at high pressure and temperature2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The solid inner core of the Earth consists mostly of iron. There is accumulating evidence that, at the extreme pressures and temperatures of the deep Earth interior, iron stabilizes in the body-centered-cubic phase. However, experimental study of iron at those conditions is very difficult at best. We demonstrate that our ab initio approach is capable of providing volumetric data on iron in very good agreement with experiment at low temperature and high pressure. Since our approach treats high-temperature effects explicitly, this allows us to count on similar precision also at high temperature and high pressure. We perform ab initio molecular-dynamics simulations at a number of volume-temperature conditions and compute the corresponding pressures. These points are then fitted with an equation of state. A number of parameters are computed and compared with existing data. The obtained equation of state for high pressure and temperature nonmagnetic body-centered-cubic phase allows the computation of properties of iron under extreme conditions of the Earth's inner core.

  • 53.
    Belonoshko, Anatoly B.
    et al.
    KTH, Tidigare Institutioner                               , Fysik.
    Gutierrez, G.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Molecular dynamics simulation of the structure of yttria Y2O3 phases using pairwise interactions2001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6418, nr 18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied the structure of yttria (Y2O3) by means of ab initio and molecular dynamics methods. The suggested simple model for the interatomic interaction is shown to produce reasonable results at moderate pressures for a wide range of temperatures. The calculated x-ray structure factor is in good agreement with experimental data obtained by the x-ray levitation technique at the temperature of 2526 K. The quality of the agreement decreases with increasing temperature. We demonstrate that it is not necessary to assume nonstoichiometry of liquid yttria, as was done in a recent publication, to obtain agreement with experiment. The structure of liquid yttria can be considered as a mixture of 4- and 6-coordinated Y atoms. We also show the possibility of a light amorphous yttria phase, which possibly can be obtained by quenching from a vapor instead of conventional amorphous yttria quenched from a liquid.

  • 54.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Isaev, E. I.
    Skorodumova, N. V.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Stability of the body-centered-tetragonal phase of Fe at high pressure: Ground-state energies, phonon spectra, and molecular dynamics simulations2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 21Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well established that at a pressure of several megabars and low temperature Fe is stable in the hexagonal-close-packed (hcp) phase. However, there are indications that on heating a high-pressure hcp phase of Fe transforms to a less dense (open structure) phase. Two phases have been suggested as candidates for these high-temperature stable phases: namely, body-centered-cubic and body-centered-tetragonal (bct) phases. We performed first-principles molecular dynamics and phonon analysis of the bct Fe phase and demonstrated its dynamical instability. This allows us to dismiss the existence of the bct Fe phase under the high-pressure high-temperature conditions of the Earth's inner core.

  • 55.
    Belonoshko, Anatoly B.
    et al.
    KTH, Tidigare Institutioner                               , Fysik.
    LeBacq, O.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Molecular dynamics study of phase transitions in Xe2002Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 117, nr 15, s. 7233-7244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A full account is given of our recent theoretical discovery [A. B. Belonoshko, R. Ahuja, and B. Johansson, Phys. Rev. Lett. 87, 165505 (2001)] of the fcc-bcc transition in Xe at high pressure and temperature. The interaction model and method for calculating phase boundaries are exhaustively tested by independent methods. The model was carefully checked against experimental data and results of ab initio molecular dynamics and it was found to perform very well. The two-phase method employed for finding the melting transition was compared with the robust thermodynamic approach and was found to provide data in exact agreement with the latter. The deviation of the calculated melting curve from the experimental one is quite tolerable at low pressures. After a reinterpretation of the experimental data, our results are also in good agreement with recent diamond anvil cell experiments. At a pressure of around 25 GPa and a temperature of about 2700 K, we find a triple fcc-bcc-liquid point. The fcc-bcc boundary is calculated without reference to the experimental data, in contrast to our previous work, and found to be in nice agreement with previous calculations as well as with the experimental data points, which, however, were interpreted as melting. Our finding concerning the fcc-bcc transition is confirmed by the direct molecular dynamics simulation of the fcc, bcc, and liquid phases in the same computational cell. In this simulation, it was observed that while the fcc phase melts, the bcc structure solidifies. Since Xe is a typical rare-gas solid, the fcc-bcc transition can now be expected for a number of other van der Waals systems, first of all in Ar and Kr. Our finding suggests, that the transition from close packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated. The performed thorough test of methods and models in this study leads us to suggest that the original interpretation of experimental results is erroneous.

