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  • 251.
    Lu, Song
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hu, Qing-Miao
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Composition and orientation dependence of the interfacial energy in Fe-Cr stainless steel alloys2011Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 248, nr 9, s. 2087-2090Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a first-principles quantum mechanical method, we calculated the (001) and (110) interfacial energies between the low temperature alpha and alpha' phases of Fe-Cr alloys as functions of chemical composition. Weshow that the interfacial energies and the interfacial energy anisotropy are highly composition dependent. In particular, the increasing interfacial energy anisotropy with decreasing compositional gap may induce different morphology of the decomposed phases for different compositions of the host alloys.

  • 252.
    Lu, Song
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Qing-Miao
    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.
    Stacking fault energies of Mn, Co and Nb alloyed austenitic stainless steels2011Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, nr 14, s. 5728-5734Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of austenitic stainless steels, Fe-Cr-Ni with various Ni contents, are investigated via quantum-mechanical first-principles calculations. In the composition range (c(Cr) = 20%, 8 <= c(Ni) <= 20%, 0 <= c(Mn), c(Co), c(Nb) <= 8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0 K but increases it at room temperature in high-Ni (c(Ni) greater than or similar to 16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe-Cr-Ni alloys is inverted to an SFE-decreasing effect by Nb for c(Nb) greater than or similar to 3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE.

  • 253.
    Lu, Song
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Qing-Miao
    Punkkinen, Marko P. J.
    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.
    First-principles study of fcc-Ag/bcc-Fe interfaces2013Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 22, s. 224104-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio calculations are employed to determine the lower and upper bounds of the interfacial energy and work of separation of a fcc-Ag/bcc-Fe interface. The strain-free interfacial energy of the coherent interface is taken as the lower bound and the interfacial energy of the commensurate incoherent interface as the upper bound of the interfacial energy of a realistic semicoherent interface. The latter is estimated by applying an averaging scheme based on the interfacial energies obtained for the coherent interfaces. Similar calculations are performed for determining the bounds of the work of separation. We justify the use of the averaging scheme by carrying out large supercell calculations for a semicoherent interface. For a Fe(110)/Ag(111) semicoherent interface, we show that taking either Fe or Ag as the underlying lattice, our averaging scheme can yield a reasonable estimation of the work of separation of the semicoherent interface. However, when taking Ag as the underlying lattice, the averaged interfacial energy of the semicoherent interface is significantly underestimated due to the magnetism. The structure and magnetism at the coherent and semicoherent interfaces are discussed.

  • 254.
    Lu, Song
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Qing-Miao
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Yang, Rui
    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.
    First-principles determination of the alpha-alpha ' interfacial energy in Fe-Cr alloys2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 19, s. 195103-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interfacial energies (gamma) between the Cr-rich alpha'-FexCr1-x and Fe-rich alpha-Fe1-yCry phases (0 < x, y < 0.35) are calculated to be between similar to 0.02 and similar to 0.33 J m(-2) for the ferromagnetic state and between similar to 0.02 and similar to 0.27 J m(-2) for the paramagnetic state. Although for both magnetic states, the interfacial energy follows a general decreasing trend with increasing x and y, the fine structures of the gamma(x, y) maps exhibit a marked magnetic state dependence. The subtleties are shown to be ascribed to the magnetic interaction between the Fe and Cr atoms near the interface. The theoretical results are applied to estimate the critical grain size for nucleation and growth in Fe-Cr stainless steel alloys.

  • 255.
    Lu, Song
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhang, Hualei
    Hu, Qing-Miao
    Punkkinen, Marko P. J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Magnetic effect on the interfacial energy of the Ni(111)/Cr(110) interface2014Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, nr 35, s. 355001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The work of separation and interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface are calculated via first-principles methods. Both coherent and semicoherent interfaces are considered. We find that magnetism has a significant effect on the interfacial energy, i.e. removing magnetism decreases the interfacial energy of the semicoherent interface by around 50% . Electronic, magnetic and atomic structures at the interface are discussed. An averaging scheme is used to estimate the work of separation and interfacial energy of semicoherent interfaces based on the results of coherent interfaces. The limitations of the scheme are discussed.