  • 56.
    Belonoshko, Anatoly B.
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Li, S.
    Ahuja, R.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    High-pressure crystal structure studies of Fe, Ru and Os2004Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 65, nr 09-aug, s. 1565-1571Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to reveal structural trends with increasing pressure in d transition metals, we performed full potential linear muffin-tin orbital calculations for Fe, Ru, and Os in the hexagonal close packed structure. The calculations cover a wide volume range and demonstrate that all these hexagonal close-packed metals have non-ideal c/a at low pressures which, however, increases with pressure and asymptotically approaches the ideal value at very high compressions. These results are in accordance with most recent experiment for Ru and Os. The experimental data for iron is not conclusive, but it is believed that the c/a ratio decreases weakly with increasing pressure at moderate compression. Since, the experimental and calculated equations of state for iron are in increasingly good agreement with increasing pressure, it is possible that either the negative c/a trend is valid only for a restricted pressure range, or related to the experimental difficulties (e.g. non-hydrostaticity).

  • 57.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Burakovsky, Leonid
    Preston, Dean L.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Melting of Fe and Fe0.9375Si0.0625 at Earth's core pressures studied using ab initio molecular dynamics2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The issue of melting of pure iron and iron alloyed with lighter elements at high pressure is critical to the physics of the Earth. The iron melting curve in the relevant pressure range between 3 and 4 Mbar is reasonably well established from the theoretical point of view. However, so far no one attempted a direct atomistic simulation of iron alloyed with light elements. We investigate here the impact of alloying the body-centered cubic (bcc) Fe with Si. We simulate melting of the bcc Fe and Fe0.9375Si0.0625 alloy by ab initio molecular dynamics. The addition of light elements to the hexagonal-close-packed (hcp) iron is known to depress its melting temperature (T-m). We obtain, in marked contrast, that alloying of bcc Fe with Si does not lead to T-m depression; on the contrary, the T-m slightly increases. This suggests that if Si is a typical impurity in the Earth's inner core, then the stable phase in the core is bcc rather than hcp.

  • 58.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, N. V.
    Bastea, S.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Shock wave propagation in dissociating low-Z liquids: D-22005Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, nr 12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 59.
    Belonoshko, Anatoly B.
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Simak, S. I.
    Kochetov, A. E.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Burakovsky, L.
    Preston, D. L.
    High-pressure melting of molybdenum2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, nr 19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting curve of the body-centered cubic (bcc) phase of Mo has been determined for a wide pressure range using both direct ab initio molecular dynamics simulations of melting as well as a phenomenological theory of melting. These two methods show very good agreement. The simulations are based on density functional theory within the generalized gradient approximation. Our calculated equation of state of bcc Mo is in excellent agreement with experimental data. However, our melting curve is substantially higher than the one determined in diamond anvil cell experiments up to a pressure of 100 GPa. An explanation is suggested for this discrepancy.

  • 60.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, N. V.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Burakovsky, L.
    Preston, D. L.
    High-pressure melting of MgSiO32005Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, nr 19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 61.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, N. V.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Melting and critical superheating2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 62.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, Natalia V.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic anisotropy of Earth's inner core2008Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 319, nr 5864, s. 797-800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Earth's solid- iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body- centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body- centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.

  • 63.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Davis, Sergio
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Ahuja, Rajeev
    Department of Physics, Uppsala University.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Simak, Sergei
    Burakovsky, Leonid
    Preston, D. L.
    Xenon melting: Density functional theory versus diamond anvil cell experiments2006Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 74, s. 054114-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed two-phase ab initio density functional theory based molecular dynamics simulations of Xe melting and demonstrated that, contrary to claims in the recent literature, the pressure dependence of the Xe melting curve is consistent with the corresponding-states theory as well as with the melting curve obtained earlier from classical molecular dynamics with a Xe pair potential. While at low pressure the calculated melting curve is in perfect agreement with reliable experiments, our calculated melting temperatures at higher pressures are inconsistent with those from the most recent diamond anvil cell experiment. We discuss a possible explanation for this inconsistency.