  • 256. Lundin, U.
    et al.
    Sandalov, I.
    Eriksson, O.
    Johansson, Börje
    Correlation mechanism of f-electron delocalization2000Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, nr 24, s. 16370-16377Artikel i tidskrift (Refereegranskat)
  • 257. Lundin, U.
    et al.
    Sandalov, I.
    Eriksson, O.
    Johansson, Börje
    Modification of the standard model for the lanthanides2000Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 115, nr 1, s. 7-12Artikel i tidskrift (Refereegranskat)
  • 258. Lundin, U.
    et al.
    Sandalov, I.
    Johansson, Börje
    Mott-Hubbard transition in the N-orbital Hubbard model2000Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 281, s. 836-837Artikel i tidskrift (Refereegranskat)
  • 259. Luo, H. B.
    et al.
    Li, Chun-Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Q. M.
    Kulkova, S. E.
    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.
    Yang, R.
    First-principles investigations of the five-layer modulated martensitic structure in Ni(2)Mn(Al(x)Ga(1-x)) alloys2011Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, nr 15, s. 5938-5945Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the five-layer modulated (5M) martensitic structures of Ni(2)Mn(Al(x)Ga(1-x)), with x = 0, 0.1 and 0.2, are investigated by the use of the exact muffin-tin orbital method in combination with the coherent potential approximation. The 5M martensite is modeled by varying c/a (shear) and wave-like displacements of the atoms on (1 1 0) plane (shuffle) scaled by eta according to Martynov and Kokorin (J. Phys. III 2, 739 (1992)). For Ni(2)MnGa, we obtain 5M martensite with equilibrium c/a of 0.92 and eta of 0.08, in reasonable agreement with the experiment results (0.94 and 0.06, respectively). c/a and eta are linearly coupled to each other. Al-doping increases c/a and decreases eta, but the linear c/a similar to eta coupling remains. Comparing the total energies of the 5M martensite and L2(1) austenite, we find that the martensite is more stable than the austenite. Al-doping increases the relative stability of the austenite and finally becomes energetically degenerated with the 5M martensite at an Al atomic fraction (x) of about 0.26. The relative phase stability is analyzed based on the calculated density of states. The calculated total magnetic moments mu(0) as a function of c/a exhibit a maximum around the equilibrium c/a. Al-doping reduces mu(0) (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 260. Luo, H. B.
    et al.
    Li, Chun-Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Q. M.
    Yang, R.
    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.
    Theoretical investigation of the effects of composition and atomic disordering on the properties of Ni2Mn(Al1-xGax) alloy2011Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, nr 3, s. 971-980Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influences of composition and Mn-Ga/Al disordering on the magnetic and elastic properties of the Ni2Mn(Al1-xGax) Hensler alloy are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The transition temperature from the completely disordered B2 phase to the ordered L2(1) phase, estimated by the use of Bragg-Williams-Gorsky approximation, is in excellent agreement with experiments. The site-occupancy in the partially disordered alloy is determined by comparing the free energies of the alloys with different site-occupation configurations. It is found that Mn atoms generally prefer to exchange with Al atoms for the alloy with low degree of disorder and low Ga concentration. With increasing degree of disorder and Ga concentration, Mn may exchange with Ga as well. The total magnetic moment of the completely ordered alloy exhibits a minimum around x = 0.7 due to the competition between the increasing magnetic moments of Mn atoms and the decreasing moments of Ni atoms with increasing x. For the partially disordered alloy, both total and local magnetic moments of Mn and Ni decrease linearly with increasing degree of disorder, and Ga atoms show significant magnetism. The shear moduli C of the alloys are calculated with respect to both x and the degree of disorder. The results show that C decreases with increasing x and degree of disorder. The dependence on composition and on the degree of disorder of the martensitic transition temperatures is discussed in terms of the calculated C.