  • 64.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Davis, Sergio
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Skorodumova, Natalia
    Department of Physics, Uppsala University.
    Lundow, Per-Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Properties of the fcc Lennard-Jones crystal model at the limit of superheating2007Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 76, s. 064121-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The face-centered-cubic (fcc) Lennard-Jones (LJ) model can be considered as a representative model of a simple solid. We investigate the mechanism of melting at the limit of superheating in the fcc LJ solid by means of the procedure recently developed by us [Phys. Rev. B 73, 012201 (2006)]. Insight into the mechanism of melting was gained by studying diffusion and defects in the fcc LJ solid by means of molecular dynamics simulations. We found that the limit of superheating achieved by us is likely to be the highest so far. We also found that the size of the cluster which ignites the melting is very small (down to five to six atoms, depending on the size of the supercell) and closely correlates with the linear size of a supercell when the number of atoms varies between 500 and 13 500.

  • 65.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Skorodumova, Natalia
    Department of Physics, Uppsala University.
    Davis, Sergio
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Osiptsov, Alexander
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Origin of the Low Rigidity of the Earth's Inner Core2007Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, s. 1603-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Earth's solid-iron inner core has a low rigidity that manifests itself in the anomalously low velocities of shear waves as compared to shear wave velocities measured in iron alloys. Normally, when estimating the elastic properties of a polycrystal, one calculates an average over different orientations of a single crystal. This approach does not take into account the grain boundaries and defects that are likely to be abundant at high temperatures relevant for the inner core conditions. By using molecular dynamics simulations, we show that, if defects are considered, the calculated shear modulus and shear wave velocity decrease dramatically as compared to those estimates obtained from the averaged single-crystal values. Thus, the low shear wave velocity in the inner core is explained.

  • 66. Bleskov, I. D.
    et al.
    Smirnova, E. A.
    Vekilov, Y. K.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Katsnelson, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Isaev, E. I.
    Ab initio calculations of elastic properties of Ru1-xNixAl superalloys2009Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio total energy calculations based on the exact muffin-tin orbitals method, combined with the coherent potential approximation, have been used to study the thermodynamical and elastic properties of substitutional refractory Ru1-xNixAl alloys. We have found that the elastic constants C' and C11 exhibit pronounced peculiarities near the concentration of about 40 at. % Ni, which we ascribe to electronic topological transitions. Our suggestion is supported by the Fermi surface calculations in the whole concentration range. Results of our calculations show that one can design Ru-Ni-Al alloys substituting Ru by Ni (up to 40 at. %) with almost invariable elastic constants and reduced density.

  • 67. Borman, V. D.
    et al.
    Borisyuk, P. V.
    Vasiliev, O. S.
    Pushkin, M. A.
    Tronin, V. N.
    Tronin, I. V.
    Troyan, V. I.
    Skorodumova, N. V.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Observation of electron localization in rough gold nanoclusters on the graphite surface2007Ingår i: JETP Letters: Journal of Experimental And Theoretical Physics Letters, ISSN 0021-3640, E-ISSN 1090-6487, Vol. 86, nr 6, s. 393-397Artikel i tidskrift (Refereegranskat)
  • 68. Borman, V. D.
    et al.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Skorodumova, N. V.
    Tronin, I. V.
    Tronin, V. N.
    Troyan, V. I.
    Diffusion and particle mobility in 1D system2006Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 359, nr 5, s. 504-508Artikel i tidskrift (Refereegranskat)
  • 69. Borman, V. D.
    et al.
    Tronin, I. V.
    Tronin, V. N.
    Troyan, V. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Skorodumova, N. V.
    Formation of high- and low-density clusters in a 1D system2008Ingår i: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 40, nr 3, s. 643-648Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of monoatomic chains have been studied theoretically by means of statistical mechanics methods. The applied approach can be used to evaluate the interatomic distances and lifetimes of one-dimensional (1D) and quasi-1D systems. In particular, we show that the 1D clusters of gold atoms can exist in two states with different lattice parameters (similar to 3.6 and similar to 2.8 angstrom) that can explain the whole variety of experimental observations on monoatomic gold chains without assuming any wire contamination.

  • 70. Botan, V.
    et al.
    Liberman, M.
    Johansson, Börje
    Dielectric liquid phase of Bose-Einstein condensed magnetoexcitons in a double quantum well2005Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 359, s. 1439-1441Artikel i tidskrift (Refereegranskat)
  • 71. Botan, V.
    et al.
    Moskalenko, S. A.
    Johansson, Börje
    Collective elementary excitations of Bose-Einstein condensed magnetoexcitons interacting with strongly correlated electron-hole plasma2006Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 378-80, s. 1041-1042Artikel i tidskrift (Refereegranskat)
  • 72. Botan, V. V.
    et al.
    Liberman, M. A.
    Moskalenko, S. A.
    Snoke, D. W.
    Johansson, Börje
    Bose-Einstein condensation of magnetoexcitons in ideal two-dimensional system in a strong magnetic field2004Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 346, s. 460-464Artikel i tidskrift (Refereegranskat)
  • 73. Brown, R.
    et al.
    Ollerstam, A.
    Johansson, Börje
    Skott, O.
    Gebre-Medhin, S.
    Fredholm, B.
    Persson, A. E. G.
    Abolished tubuloglomerular feedback and increased plasma renin in adenosine A(1) receptor-deficient mice2001Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology, ISSN 0363-6119, E-ISSN 1522-1490, Vol. 281, nr 5, s. R1362-R1367Artikel i tidskrift (Refereegranskat)
  • 74. Burkert, T.
    et al.
    Eriksson, O.
    James, P.
    Simak, S. I.
    Johansson, Börje
    Nordstrom, L.
    Calculation of uniaxial magnetic anisotropy energy of tetragonal and trigonal Fe, Co, and Ni2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, nr 10Artikel i tidskrift (Refereegranskat)
  • 75.
    Colarieti-Tosti, Massimiliano
    et al.
    Department of Physics, Uppsala University.
    Katsnelson, M. I.
    Department of Physics, Uppsala University.
    Mattesini, M.
    Department of Physics, Uppsala University.
    Simak, S. I.
    Department of Physics, Uppsala University.
    Ahuja, Rajeev
    Department of Physics, Uppsala University.
    Johansson, Börje
    Department of Physics, Uppsala University.
    Dallera, C.
    INFM, Dipartimento di Fisica, Politecnico di Milano.
    Eriksson, O.
    Department of Physics, Uppsala University.
    First-principles theory of intermediate-valence f-electron systems2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, nr 9, s. 096403-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a first-principles based method for calculating the electronic structure and total energy of solids in an intermediate-valence configuration. The method takes into account correlation effects (d-f Coulomb interaction) and many-body renormalization of the effective hybridization parameter of the f system. As an example, the formation of a pressure-induced intermediate-valence state in Yb is considered and its electronic structure and equation of state are calculated and compared to experimental data. The agreement is found to be excellent for both properties, and we argue that the developed method, which applies to any element or compound, provides for the first time a quantitative theoretical treatment of intermediate-valence materials.

  • 76. da Silva, A. F.
    et al.
    Araujo, C. M.
    Sernelius, B. E.
    Persson, Clas
    Ahuja, R.
    Johansson, Börje
    Influence of Si doping on optical properties of wurtzite GaN2001Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, nr 40, s. 8891-8899Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The band gap shift (BGS) of Si-doped wurtzite GaN for impurity concentrations spanning the insulating to the metallic regimes has been investigated at low temperature. The critical impurity concentration for the metal-non-metal transition is estimated from the generalized Drude approach for the resistivity to be about 1.0 x 10(18) cm(-3). The calculations for the BGS were carried out within a framework of the random phase approximation, taking into account the electron-electron, electron-optical phonon, and electron-ion interactions. In the wake of very recent photoluminescence measurements, we have shown and discussed the possible transitions involved in the experimental results.

  • 77. da Silva, A. F.
    et al.
    Pepe, I.
    Persson, Clas
    KTH, Tidigare Institutioner, Materialvetenskap.
    de Almeida, J. S.
    Araujo, C. M.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    An, C. Y.
    Guo, J. H.
    Optical properties of oxide compounds PbO, SnO2 and TiO22004Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T109, s. 180-183Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The optical properties of the oxide compounds PbO and SnO2 have been investigated experimentally by transmission spectroscopy measurements and theoretically by a full-potential linearized augmented plane wave (FPLAPW) method. The dielectric functions of the rutile TiO2 has also been calculated. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results.