  • 261. Luo, Hu-Bin
    et al.
    Hu, Qing-Miao
    Li, Chun-Mei
    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.
    Yang, Rui
    Magnetic properties and temperature-dependent half-metallicity of Co2Mn(Ga(1-x)Z(x)) (Z = Si, Ge, Sn) from first-principles calculation2013Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 15, s. 156003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the first-principles exact muffin-tin orbitals method in combination with the coherent potential approximation, we investigated the magnetic properties, exchange interactions, and temperature-dependent half-metallicity of the Co2Mn(Ga(1-x)Z(x)) (Z = Si, Ge, Sn) alloys. The total magnetic moment follows perfectly a previously proposed Slater-Pauling relation, i.e., mu(0) = N-t - 24, with N-t being the number of valence electrons. The Co-Mn and Co1-Co2 (inter-sublattice) interactions are dominated by direct exchange, whereas the Co1-Co1 (intra-sublattice) interaction is characterized by superexchange. The Mn-Mn exchange interaction in Co2MnGa is of long-ranged RKKY-type. However, the Mn-Mn exchange interactions in Co(2)MnZ are relatively localized and can be attributed to superexchange. The Co-Mn, Co1-Co2 and Co1-Co1 total exchange interactions increase with x, whereas the Mn-Mn total exchange interactions show convex behavior. The calculated Curie temperature (T-C) increases with x. The ability of Z to enhance T-C follows the sequence of Si > Ge > Sn, in agreement with the experimental findings. The temperature dependence of the spin polarization at the Fermi level [P(T)] is investigated based on the disordered local moment model. P(T) drops abruptly at temperatures much lower than T-C. At temperatures higher than 200 K, the composition with higher TC generally corresponds to larger P(T).

  • 262. Luo, Hu-Bin
    et al.
    Hu, Qing-Miao
    Li, Chun-Mei
    Yang, Rui
    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.
    Phase stability of Ni-2(Mn1-xFex)Ga: A first-principles study2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 2, s. 024427-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ni-2(Mn1-xFex)Ga ferromagnetic shape memory alloy shows unusual composition-dependent martensitic transformation temperature (T-M), namely, T-M decreases with increasing e/a ratio. In hope of understanding this unusual behavior, we investigated the composition dependence of the heat of formation (H-f) and shear elastic modulus (C') of the cubic austenite as well as the stability of the five-layer modulated (5M) tetragonal martensite relative to the austenite, using first-principles exact muffin-tin orbital method in combination with coherent potential approximation. Our calculations demonstrated that H-f of the austenite increases with the Fe content x. C' increases slightly with x up to 0.05 but decreases thereafter. The composition dependence of both H-f and C' cannot fully account for the trend of T-M against x although such correlations have been proposed in literature for other Ni-Mn-Ga based alloys. The structure of 5M martensite phase of Ni-2(Mn1-xFex)Ga with 0 < x < 0.2 is determined by optimizing both the shear (changing c/a) and wavelike shuffle of atoms in (110) planes along [1 (1) over bar0] direction adopting the experimentally determined modulation function. The energy difference Delta E-AM between the austenite and 5M phases decreases with increasing x up to 0.05, following the lower Delta E-AM corresponding to lower T-M rule. However, with x larger than 0.05, Delta E-AM increases, against the experimental T-M similar to x behavior. We propose that, if taking the temperature effect and the spin-orbital coupling into account, the Delta E-AM similar to x curve might be altered and may explain the unusual composition dependence of Ni-2(Mn1-xFex)Ga.

  • 263. Luo, W.
    et al.
    Yang, S. F.
    Wang, Z. C.
    Wang, Y.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Liu, J.
    Zou, G. T.
    Structural phase transitions in brookite-type TiO2 under high pressure2005Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 133, nr 1, s. 49-53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied polycrystalline brookite TiO2 using energy-dispersive X-ray diffraction at pressures up to 27.8 GPa and derived an ambient-pressure bulk modulus of 255 GPa using Birch-Murnaghan's equations of state with a fixed value of 4 as its first derivative. The transition from brookite-type to baddeleyite-type was observed to start at 15.8 GPa and finished at 22.8 GPa. Upon decompression, the alpha-PbO2 structure appeared at 3.5 GPa and the baddeleyite-type structure remained down to 1.6 GPa. the lowest pressure in the present work.

  • 264.
    Luo, Wei
    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.
    Eriksson, Olle
    Uppsala Univ, Dept Phys, Condensed Matter Theory.
    Arapan, Sergiu
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Souvatzis, Petros
    Uppsala Univ, Dept Phys, Condensed Matter Theory.
    Katsnelson, Mikhail I.
    Radboud Univ Nijmegen, Netherlands .
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Dynamical stability of body center cubic iron at the Earth's core conditions2010Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 22, s. 9962-9964Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here, using self-consistent ab initio lattice dynamical calculations that go beyond the quasiharmonic approximation, we show that the high-pressure high-temperature bcc-Fe phase is dynamically stable. In this treatment the temperature-dependent phonon spectra are derived by exciting all the lattice vibrations, in which the phonon-phonon interactions are considered. The high-pressure and high-temperature bcc-Fe phase shows standard bcc-type phonon dispersion curves except for the transverse branch, which is overdamped along the high symmetry direction Gamma-N, at temperatures below 4,500 K. When lowering the temperature down to a critical value T-C, the lattice instability of the bcc structure is reached. The pressure dependence of this critical temperature is studied at conditions relevant for the Earth's core.