  • 78. Dallera, C.
    et al.
    Wessely, O.
    Colarieti-Tosti, Massimiliano
    Eriksson, O.
    Ahuja, Rajeev
    Johansson, Börje
    Katsnelson, M. I.
    Annese, E.
    Rueff, J. P.
    Vanko, G.
    Braicovich, L.
    Grioni, M.
    Understanding mixed valent materials: Effects of dynamical core-hole screening in high-pressure x-ray spectroscopy2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 8, s. 081101-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Changes in the electronic structure of Yb, a material whose valence is modified under pressure, are observed with remarkable detail in x-ray absorption and emission data measured between ambient conditions and 20 GPa. These changes are reproduced by a theory that essentially does not rely on experimental parameters, and includes dynamical core-hole screening. From the combined experimental and theoretical data we can firmly establish on a quantitative level how the valency of an intermediate valence material is modified by pressure. In metallic Yb it increases from 2 to 2.55 +/- 0.05 between 0 and 20 GPa.

  • 79.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Model for diffusion at the microcanonical superheating limit from atomistic computer simulations2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 6, s. 064102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The diffusion statistics of atoms in a crystal close to the critical superheating temperature was studied in detail using molecular dynamics and Monte Carlo simulations. We present a continuous random-walk model for diffusion of atoms hopping through thermal vacancies. The results obtained from our model suggest that the limit of superheating is precisely the temperature for which dynamic percolation happens at the time scale of a single individual jump. A possible connection between the critical superheating limit and the maximization of the Shannon entropy associated with the distribution of jumps is suggested. As a practical application of our results, we show that an extrapolation of the critical superheating temperature (and therefore an estimation of the melting point) can be performed using only the dynamical properties of the solid state.

  • 80.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    SearchFill: A stochastic optimization code for detecting atomic vacancies in crystalline and non-crystalline systems2011Ingår i: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 182, nr 5, s. 1105-1110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an implementation of a stochastic optimization algorithm applied to location of atomic vacancies. Our method labels an empty point in space as a vacancy site, if the total spatial overlap of a "virtual sphere", centered around the point, with the surrounding atoms (and other vacancies) falls below a tolerance parameter. A Metropolis-like algorithm displaces the vacancies randomly, using an "overlap temperature" parameter to allow for acceptance of moves into regions with higher overlap, thus avoiding local minima. Once the algorithm has targeted a point with low overlap, the overlap temperature is decreased, and the method works as a steepest descent optimization.

    Our method, with only two free parameters, is able to detect the correct number and coordinates of vacancies in a wide spectrum of condensed-matter systems, from crystals to amorphous solids, in fact in any given set of atomic coordinates, without any need of comparison with a reference initial structure.

  • 81.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    An atomistic model for homogeneous meltingManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The diffusion statistics of atoms in a crystal close to the critical superheating temperature wasstudied in detail using molecular dynamics (MD) and Monte Carlo (MC) simulations. We present ageneral dynamic percolation model for diffusion of atoms hopping through thermal vacancies. Theresults obtained from our model suggest that the limit of superheating is precisely the temperaturefor which dynamic percolation happens at the time scale of a single individual jump. We show thatthis prediction of the critical superheating temperature can give an estimate of the melting pointusing only the dynamical properties of the solid state.

  • 82.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    van Duin, Adri
    Johansson, Börje
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Molecular dynamics simulation of zirconia melting2010Ingår i: Central European Journal of Physics, ISSN 1895-1082, E-ISSN 1644-3608, Vol. 8, nr 5, s. 789-797Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting point for the tetragonal and cubic phases of zirconia (ZrO2) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.

  • 83.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, Natalia
    van Duin, Adri
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    High-pressure melting curve of hydrogen2008Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, s. 194508-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates considerably from density functional theory calculations. Due to this, the computed melting curve, although shares most of the known features, yields considerably lower melting temperatures compared to extrapolations of the available diamond anvil cell data. This failure of the ReaxFF model, which can reproduce many physical and chemical properties (including chemical reactions in hydrocarbons) of solid hydrogen, hints at an important change in the mechanism of interaction of hydrogen molecules in the liquid state.