  • 265. Magyari-Kope, B.
    et al.
    Vitos, L.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Kollar, J.
    High-pressure structure of ScAlO3 perovskite2002Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, nr B7Artikel i tidskrift (Refereegranskat)
  • 266. Magyari-Kope, B.
    et al.
    Vitos, L.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Kollar, J.
    Parametrization of perovskite structures: an ab initio study2001Ingår i: Acta Crystallographica Section B: Structural Science, ISSN 0108-7681, E-ISSN 1600-5740, Vol. 57, s. 491-496Artikel i tidskrift (Refereegranskat)
  • 267. Magyari-Kope, B.
    et al.
    Vitos, Levente
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Grimvall, G.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Kollar, J.
    Low-temperature crystal structure of CaSiO3 perovskite: An ab initio total energy study2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stability of cubic CaSiO3 perovskite with respect to octahedral rotations is investigated by ab initio total-energy calculations. The proposed theoretical ground-state crystal structure has the orthorhombic Pbnm symmetry. Pressure gradually reduces the average tilting of the SiO6 octahedra relative to the cubic axis, from 7degrees at zero pressure to 4degrees at about 150 GPa. The energy difference between the orthorhombic and cubic phases at 0 GPa is 63 meV per f.u. and shows weak pressure dependence. A possible stabilization of the cubic phase at finite temperatures by entropy effects is discussed.

  • 268. Magyari-Kope, B.
    et al.
    Vitos, Levente
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Kollar, J.
    Model structure of perovskites: cubic-orthorhombic phase transition2002Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 25, nr 4, s. 615-621Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We extend the revised global parametrization method (revGPM) of orthorhombic perovskites with Pbnm symmetry to describe the changes in the lattice parameters and internal atomic coordinates within a broad range of structural distortions, including the vicinity of the orthorhombic-cubic phase transition. The applicability of the revGPM in the prediction of the evolution of the structural parameters under increasing hydrostatic pressure is demonstrated through test calculations performed for geophysically important perovskites. The present results are compared with the available theoretical and experimental data.

  • 269. Magyari-Kope, B.
    et al.
    Vitos, Levente
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Kollar, J.
    Origin of octahedral tilting in orthorhombic perovskites2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, nr 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adopted crystal structure of the ABO(3) perovskites is determined by the balance between the interaction of the semicore states of the A and B atoms and oxygen ions. Topological considerations show that the structural setup always stabilizes the cubic phase at large pressures, while small or negative pressures favor nonvanishing octahedral tiltings. As an example, we show that the structural distortion in CaSiO3 perovskite is slightly depressed with hydrostatic pressure, but it increases significantly with increasing volume.

  • 270. Mattesini, M.
    et al.
    Ahuja, Rajeev
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Cubic Hf3N4 and Zr3N4: A class of hard materials2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report ab initio computer modeling of the high-pressure cubic forms of Zr3N4 and Hf3N4. Equilibrium structural parameters were derived at 0 K and zero pressure for different exchange-correlation functionals. Single crystal elastic constants and bulk moduli were then computed at the athermal limit in order to quantify the stiffness of the investigated nitrides. We find that Hf3N4 should have a Vickers hardness similar to that of Si3N4.

  • 271. Mattesini, M.
    et al.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Sa, L.
    Hugosson, Håkan Wilhelm
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, O.
    Electronic structure and optical properties of solid C-602009Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 404, nr 12-13, s. 1776-1780Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure and the optical properties of face-centered-cubic C-60 have been investigated by using an all-electron full-potential method. Our ab initio results show that the imaginary dielectric function for high-energy values looks very similar to that of graphite, revealing close electronic structure similarities between the two systems. We have also identified the origin of different peaks in the dielectric function of fullerene by means of the calculated electronic density of states. The computed optical spectrum compares fairly well with the available experimental data for the Vis-UV absorption spectrum of solid C-60.

  • 272. Mattesini, M.
    et al.
    de Almeida, J. S.
    Dubrovinsky, L.
    Dubrovinskaia, N.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Ahuja, R.
    Cubic TiO2 as a potential light absorber in solar-energy conversion2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Materials are currently sought for use in the photo-induced decomposition of water on crystalline electrodes. Titanium dioxide is valuable in this respect. The electronic structural properties of cubic TiO2 polymorphs were investigated by means of first-principles methods. We demonstrate that both fluorite- and pyrite-type TiO2 have important optical absorptive transitions in the region of the visible light. A cubic TiO2 phase that can efficiently absorb the sunlight would be an important candidate material for the development of the solar cells. Also, we present results on the Ti L edges for the two different titania forms. We predict that a qualitative spectroscopic discrimination of the cubic polymorphs can be achieved by following the Ti 2p → 3d x-ray transitions.

  • 273. Mattesini, M.
    et al.
    de Almeida, J. S.
    Dubrovinsky, L.
    Dubrovinskaia, N.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Ahuja, R.
    High-pressure and high-temperature synthesis of the cubic TiO2 polymorph2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 21Artikel i tidskrift (Refereegranskat)
  • 274. Mikhaylushkin, A. S.
    et al.
    Abrikosov, I. A.
    Belonoshko, Anatoly B.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Simak, S. I.
    Instability of the body-centered tetragonal phase of iron under extreme conditions2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of the tetragonal and orthorhombic axial distortions on the body-centered cubic (bcc) phase of Fe at extreme conditions has been studied by means of first-principles calculations. We unambigiously demonstrate that the energy minimum corresponding to the body-centered tetragonal (bct) (c/a approximate to 0.9) structure, previously found in Fe upon the axial tetragonal distortion of the bcc phase along the Bain's path under compression at zero temperature, is an artifact of the structural constraint. When the bcc structure is examined using the orthorhombic distortion involving the tetragonal distortion as a particular case, the bct (c/a approximate to 0.9) structural framework represents a saddle point between two mirrored face-centered cubic minima rather than a local minimum. Therefore we conclude that there is no ground to emphasize on possible thermal stabilization of the bct structure with a particular c/a ratio apart from the whole family of structures obtained by tetragonal, orthorhombic, or another type of axial distortions.

  • 275. Mikhaylushkin, A. S.
    et al.
    Haussermann, U.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Simak, S. I.
    Fluctuating lattice constants of indium under high pressure2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, nr 19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent high-pressure investigations of elemental In have yielded controversial results. We show that the observed high-pressure face-centered orthorhombic (fco) structure can be explained as an intermediate state between two body-centered tetragonal (bct) structures with different c/a ratios (c/a < &RADIC;2 and c/a > root2, respectively). In a pressure range from about 50 to 200 GPa these two bct structures correspond to local minima of the total energy with respect to orthorhombic distortion of the ground-state bct In structure. The fco saddle point represents a tiny barrier and even at low temperatures rapid structural fluctuations should occur. Such a situation has not been identified in any other elemental metal.

  • 276. Mikhaylushkin, A. S.
    et al.
    Simak, S. I.
    Burakovsky, L.
    Chen, S. P.
    Johansson, Börje Örje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Preston, D. L.
    Swift, D. C.
    Belonoshko, Anatoly B.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mikhaylushkin et al. Reply2008Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 101, nr 4, s. 049602-Artikel i tidskrift (Refereegranskat)
  • 277. Mikhaylushkin, A. S.
    et al.
    Simak, S. I.
    Dubrovinsky, L.
    Dubrovinskaia, N.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Pure iron compressed and heated to extreme conditions2007Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, nr 16Artikel i tidskrift (Refereegranskat)
  • 278. Mikhaylushkin, A. S.
    et al.
    Simak, S. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Haussermann, U.
    Electron-concentration and pressure-induced structural changes in the alloys In1-xXx (X= Cd,Sn)2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 13Artikel i tidskrift (Refereegranskat)
  • 279. Mikhaylushkin, A. S.
    et al.
    Simak, S. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Haussermann, U.
    High-pressure behavior of phosphorus from first principles calculations2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 9Artikel i tidskrift (Refereegranskat)
  • 280. Mikhaylushkin, A. S.
    et al.
    Simak, S. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Haussermann, U.
    The role of orthorhombic distortions in gallium under high hydrostatic pressure2006Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 67, nr 10-sep, s. 2132-2135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have performed a detailed analysis ofthedouble-well feature ofthetotal energy fortheGa-III phase as a function of tetragonal andorthorhombicdistortionsoftheface-centered cubic (fcc) lattice. We demonstrate that inthelow-pressureregion this double-well feature disappears and only one minimum exists. In order to reveal this result,thepossibility oforthorhombicdistortionshas to be taken into account. At elevatedpressurebetween 58 and 84 GPa,thesecond minimum becomes pronounced, but never develops into a separate local minimum up tothetransformation intothefcc phase.