  • 84.
    Delczeg, Lorand
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg, Erna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Density functional study of vacancies and surfaces in metals2011Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, nr 4, s. 045006-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We compare the performances of three common gradient-level exchange-correlation functionals for metallic bulk, surface and vacancy systems. We find that approximations which, by construction, give similar results for the jellium surface, show large deviations for realistic systems. The particular charge density and density gradient dependence of the exchange-correlation energy densities are shown to be the reason behind the obtained differences. Our findings confirm that both the global (total energy) and the local (energy density) behavior of the exchange-correlation functional should be monitored for a consistent functional design.

  • 85.
    Delczeg, Lorand
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg-Czirjak, Erna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Assessing common density functional approximations for the ab initio description of monovacancies in metals2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, nr 20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the exact muffin-tin orbitals method, we investigate the accuracy of five common density functional approximations for the theoretical description of the formation energy of monovacancies in three close-packed metals. Besides the local density approximation (LDA), we consider two generalized gradient approximation developed by Perdew and co-workers (PBE and PBEsol) and two gradient-level functionals obtained within the subsystem functional approach (AM05 and LAG). As test cases, we select aluminum, nickel, and copper, all of them adopting the face centered cubic crystallographic structure. Our results show that, compared to the recommended experimental values, LDA is be the most reliable approximation for the vacancy formation energies in these metals. However, taking into account also the performances of the functionals for the equation of state changes the final verdict in favor of the generalized gradient approximations.

  • 86.
    Delczeg, Lorand
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg-Czirjak, Erna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Tian, Fuyang
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Density functional theory of light actinides with substitutional point defects inface centered and body centered cubic descriptionsManuskript (preprint) (Övrigt vetenskapligt)
  • 87.
    Delczeg, Lorand
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio description of mono-vacancies in austenitic stainless steelsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Using a first-principles computational method, we have calculated the vacancy formation energies of paramagnetic Fe-Cr-Ni alloys as a function of chemical composition. The theoretical predictions obtained for homogeneous chemistry and relaxed nearest-neighbors are in line with the experimental observation. In particular, Ni is found to decrease and Cr increase the vacancy formation energy of the ternary system.

  • 88.
    Delczeg, Lorand
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio description of monovacancies in paramagnetic austenitic Fe-Cr-Ni alloys2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 17, s. 174101-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using first-principles alloy theory, we calculate the vacancy formation energies of paramagnetic face-centered-cubic (fcc) Fe-Cr-Ni alloys as a function of chemical composition. These alloys are well-known model systems for low carbon austenitic stainless steels. The theoretical predictions obtained for homogeneous chemistry and relaxed nearest-neighbor lattice sites are in line with the experimental observations. In particular, Ni is found to decrease and Cr to increase the vacancy formation energy of the ternary system. The results are interpreted in terms of effective chemical potentials. The impact of vacancy on the local magnetic properties of austenitic steel alloys is also investigated.

  • 89.
    Delczeg-Czirjak, Erna K.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gercsi, Z.
    Bergqvist, Lars
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, O.
    Szunyogh, L.
    Nordblad, P.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Magnetic exchange interactions in B-, Si-, and As-doped Fe2P from first-principles theory2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 22, s. 224435-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Di-iron phosphide (Fe2P) is a parent system for a set of magnetocaloric materials. Although the magnetic ordering temperature (T-C = 215 K) of the stoichiometric composition is too low for room-temperature magnetic refrigeration, the partial replacement of P with B, Si, or As elements results in a steep increase in the magnetic ordering temperature. Doping leads to different equilibrium volumes and hexagonal axial ratios (c/a) within the same crystallographic phase over a wide concentration range. Here, using first principles theory, we decompose the change in the total magnetic exchange interaction upon doping into chemical and structural contributions, the latter including the c/a-ratio and volume effects. We demonstrate that for the investigated alloys the structural effect can be ascribed mainly to the decrease in the c/a ratio that strengthens the magnetic exchange interactions between the two Fe sublattices.

  • 90.
    Delczeg-Czirjak, Erna Krisztina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Bergqvist, Lars
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, O.
    Gercsi, Z.
    Nordblad, P.
    Szunyogh, L.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Microscopic theory of magnetism in the magnetocaloric material Fe2P1-xTx (T = B and Si)2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 4, s. 045126-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Landau phenomenological theory in combination with first-principles calculations was used to reveal the origin of the metamagnetic nature and the unusually strong dependence of the ordering temperature with doping of the Fe2P compound. We show that the magnetism of the two sublattices occupied by Fe atoms has an entwined codependency, which is strongly influenced by alloying. We furthermore demonstrate that a constrained disordered local moment approach combined with Monte Carlo simulations can only reproduce the experimental ordering temperatures in these technologically important prototype alloys for magnetocaloric refrigeration.