  • 281. Mikhaylushkin, A. S.
    et al.
    Skorodumova, N. V.
    Ahuja, R.
    Johansson, Börje S.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Structural and magnetic properties of FeHx (x=0.25; 0.50; 0.75)2006Ingår i: AIP Conf. Proc., 2006, s. 161-167Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 282. Mirbt, S.
    et al.
    Sanyal, B.
    Isheden, C.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    First-principles calculations of Fe on GaAs(100)2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, nr 15Artikel i tidskrift (Refereegranskat)
  • 283. Mohn, P.
    et al.
    Weinberger, P.
    Ujfalussy, B.
    Eriksson, O.
    Gutierrez, G.
    Ahuja, R.
    Johansson, Börje
    Comment on Mystery of the alkali metals: Giant moments of Fe and Co on and in Cs films2000Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 85, nr 7, s. 1583-1583Artikel i tidskrift (Refereegranskat)
  • 284. Moskalenko, S. A.
    et al.
    Liberman, M. A.
    Snoke, D. W.
    Botan, V. V.
    Johansson, Börje
    Bose-Einstein condensation of excitons in ideal two-dimensional system in a strong magnetic field2003Ingår i: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 19, nr 3, s. 278-288Artikel i tidskrift (Refereegranskat)
  • 285. Moysés Araújo, C.
    et al.
    Kapilashrami, Mukes
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jun, Xu
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jayakumar, Onattu D.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nagar, Sandeep
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Wu, Yan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Århammar, Cecilia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rao, K Venkat.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Unusual ferromagnetism above room temperature in undoped thin films and nanoparticles of MgOManuskript (Övrigt vetenskapligt)
  • 286. Nabi, Z.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ab initio calculation of elastic properties of solid He under pressure - art. no. 10721022005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high-pressure equation of state and elastic properties of solid He (He-4) have been calculated using density functional theory formulated in the framework of the exact muffin-tin orbitals method. The theoretical results, obtained within the generalized gradient approximation for the exchange-correlation functional, are in good agreement with the experimental data available for pressures between 13 GPa and 32 GPa. We predict that at 0 K the hexagonal phase of He remains mechanically and thermodynamically stable up to the highest pressure considered in the present study (similar to 150 GPa). The calculated anisotropy ratios of He are similar to those observed in the case of hexagonal metals with c/a similar to 1.63. On the other hand, we find that hydrostatic pressure has negligible effect on the anisotropy of He. This indicates that He can be used as a quasihydrostatic medium in high-pressure experiments up to at least 150 GPa.

  • 287.
    Narsu, B.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Wang, Gui-Sheng
    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.
    Large magneto-chemical-elastic coupling in highly magnetostrictive Fe-Ga alloys2013Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, nr 23, s. 231903-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The strong softening of the tetragonal shear elastic constant (C') is the main reason for the second magnetostriction peak observed in Fe100-xGax alloys. Here, we study the coupling between chemical order and magnetism with the aim to understand the origin of the elastic softening. We demonstrate that C' strongly depends on the degree of order of Ga atoms in alpha-Fe. The B-2 type ordering proves to have an important role on the elastic softening for x < 19%, whereas the extreme shear lattice softening and the anomalous temperature dependence of C' are found to be due to the strong magnetochemical coupling in the DO3 phase.

  • 288. Niklasson, A. M. N.
    et al.
    Wills, J. M.
    Katsnelson, M. I.
    Abrikosov, I. A.
    Eriksson, O.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Modeling the actinides with disordered local moments2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, nr 23Artikel i tidskrift (Refereegranskat)
  • 289.
    Noura, Al-Zoubi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Skorodumova, Natalia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Medvedeva, A.
    Andersson, J.
    Nilson, G.
    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.
    Tetragonlity of carbon-doped ferromagnetic iron alloys: a first-priniciples studyIngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453Artikel i tidskrift (Övrigt vetenskapligt)
  • 290.
    Odell, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Bock, N.
    Challacombe, M.
    Niklasson, Anders M. N.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Higher-order symplectic integration in Born-Oppenheimer molecular dynamics2009Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The extended Lagrangian formulation of time-reversible Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, C. J. Tymczak, and M. Challacombe, Phys. Rev. Lett. 100, 123004 (2008); Phys. Rev. Lett. 97, 123001 (2006)] enables the use of geometric integrators in the propagation of both the nuclear and the electronic degrees of freedom on the Born-Oppenheimer potential energy surface. Different symplectic integrators up to the sixth order have been adapted and optimized in the framework of ab initio self-consistent-field theory. It is shown how the accuracy can be significantly improved compared to a conventional Verlet integration at the same level of computational cost, in particular, for the case of very high accuracy requirements.

  • 291.
    Odell, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Cawkwell, Marc J
    LANL, Los Alamos, USA.
    Niklasson, Anders M N
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Geometric integration in Born-Oppenheimer molecular dynamics2011Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, nr 22, s. 224105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Geometric integration schemes for extended Lagrangian self-consistent Born-Oppenheimer moleculardynamics, including a weak dissipation to remove numerical noise, are developed and analyzed.The extended Lagrangian framework enables the geometric integration of both the nuclear and electronicdegrees of freedom. This provides highly efficient simulations that are stable and energy conservingeven under incomplete and approximate self-consistent field (SCF) convergence. We investigatethree different geometric integration schemes: (1) regular time reversible Verlet, (2) secondorder optimal symplectic, and (3) third order optimal symplectic. We look at energy conservation,accuracy, and stability as a function of dissipation, integration time step, and SCF convergence. Wefind that the inclusion of dissipation in the symplectic integration methods gives an efficient dampingof numerical noise or perturbations that otherwise may accumulate from finite arithmetics in aperfect reversible dynamics.

  • 292.
    Odell, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Cawkwell, Marc
    Theoretical Division, Los Alamos National Laboratory.
    Niklasson, Anders M. N.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Geometric integration in extended lagrangian self consistent tight-binding molecular dynamicsArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Geometric integration schemes for extended Lagrangian self-consistent tight-binding molecular dynamics, including a weak dissipation to remove numerical noise, are developed and analyzed. The extended Lagrangian framework enables the geometric integration of both the nuclear andelectronic degrees of freedom. This provides highly effcient simulations that are stable and energy conserving even under incomplete and approximate self-consistent field (SCF) convergence. We investigate three different geometric integration schemes: i) regular time reversible Verlet, ii) secondorder optimal symplectic, and iii) third order optimal symplectic. We look at energy conservation, accuracy and stabilitty as a function of dissipation, integration time step, and SCF convergence. We find that the inclusion of dissipation in the symplectic integration methods gives an efficient damping of numerical noise or perturbations that otherwise may accumulate from finite arithmetics in a perfect reversible dynamics. The modification of the integration breakes symplecticity and introduces a global energy drift. The systematic drift in energy and the broken symplecticity can be kept arbitrarily small without significant perturbations of the molecular trajectories. However, we have yet to find a formalism for the inclusion of the dissipation in higher-order symplectic integration methods with a more optimal balance between efficient damping and minimal global energy drift.

  • 293.
    Odell, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rungger, Ivan
    School of Physics and CRANN, Trinity College, Dublin.
    Sanvito, Stefano
    School of Physics and CRANN, Trinity College, Dublin.
    Investigation of the Conducting Properties of a Photoswitching Dithienylethene Molecule2010Ingår i: ACS NANO, ISSN 1936-0851, Vol. 4, nr 5, s. 2635-2642Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Photoswitching molecules are attractive candidates as organic materials for optoelectronics applications because light impulses can switch them between states with different conducting characteristics. Here, we report a fully self-consistent density functional theory calculation of the electron transport properties of photoswitching dithienylethene attached to Au leads in both the open and closed conformations. The molecule is found to be a good conductor in both conformations, with the low-bias current for the closed one being about 20 times larger than that of the open. Importantly, the current voltage characteristics away from the linear response are largely determined by molecular orbital rehybridization in an electric field, in close analogy to what happens for Mn-12 molecules. However, in the case of dithienylethene attached to Au, such a mechanism is effective also in conditions of strong electronic coupling to the electrodes. This makes the dithienylethene family an intriguing materials platform for constructing highly conducting organic optoelectronics switches.

  • 294.
    Odell, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ulman, Kanchan
    Jawaharlal Nehru Centre for Advanced Scientic Research Jakkur.
    Narasimhan, Shobana
    Jawaharlal Nehru Centre for Advanced Scientic Research Jakkur.
    Rungger, Ivan
    School of Physics and CRANN, Trinity College.
    Sanvito, Stefano
    School of Physics and CRANN, Trinity College.
    Comparison between s- and d-electron mediated transport in a photoswitching dithienylethene molecule using ab initio transport methods2011Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 84, nr 16, s. 165402-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of the electrode's Fermi surface on the transport properties of a photoswitching molecule is investigated with state-of-the-art ab initio transport methods. We report results for the conducting properties of the two forms of dithienylethene attached either to Ag or to nonmagnetic Ni leads. The I-V curves of the Ag/dithienylethene/Ag device are found to be very similar to those reported previously for Au. In contrast, when Ni is used as the electrode material the zero-bias transmission coefficient is profoundly different as a result of the role played by the Ni d bands in the bonding between the molecule and the electrodes. Intriguingly, despite these differences the overall conducting properties depend little on the electrode material. We thus conclude that electron transport in dithienylethene is, for the cases studied, mainly governed by the intrinsic electronic structure of the molecule.

  • 295. Olovsson, W.
    et al.
    Abrikosov, I. A.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Core level shift in random CuPd and AgPd alloys by the complete screening picture2002Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 127, nr 02-jan, s. 65-69Artikel i tidskrift (Refereegranskat)
  • 296. Olovsson, W.
    et al.
    Abrikosov, I. A.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Newton, A.
    Cole, R. J.
    Weightman, P.
    Auger energy shifts in fcc AgPd random alloys from complete screening picture and experiment2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, nr 22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Augerkinetic energyand Augerparameter shiftsin fccAgPdrandomalloyswere calculated by extending the completescreeningpicture. The augerkinetic energyshiftfor the L3M4,5M4,5 Auger transition was calculated ab initio and compared with first-principles calculations. The shifts were analyzed as a function of alloy compositions. The Auger kinetic energy shifts were also analyzed in terms of single-hole states for the 2p3/2 core level and double-hole states for the 3d 5/2 core level.

  • 297. Olovsson, W.
    et al.
    Bech, L.
    Andersen, T. H.
    Li, Z.
    Hoffmann, S. V.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Onsgaard, J.
    Core-level shifts for two- and three-dimensional bimetallic PdxCu1-x and PdxAg1-x alloys on Ru(0001)2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 7Artikel i tidskrift (Refereegranskat)
  • 298. Olovsson, W.
    et al.
    Goransson, C.
    Pourovskii, L. V.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Core-level shifts in fcc random alloys: A first-principles approach2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 6Artikel i tidskrift (Refereegranskat)
  • 299. Olovsson, Weine
    et al.
    Marten, Tobias
    Holmström, Erik
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, Igor A.
    First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids2010Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 178-179, nr C, s. 88-99Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a brief overview of recent theoretical studies of the core-level binding energy shift (CLS) in solid metallic materials. The focus is on first principles calculations using the complete screening picture, which incorporates the initial (ground state) and final (core-ionized) state contributions of the electron photoemission process in X-ray photoelectron spectroscopy (XPS), all within density functional theory (DFT). Considering substitutionally disordered binary alloys, we demonstrate that on the one hand CLS depend on average conditions, such as volume and overall composition, while on the other hand they are sensitive to the specific local atomic environment. The possibility of employing layer resolved shifts as a tool for characterizing interface quality in fully embedded thin films is also discussed, with examples for CuNi systems. An extension of the complete screening picture to core-core-core Auger transitions is given, and new results for the influence of local environment effects on Auger kinetic energy shifts in fcc AgPd are presented.

  • 300. Osorio-Guillen, J. M.
    et al.
    Ahuja, Rajeev
    KTH, Tidigare Institutioner, Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Structural phase transitions in heavy alkali metals under pressure2004Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 5, nr 9, s. 1411-1415Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed a theoretical study of the crystal structures of cesium and rubidium under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs lll and Rb lll phases. The calculated transition pressures agree extremely well with the measured data. Thus, it is now certain that the famous isostructural phase transition in cesium is actually a new crystallographic phase transition. A d-orbital occupation number of about 0.52 is crucial for the occurrence of these complex structures.

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