  • 91.
    Delczeg-Czirjak, Erna Krisztina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg, Lorand
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Punkkinen, Marko Patrick John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, O.
    Division for Materials Theory, Division of Physics and Materials Science, Uppsala University.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio study of structural and magnetic properties of Si-doped Fe(2)P2010Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 82, nr 8, s. 085103-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio electronic-structure methods are used to study the properties of Fe(2)P(1-x)Si(x) in ferromagnetic and paramagnetic states. The site preference and lattice relaxation are calculated with the projector augmented wave method as implemented in the Vienna ab initio simulation package. The paramagnetic state is modeled by the disordered local magnetic moment scheme, and the chemical and magnetic disorder is treated using the coherent potential approximation in combination with the exact muffin-tin orbital formalism. The calculated lattice parameters, atomic positions, and magnetic properties are in good agreement with the experimental and other theoretical results. In contrast to the observation, for the ferromagnetic state the body centered ortho-rhombic structure (bco, space group I (mm2) under bar) is predicted to have lower energy than the hexagonal structure (hex, space group P (6) over bar 2m). The zero-point spin fluctuation energy difference is found to be large enough to stabilize the hex phase. For the paramagnetic state, the hex structure is calculated to be the stable phase and the computed total energy versus composition indicates a hex to bco crystallographic phase transition with increasing Si content. The phonon vibrational free energy, estimated from the theoretical equation of state, turns out to stabilize the hexagonal phase, whereas the electronic and magnetic entropies favor the low symmetry orthorhombic structure.

  • 92.
    Delczeg-Czirjak, Erna Krisztina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg, Lorand
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ropo, Matti
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, K.
    Department of Physics and Astronomy, University of Turku, Finland.
    Punkkinen, M.P.J
    Department of Physics and Astrononmy, University of Turku, Finland.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ab initio study of the elastic anomalies in Pd-Ag alloys2009Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio total-energy calculations, based on the exact muffin-tin orbital method, are used to determine the elastic properties of Pd1−xAgx random alloys in the face-centered-cubic crystallographic phase. The compositional disorder is treated within the coherent-potential approximation. The single crystal and polycrystalline elastic constants and the Debye temperature are calculated for the whole range of concentration, 0≤x≤1. It is shown that the variation in the elastic parameters of Pd-Ag alloys with chemical composition strongly deviates from a simple linear or parabolic trend. The complex electronic origin of these anomalies is demonstrated.

     

  • 93. Dewhurst, J. K.
    et al.
    Ahuja, Rajeev
    Li, S.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Lattice dynamics of solid xenon under pressure2002Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, nr 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use density-functional perturbation theory to obtain the phonon spectrum of fcc xenon under pressure. Thermodynamic properties obtained within the quasiharmonic approximation are in fair to good agreement with experiment at zero pressure. The transition pressure from the fcc to hcp phase is predicted to occur at 5 GPa. The fcc structure is found to be dynamically stable up to a pressure of 100 GPa, beyond which the phonon modes at the X and L symmetry points soften. We attribute the observed sluggish kinetics of the fcc-hcp transition to the small energy difference between the phases as well as to the high dynamical stability of the fcc phase.

  • 94. Dewhurst, J. K.
    et al.
    Sharma, S.
    Ambrosch-Draxl, C.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    First-principles calculation of superconductivity in hole-doped LiBC: T-c=65 K2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 2Artikel i tidskrift (Refereegranskat)
  • 95.
    Diklic, Natasa P.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Pasti, Igor
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mentus, Slavko, V
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Skorodumova, Natalia, V
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sodium storage via single epoxy group on graphene - The role of surface doping2019Ingår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 297, s. 523-528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to its unique physical and chemical properties, graphene is being considered as a promising material for energy conversion and storage applications. Introduction of functional groups and dopants on/in graphene is a useful strategy for tuning its properties. In order to fully exploit its potential, atomic-level understanding of its interaction with species of importance for such applications is required. We present a DFT study of the interaction of sodium atoms with epoxy-graphene and analyze how this interaction is affected upon doping with boron and nitrogen. We demonstrate how the dopants, combined with oxygen-containing groups alter the reactivity of graphene towards Na. Dopants act as attractors of epoxy groups, enhancing the sodium adsorption on doped oxygen-functionalized graphene when compared to the case of non-doped epoxy-graphene. Furthermore, by considering thermodynamics of the Na interaction with doped epoxy-graphene it has been concluded that such materials are good candidates for Na storage applications. Therefore, we suggest that controlled oxidation of doped carbon materials could lead to the development of advanced anode materials for rechargeable Na-ion batteries.

  • 96. Dmitriev, V. V.
    et al.
    Blanter, M. S.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio based investigation of interstitial interactions and Snoek relaxation in Nb-O2012Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 73, nr 2, s. 182-187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chemical and strain-induced effective pair interactions of interstitial oxygen atoms in bcc Nb have been determined in supercell first-principles calculations using Vienna ab initio simulation package (VASP). The strain-induced interactions are in reasonable agreement with those obtained earlier within a phenomenological microscopic Krivoglaz-Kanzaki-Khachaturyan model (KKKM). At the same time, the chemical interactions, which have been considered to be small in earlier theoretical considerations, turned out to be dominating at the first several coordination shells. The obtained interactions have been used in calculations of the concentration- and temperature-dependence of the internal friction Snoek peak. The theoretical results are found to be in good agreement with the existing experimental data.

  • 97. Dobrota, Ana S.
    et al.
    Pasti, Igor A.
    Mentus, Slavko V.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden.
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden.
    Functionalized graphene for sodium battery applications: the DFT insights2017Ingår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 250, s. 185-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Considering the increasing interest in the use of graphene-based materials for energy conversion and storage applications, we have performed a DFT study of Na interaction with doped graphene, both in non-oxidized and oxidized forms. Oxidation seems to play the crucial role when it comes to the interaction of doped graphene materials with sodium. The dopants act as attractors of OH groups, making the material prone to oxidation, and therefore altering its affinity towards Na. In some cases, this can result in hydroxide or water formation - an irreversible change lethal for battery performance. Our results suggest that one should carefully control the oxidation level of doped graphene-based materials if they are to be used as sodium battery electrode materials as the optimal oxidation level depends on the dopant type.

  • 98. Dubrovinskaia, N. A.
    et al.
    Dubrovinsky, L. S.
    Ahuja, R.
    Prokopenko, V. B.
    Dmitriev, V.
    Weber, H. P.
    Osorio-Guillen, J. M.
    Johansson, Börje
    Experimental and theoretical identification of a new high-pressure TiO2 polymorph2001Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 87, nr 27Artikel i tidskrift (Refereegranskat)
  • 99. Dubrovinskaia, N.
    et al.
    Dubrovinsky, L.
    Kantor, I.
    Crichton, W. A.
    Dmitriev, V.
    Prakapenka, V.
    Shen, G.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Beating the miscibility barrier between iron group elements and magnesium by high-pressure alloying2005Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 95, nr 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Iron and magnesium are almost immiscible at ambient pressure. The low solubility of Mg in Fe is due to a very large size mismatch between the alloy components. However, the compressibility of Mg is much higher than that of Fe, and therefore the difference in atomic sizes between elements decreases dramatically with pressure. Based on the predictions of ab initio calculations, we demonstrate in a series of experiments in a multianvil apparatus and in electrically and laser-heated diamond anvil cells that high pressure promotes solubility of magnesium in iron. At the megabar pressure range, more than 10 at. % of Mg can dissolve in Fe and then the alloy can be quenched to ambient conditions. A generality of the concept of high-pressure alloying between immiscible elements is demonstrated by its application to two other Fe group elements, Co and Ni.

  • 100. Dubrovinsky, L.
    et al.
    Dubrovinskaia, N.
    Abrikosov, I. A.
    Vennstrom, M.
    Westman, F.
    Carlson, S.
    van Schilfgaarde, M.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Pressure-induced invar effect in Fe-Ni alloys2001Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 86, nr 21, s. 4851-4854Artikel i tidskrift (Refereegranskat)
1234567 51 - 100 av 458
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf