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  • 51.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Unconventional Rotational Responses of Hadronic Superfluids in a Neutron Star Caused by Strong Entrainment and a Sigma(-) Hyperon Gap2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 23Article in journal (Refereed)
    Abstract [en]

    I show that the usual model of the rotational response of a neutron star, which predicts rotation-induced neutronic vortices and no rotation-induced protonic vortices, does not hold (i) beyond a certain threshold of entrainment interaction strength nor (ii) in the case of nonzero Sigma(-) hyperon gap. I show that in both of these cases the rotational response involves the creation of phase windings in an electrically charged condensate. Lattices of bound states of vortices which result from these phase windings can (for a range of parameters) strongly reduce the interaction between rotation-induced vortices with magnetic-field carrying superconducting components.

  • 52.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Ashcroft, N. W.
    Violation of the London law and Onsager-Feynman quantization in multicomponent superconductors2007In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 3, no 8, p. 530-533Article in journal (Refereed)
    Abstract [en]

    Non-classical response to rotation is a hallmark of quantum ordered states such as superconductors and superfluids. The rotational responses of all currently known single-component 'super' states of matter (superconductors, superfluids and supersolids) are largely described by two fundamental principles and fall into two categories according to whether the systems are composed of charged or neutral particles: the London law relating the angular velocity to a subsequently established magnetic field and the Onsager-Feynman quantization of superfluid velocity. These laws are theoretically shown to be violated in a two-component superconductor such as the projected liquid metallic states of hydrogen and deuterium at high pressures. The rotational responses of liquid metallic hydrogen or deuterium identify them as a new class of dissipationless states; they also directly point to a particular experimental route for verification of their existence.

  • 53.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Carlström, Johan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Type-1.5 superconductivity in two-band systems2010In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 470, no 19, p. 717-721Article in journal (Refereed)
    Abstract [en]

    In the usual Ginzburg-Landau theory the critical value of Ginzburg-Landau parameter kappa(c) = 1/root 2 separates regimes of type-I and type-II superconductivity. The latter regime possess thermodynamically stable vortex excitations which interact with each other repulsively and tend to form vortex lattices. It was shown in [5] that this dichotomy in broken in U(1) x U(1) Ginzburg-Landau models which possess a distinct phase with vortex excitations which interact attractively at large length scales and repulsively at shorter distances. Here we discuss the influence of the Josephson coupling and that similar kind of superconductivity can also arise for entirely different reasons in superconductors where only one band is superconducting if this band interacting via a proximity effect with another band (the report is partially based on [1]).

  • 54.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Carlström, Johan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Garaud, J.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Speight, J. M.
    Type-1.5 superconductivity in multiband systems: Magnetic response, broken symmetries and microscopic theory - A brief overview2012In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 479, p. 2-14Article in journal (Refereed)
    Abstract [en]

    A conventional superconductor is described by a single complex order parameter field which has two fundamental length scales, the magnetic field penetration depth lambda and the coherence length xi. Their ratio kappa determines the response of a superconductor to an external field, sorting them into two categories as follows; type-I when kappa < 1/root 2 and type-II when kappa > 1/root 2. We overview here multicomponent systems which can possess three or more fundamental length scales and allow a separate "type-1.5" superconducting state when, e. g. in two-component case xi(1) < root 2 lambda < xi(2). In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges. As a consequence the system should form an additional Semi-Meissner state which properties we discuss below. In that state vortices form clusters in low magnetic fields. Inside the cluster one of the component is depleted and the superconductor-to-normal interface has negative energy. In contrast the current in second component is mostly concentrated on the cluster's boundary, making the energy of this interface positive. Here we briefly overview recent developments in Ginzburg-Landau and microscopic descriptions of this state.

  • 55.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Carlström, Johan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Speight, Martin
    Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 6, p. 067003-Article in journal (Refereed)
    Abstract [en]

    We show that in multiband superconductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response to low magnetic fields leading to phase separation into domains of two-component Meissner states and vortex droplets.

  • 56.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Jaykka, Juha
    Speight, Martin
    Magnetic Field Delocalization and Flux Inversion in Fractional Vortices in Two-Component Superconductors2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 23Article in journal (Refereed)
    Abstract [en]

    We demonstrate that, in contrast with the single-component Abrikosov vortex, in two-component superconductors vortex solutions with an exponentially screened magnetic field exist only in exceptional cases: in the case of vortices carrying an integer number of flux quanta and in a special parameter limit for half-quantum vortices. For all other parameters, the vortex solutions have a delocalized magnetic field with a slowly decaying tail. Furthermore, we demonstrate a new effect which is generic in two-component systems but has no counterpart in single-component systems: on exactly half of the parameter space of the U(1)xU(1) Ginzburg-Landau model, the magnetic field of a generic fractional vortex inverts its direction at a certain distance from the vortex core.

  • 57.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Comment on "Ginzburg-Landau theory of two-band superconductors: Absence of type-1.5 superconductivity"2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 1, p. 016501-Article in journal (Other academic)
    Abstract [en]

    The recent paper by V. G. Kogan and J. Schmalian [Phys. Rev. B 83, 054515 (2011)] argues that the widely used two-component Ginzburg-Landau (GL) models are not correct, and further concludes that in the regime which is described by a GL theory there could be no disparity in the coherence lengths of two superconducting components. This would in particular imply that [in contrast to U(1) x U(1) superconductors] there could be no "type-1.5" superconducting regime in U(1) multiband systems for any finite interband coupling strength. We point out that these claims are incorrect and based on an erroneous scheme of reduction of a two-component GL theory.

  • 58.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Type-1.5 Superconductivity in Multiband and Other Multicomponent Systems2013In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 26, no 5, p. 2045-2055Article in journal (Refereed)
    Abstract [en]

    Usual superconductors are classified into two categories: of type-1 when the ratio of the magnetic field penetration length (lambda) to coherence length (xi) kappa = lambda/xi < 1/root 2 and of type-2 when kappa > 1/root 2. The boundary case kappa = 1/root 2 is also considered to be a special situation, frequently termed as "Bogomolnyi limit". Here we discuss multicomponent systems which can possess three or more fundamental length scales and allow a separate superconducting state, which was recently termed "type-1.5". In that state, a system has the following hierarchy of coherence and penetration lengths xi(1) < root 2 lambda < xi(2). We also briefly overview the works on single-component regime kappa approximate to 1/root 2 and comment on recent discussion by Brandt and Das in the proceedings of the previous conference in this series.

  • 59.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Svistunov, Boris
    Rotational response of superconductors: Magnetorotational isomorphism and rotation-induced vortex lattice2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 10, p. 104501-Article in journal (Refereed)
    Abstract [en]

    The analysis of nonclassical rotational response of superfluids and superconductors was performed by Onsager [Onsager, Nuovo Cimento, Suppl. 6, 279 (1949)] and London [Superfluids (Wiley, NewYork, 1950)] and crucially advanced by Feynman [Prog. Low Temp. Phys. 1, 17 (1955)]. It was established that, in the thermodynamic limit, neutral superfluids rotate by forming-without any threshold-a vortex lattice. In contrast, the rotation of superconductors at angular frequency Omega-supported by uniform magnetic field B-L proportional to Omega due to surface currents-is of the rigid-body type (London law). Here we show that, neglecting the centrifugal effects, the behavior of a rotating superconductor is identical to that of a superconductor placed in a uniform fictitious external magnetic field (H) over tilde = -B-L. In particular, the isomorphism immediately implies the existence of two critical rotational frequencies in type-2 superconductors.

  • 60.
    Backlund, Karl-Oskar
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Deriving an extended one-band Hubbard model for cuprate superconductors2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The so-called three-band Hubbard model is generally believed to be a good model for fermions on a CuO 2 lattice and to contain key features allowing to understand high-temperature superconductivity in the cuprates. A simpler and more popular model is the one-band Hubbard model. In this thesis,an extended one-band Hubbard model is derived from the three-band model.

    First, some mathematical background is given, as well as an introduction to Hubbard-like models. Then, to derive the extended one-band Hubbard model, the CuO 2 lattice is divided into clusters of one Cu and two O sites, and a variant of the Feshbach method is used to replace each such cluster by a single lattice site. To nd a suitable one-band model, all Hamiltonian matrix elements are matched between the two models. Finally, dierent sets of three-band parameters are considered, and it is studied how this aects the parameters in the extended one-band Hubbard model.

  • 61.
    Backman, Carl-Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Wennberg, Johannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Quantum Mechanical Conduction of Electrons in 1DFibonacci Quasicrystals2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this report we model and study the propagation of electrons in one-dimensional (1D)

    Fibonacci quasicrystals. The quasicrystals are modeled with delta function potentials and

    created by either arranging their strengths or their spacings as a 2 letter Fibonacci word.

    The transmission and reflection amplitudes are calculated using an iterative method.

    A comparison is made against an ordinary crystal and a semi-random setup. The

    transmission of electrons are investigated and related to the electrical conduction in the

    different types of materials. We also investigate how sensitive the quasicrystals are to

    perturbations, compared to crystals. Finally, a quasicrystal modeled with a 3 letter

    Fibonacci word is discussed.

    We find that the Fibonacci structure increases the resistance by a relatively large

    factor, which makes the quasicrystals act like semiconductors. We also find tendencies

    that the quasicrystals are more sensitive to perturbations compared to ordinary crystals.

    The results are in good agreement with similar, earlier studies, both theoretical and experimental.

  • 62. Basylko, S. A.
    et al.
    Lundow, Per Håkan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    One-dimensional Kondo lattice model studied through numerical diagonalization2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 7Article in journal (Refereed)
    Abstract [en]

    The one-dimensional Kondo lattice model is studied by means of the numerical diagonalization method. By using massively parallel computations, we were able to study lattices large enough to obtain convergent results for electron densities n <= 2/3. For such densities, an additional ferromagnetic region is found inside the paramagnetic phase. Also, a region is found where the localized spins participate in the low-energy dynamics together with the conduction electrons, thus resulting in a large Fermi surface. These results are an independent confirmation of previous density matrix renormalization group results.

  • 63.
    Bauer, F.
    et al.
    Physik-Department, Technische Universität München.
    Hällgren, Tomas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Seidl, G.
    Department of Physics, Oklahoma State University.
    Discretized gravity in 6D warped space2007In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 278, no 1-3, p. 32-63Article in journal (Refereed)
    Abstract [en]

    We consider discretized gravity in six dimensions. where the two extra dimensions have been compactified on a hyperbolic disk of constant curvature. We analyze different realizations of lattice gravity on the disk at the level of an effective field theory for massive gravitons. It is shown that the observed strong coupling scale of lattice gravity in discretized five-dimensional flat or warped space can be increased if the latticized fifth dimension is wrapped around a hyperbolic disk that has a non-trivial warp factor. As an application, we also study the generation of naturally small Dirac neutrino masses via a discrete volume suppression mechanism and discuss briefly collider implications of our model.

  • 64. Baussan, E.
    et al.
    Blennow, Mattias
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Bogomilov, M.
    Bouquerel, E.
    Caretta, O.
    Cederkäll, J.
    Christiansen, P.
    Coloma, P.
    Cupial, P.
    Danared, H.
    Davenne, T.
    Densham, C.
    Dracos, M.
    Ekelöf, T.
    Eshraqi, M.
    Fernandez Martinez, E.
    Gaudiot, G.
    Hall-Wilton, R.
    Koutchouk, J. -P
    Lindroos, M.
    Loveridge, P.
    Matev, R.
    McGinnis, D.
    Mezzetto, M.
    Miyamoto, R.
    Mosca, L.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Öhman, H.
    Osswald, F.
    Peggs, S.
    Poussot, P.
    Ruber, R.
    Tang, J. Y.
    Tsenov, R.
    Vankova-Kirilova, G.
    Vassilopoulos, N.
    Wilcox, D.
    Wildner, E.
    Wurtz, J.
    A very intense neutrino super beam experiment for leptonic CP violation discovery based on the European spallation source linac2014In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 885, p. 127-149Article in journal (Refereed)
    Abstract [en]

    Very intense neutrino beams and large neutrino detectors will be needed in order to enable the discovery of CP violation in the leptonic sector. We propose to use the proton linac of the European Spoliation Source currently under construction in Lund, Sweden, to deliver, in parallel with the spoliation neutron production, a very intense, cost effective and high performance neutrino beam. The baseline program for the European Spoliation Source linac is that it will be fully operational at 5 MW average power by 2022, producing 2 GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron production and 14 pulses/s for neutrino production. Furthermore, because of the high current required in the pulsed neutrino horn, the length of the pulses used for neutrino production needs to be compressed to a few mu s with the aid of an accumulator ring. A long baseline experiment using this Super Beam and a megaton underground Water Cherenkov detector located in existing mines 300-600 km from Lund will make it possible to discover leptonic CP violation at 5 sigma significance level in up to 50% of the leptonic Dirac CP-violating phase range. This experiment could also determine the neutrino mass hierarchy at a significance level of more than 3 sigma if this issue will not already have been settled by other experiments by then. The mass hierarchy performance could be increased by combining the neutrino beam results with those obtained from atmospheric neutrinos detected by the same large volume detector. This detector will also be used to measure the proton lifetime, detect cosmological neutrinos and neutrinos from supernova explosions. Results on the sensitivity to leptonic CP violation and the neutrino mass hierarchy are presented.

  • 65.
    Beckert, Janis
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    A numerical study of the sign problem in the Hubbard model using a modified discrete   Hubbard-Stratonovich transformation2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 66.
    Belonoshko, A. B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Ab Initio Study of Water Interaction with a Cu Surface2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 21, p. 16267-16270Article in journal (Refereed)
    Abstract [en]

    We have performed a first principles investigation of water interaction with a Cu surface. The calculated surface energy of a Cu(100) slab is in reasonable agreement with experimental data. The energy of water dissociation is in agreement with experiment. The results of the ab initio calculations are compared to experimental data on hydrogen partial pressure. It is concluded that Cu(OH)(ads) is formed due to a reaction between Cu and anoxic water. The energy of the Cu(100) slab with OH and H adsorbed is lower than the energy of the same slab with an adsorbed water molecule.

  • 67.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Arapan, S.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    An ab initio molecular dynamics study of iron phases at high pressure and temperature2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 48Article in journal (Refereed)
    Abstract [en]

    The crystal structure of iron, the major component of the Earth's inner core (IC), is unknown for the IC high pressure (P; 3.3-3.6 Mbar) and temperature (T; 5000-7000 K). There is mounting evidence that the hexagonal close-packed (hcp) phase of iron, stable at the high P of the IC and a low T, might be unstable under the IC conditions due to the impact of high T and impurities. Experiments at the IC P and T are difficult and do not provide a conclusive answer as regards the iron stability at the pressure of the IC and temperatures close to the iron melting curve. Recent theory provides contradictory results regarding the nature of the stable Fe phase. We investigated the possibility of body-centered cubic (bcc) phase stabilization at the P and T in the vicinity of the Fe melting curve by using ab initio molecular dynamics. Thermodynamic calculations, relying on the model of uncorrelated harmonic oscillators, provide nearly identical free energies within the error bars of our calculations. However, direct simulation of iron crystallization demonstrates that liquid iron freezes in the bcc structure at the P of the IC and T = 6000 K. All attempts to grow the hcp phase from the liquid failed. The mechanism of bcc stabilization is explained. This resolves most of the earlier confusion.

  • 68.
    Belonoshko, Anatoly B.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Equation of state for epsilon-iron at high pressures and temperatures2010In: Condensed Matter Physics, ISSN 1607-324X, E-ISSN 2224-9079, Vol. 13, no 2, p. 23605-23615Article in journal (Refereed)
    Abstract [en]

    The equation of state for hexagonal close packed (hcp or ∈) phase of Fe at high pressure is created by employing molecular dynamics (MD) simulations in conjunction with the embedded atom method based on the full potential linear muffin tin orbital (FPLMTO) method. Comparison between the existing experimental data and our calculations suggests that the obtained equation of state can be reliably used for calculating iron volumetric properties under conditions appropriate for the Earth's core. We demonstrate that some experimental data on iron might be subjected to a systematic error. I suggest a model which describes the temperature dependence of the volume better than the Mie-Grüneisen equation.

  • 69.
    Belonoshko, Anatoly B.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Triple fcc-bcc-liquid point on the Xe phase diagram determined by the N-phase method2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 17Article in journal (Refereed)
    Abstract [en]

    There is a discrepancy between the fcc-bcc phase boundaries in Xe determined by the two-phase and the lambda-integration methods. To resolve this issue, I performed large scale (4x10(6) atoms) molecular-dynamics simulations of fcc and bcc Xe phases embedded in liquid Xe. Such simulations, which I call N-phase method, allows for the hydrostatic freezing or melting and direct competition of the phases under consideration. As a result of these long (over several nanoseconds) simulations, I can place the triple fcc-bcc-liquid point on the melting curve of Xe between temperatures of 3470 and 4000 K. This suggests that certain effects are not taken into account in the previous work. Possible reasons are discussed.

  • 70.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Arapan, Sergiu
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Martonak, R.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    MgO phase diagram from first principles in a wide pressure-temperature range2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 5, p. 054110-1-054110-9Article in journal (Refereed)
    Abstract [en]

    Recent laser-initiated strong shockwave measurements at Livermore provide the opportunity for verification of the MgO phase diagram at extreme pressures and temperatures. This calls for a comprehensive study of the MgO phase diagram. The phase diagram is obtained by ab initio molecular dynamics (two phase and Z method) and phonon-based thermodynamic calculations. Energies and forces are computed from first principles projector augmented wave method. The B1 transforms to B2 phase at about 490 GPa. Melting temperatures of B1 are consistent with the two-phase melting curve (Alfe, 2005). The triple point B1-B2-liquid is located at about 2.4 Mbar and 9000 K. The melting curve of the B2 phase rises rather steeply from the triple point. The Hugoniot is likely to cross the B1-B2 boundary first and then to cross the melting curve of B2, therefore, the melting curve of periclase is not relevant for the Hugoniot. MgO melts between 11.3 and 12.5 thousand K and 4.3 and 5 Mbar along the Hugoniot from the B2 phase. The two-phase melting curves of B1 computed with various semiempirical potentials are remarkably close to each other and are consistent with the B1 first principles melting curve at low pressure. This suggests the MgO melting temperatures to be in the close proximity of this determination. The search for new phases of MgO by first principles metadynamics has not produced unknown phases. Therefore, the suggested discontinuity of the Hugoniot at 170 GPa and 3000 K remains enigmatic.

  • 71.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Bryk, T.
    Rosengren, Anders
    Shear Relaxation in Iron under the Conditions of Earth's Inner Core2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 24, p. 245703-Article in journal (Refereed)
    Abstract [en]

    Large scale molecular dynamics simulations of iron at high pressure and temperature are performed to investigate the physics of shear softening. A solid 16 x 10(6) atoms sample of iron is grown out of the liquid with a small solid immersed in it at the start of simulation. We observe that diffusion in the sheared solid is similar to that in liquid, even though at different time scales. This allows us to describe the time dependence of shear stress in terms of elastic and hydrodynamic relaxation. The elastic response of the sample is close to the elastic response of Earth's inner core. This explains the abnormally low shear modulus in the core. The reason for the low shear modulus is the presence of defects of the crystal structure.

  • 72.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Burakovsky, L.
    Chen, S. P.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Mikhaylushkin, A. S.
    Preston, D. L.
    Simak, S. I.
    Swift, D. C.
    Molybdenum at high pressure and temperature: Melting from another solid phase2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 100, no 13Article in journal (Refereed)
    Abstract [en]

    The Gibbs free energies of bcc and fcc Mo are calculated from first principles in the quasiharmonic approximation in the pressure range from 350 to 850 GPa at room temperatures up to 7500 K. It is found that Mo, stable in the bcc phase at low temperatures, has lower free energy in the fcc structure than in the bcc phase at elevated temperatures. Our density-functional-theory-based molecular dynamics simulations demonstrate that fcc melts at higher than bcc temperatures above 1.5 Mbar. Our calculated melting temperatures and bcc-fcc boundary are consistent with the Mo Hugoniot sound speed measurements. We find that melting occurs at temperatures significantly above the bcc-fcc boundary. This suggests an explanation of the recent diamond anvil cell experiments, which find a phase boundary in the vicinity of our extrapolated bcc-fcc boundary.

  • 73.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Derlet, P. M.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Hellman, O.
    Burakovsky, L.
    Swift, D. C.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation2009In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11Article in journal (Refereed)
    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.

  • 74.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Dorogokupets, P. I.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Saxena, S. K.
    Koci, L.
    Ab initio equation of state for the body-centered-cubic phase of iron at high pressure and temperature2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 10Article in journal (Refereed)
    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.

  • 75.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Isaev, E. I.
    Skorodumova, N. V.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Stability of the body-centered-tetragonal phase of Fe at high pressure: Ground-state energies, phonon spectra, and molecular dynamics simulations2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 21Article in journal (Refereed)
    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.

  • 76.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Lukinov, Timofei
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Burakovsky, Leonid
    Preston, Dean L.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Melting of a polycrystalline material2013In: The European Physical Journal Special Topics, ISSN 1951-6355, E-ISSN 1951-6401, Vol. 216, no 1, p. 199-204Article in journal (Refereed)
    Abstract [en]

    Calculating the melting temperature of a solid with a known model of interaction between atoms is nowadays a comparatively simple task. However, when one simulates a single crystal by molecular dynamics method, it does not normally melt at the melting temperature. Instead, one has to significantly overheat it. Yet, a real material melts at the melting point. Here we investigate the impact of the defects and the grain boundaries on melting. We demonstrate that defects and grain boundaries have similar impact and make it possible to simulate melting in close vicinity of thermodynamic melting temperature. We also show that the Z method might be non-applicable in discriminating a stable submelting phase.

  • 77.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Lukinov, Timofei
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Fu, Jie
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Zhao, Jijun
    Davis, Sergio
    Simak, Sergei I.
    Stabilization of body-centred cubic iron under inner-core conditions2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 4, p. 312-+Article in journal (Refereed)
    Abstract [en]

    The Earth's solid core is mostly composed of iron. However, despite being central to our understanding of core properties, the stable phase of iron under inner-core conditions remains uncertain. The two leading candidates are hexagonal close-packed and body-centred cubic (bcc) crystal structures, but the dynamic and thermodynamic stability of bcc iron under inner-core conditions has been challenged. Here we demonstrate the stability of the bcc phase of iron under conditions consistent with the centre of the core using ab initio molecular dynamics simulations. We find that the bcc phase is stabilized at high temperatures by a diffusion mechanism that arises due to the dynamical instability of the phase at lower temperatures. On the basis of our simulations, we reinterpret experimental data as support for the stability of bcc iron under inner-core conditions. We suggest that the diffusion of iron atoms in solid state may explain both the anisotropy and the low shear modulus of the inner core.

  • 78.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Lukinov, Timofiy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. AlbaNova University Center, Sweden.
    Bryk, Taras
    Litasov, Konstantin D.
    Synthesis of heavy hydrocarbons at the core-mantle boundary2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 18382Article in journal (Refereed)
    Abstract [en]

    The synthesis of complex organic molecules with C-C bonds is possible under conditions of reduced activity of oxygen. We have found performing ab initio molecular dynamics simulations of the C-O-H- Fe system that such conditions exist at the core-mantle boundary (CMB). H2O and CO2 delivered to the CMB by subducting slabs provide a source for hydrogen and carbon. The mixture of H2O and CO2 subjected to high pressure (130 GPa) and temperature (4000 to 4500 K) does not lead to synthesis of complex hydrocarbons. However, when Fe is added to the system, C-C bonds emerge. It means that oil might be a more abundant mineral than previously thought.

  • 79.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Ramzan, Muhammad
    Mao, Ho-kwang
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Atomic Diffusion in Solid Molecular Hydrogen2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 2340-Article in journal (Refereed)
    Abstract [en]

    We performed ab initio molecular dynamics simulations of the C2c and Cmca-12 phases of hydrogen at pressures from 210 to 350 GPa. These phases were predicted to be stable at 0 K and pressures above 200 GPa. However, systematic studies of temperature impact on properties of these phases have not been performed so far. Filling this gap, we observed that on temperature increase diffusion sets in the Cmca-12 phase, being absent in C2c. We explored the mechanism of diffusion and computed melting curve of hydrogen at extreme pressures. The results suggest that the recent experiments claiming conductive hydrogen at the pressure around 260 GPa and ambient temperature might be explained by the diffusion. The diffusion might also be the reason for the difference in Raman spectra obtained in recent experiments.

  • 80.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    A possible mechanism of copper corrosion in anoxic water2012In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 92, no 36, p. 4618-4627Article in journal (Refereed)
    Abstract [en]

    Recent experiments show that solid Cu reacts with anoxic water. The reaction is observed by measuring the hydrogen release. This release is continuous and stable over a period of months. We have since theoretically found that water adsorbs dissociatively at a copper surface. But this adsorption is not enough to explain the amount of hydrogen released in the experiment. This observation calls for the explanation of the removal of the reaction product from the surface to provide a clean Cu surface where the water dissociation takes place. In this paper we investigate, by first-principles calculations, two possible mechanisms for this removal: first the possibility of Cu-O-H nanoparticulate formation, and second the diffusion of the dissociation products into Cu. We show that while the formation of nanoparticulates is energetically unfavorable, the diffusion of OH along grain boundaries can be substantial. The OH being placed in a grain boundary of the Cu sample quickly dissociates and O and H atoms diffuse independently of each other. Such a diffusion is markedly larger than the diffusion in bulk Cu. Thus, grain boundary diffusion is a viable mechanism for providing a clean Cu surface for the dissociation of water at the Cu surface. An order-of-magnitude estimate of the amount of hydrogen released in this case agrees with experiment. But this mechanism is not enough to explain the result of the experiment. We propose the formation of nanocrystals of copper oxide as a second step. A decisive experiment is proposed. 

  • 81.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    High-pressure melting curve of platinum from ab initio Z method2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 17, p. 174104-Article in journal (Refereed)
    Abstract [en]

    Pt is widely used as a standard in high-pressure high-temperature experiments. The available experimental and theoretical data on Pt thermal stability is not consistent. We address the issue of high-pressure Pt melting by ab initio molecular dynamics. We demonstrate a remarkable consistency of our computed melting curve with the experimental data by N. R. Mitra, D. L. Decker, and H. B. Vanfleet [Phys. Rev. 161, 613 (1967)]. The extrapolation of their data, based on the Simon equation, nearly coincides with our ab initio computed melting curve. We propose the Pt melting curve in the form P-m(kbar) = 443.0[(T/T-m)(1.14) - 1].

  • 82.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Burakovsky, Leonid
    Preston, Dean L.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Melting of Fe and Fe0.9375Si0.0625 at Earth's core pressures studied using ab initio molecular dynamics2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 22Article in journal (Refereed)
    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.

  • 83.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Hultquist, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.
    Thermal regimes of passivative oxide film formation on Al surface: Theoretical and experimental study2006In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, no 20, p. 4796-4800Article in journal (Refereed)
    Abstract [en]

    We report results of ab initio molecular dynamics simulations of an Al surface exposed to an oxygen atmosphere. The results, supported by experiments performed in this study, demonstrate that the Al surface, by reacting with the oxygen molecules, can be heated above melting temperature and transformed into a liquid. This process is potentially capable of creating an amorphous corrosion scale which might possess an enhanced resistance to deterioration.

  • 84.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, N. V.
    Bastea, S.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Shock wave propagation in dissociating low-Z liquids: D-22005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 12Article in journal (Refereed)
    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.

  • 85.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, N. V.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Burakovsky, L.
    Preston, D. L.
    High-pressure melting of MgSiO32005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 19Article in journal (Refereed)
    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.

  • 86.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, N. V.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Melting and critical superheating2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 1Article in journal (Refereed)
    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.

  • 87.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, Natalia V.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic anisotropy of Earth's inner core2008In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 319, no 5864, p. 797-800Article in journal (Refereed)
    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.

  • 88.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Davis, Sergio
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Department of Physics, Uppsala University.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Simak, Sergei
    Burakovsky, Leonid
    Preston, D. L.
    Xenon melting: Density functional theory versus diamond anvil cell experiments2006In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 74, p. 054114-Article in journal (Refereed)
    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.

  • 89.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Davis, Sergio
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skorodumova, Natalia
    Department of Physics, Uppsala University.
    Lundow, Per-Håkan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Properties of the fcc Lennard-Jones crystal model at the limit of superheating2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 76, p. 064121-Article in journal (Refereed)
    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.

  • 90.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Koči, L.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Stability of the bcc phase of 4He close to the melting curve: A molecular dynamics study2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 1, p. 012503-Article in journal (Refereed)
    Abstract [en]

    We have investigated whether the Aziz et al. [J. Chem. Phys. 70, 4330 (1979)] model for (4)He renders the body-centered cubic phase more stable than the face-centered cubic phase in the proximity of the melting curve. Using molecular dynamics, we have simulated these solid phases in equilibrium with the liquid at a number of densities. In contrast to previous free energy molecular dynamics calculations, the model stabilizes the body-centered cubic phase. The stability field is just 5 degrees. wide below the melting curve at pressures around 140 Kbar and about 70 degrees wide at pressures around 750 Kbar. Considering that the body-centered cubic phase is dynamically unstable at low temperature, this result bears striking similarities to transition metal phase diagrams.

  • 91.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Lukinov, Tymofiy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Zhao, Jijun
    Dalian University of Technology, China.
    Fu, Jie
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Davis, Sergio
    Simak, Sergei
    Mechanism of the body-centered cubic iron stabilization under the Earth core conditionsManuscript (preprint) (Other academic)
  • 92.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Iron shear modulus in the Earth's inner core2010In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, no 12, p. A75-A75Article in journal (Other academic)
  • 93.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Skorodumova, Natalia
    Department of Physics, Uppsala University.
    Davis, Sergio
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Osiptsov, Alexander
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Origin of the Low Rigidity of the Earth's Inner Core2007In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, p. 1603-Article in journal (Refereed)
    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.

  • 94. Benazzouz, Brahim K.
    et al.
    Zaoui, Ali
    Belonoshko, Anatoly B.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Determination of the melting temperature of kaolinite by means of the Z-method2013In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 98, no 10, p. 1881-1885Article in journal (Refereed)
    Abstract [en]

    The melting temperature of materials is an important thermodynamic property. Despite the importance of kaolinite, one of the most common clay minerals on the Earth's surface, its thermal and melting behavior is poorly understood. We apply here the Z-method to determine the melting temperature (T-m) and the limit of superheating (T-LS) of kaolinite. The T-m is found at 1818 K (8.85 GPa), and T-LS at 1971 K (6.8 GPa). The diffusion coefficient for all atoms has been calculated in a broad temperature range. The calculated characteristics and, in particular, their dependence on temperature have confirmed the solid-liquid transition and strongly support the calculated melting point. In addition, some computed quantities, such as the radial distribution function, coordination numbers and mean-square displacement, were used to confirm the liquid state of kaolinite from the melting temperature as well as at other temperatures in the liquid branch. The diffusion coefficient for different atoms has been calculated throughout the isochore. These quantities and in particular their evolution under temperature have confirmed the solid-liquid states of kaolinite and the presence of the melting point. The latter quantity constitutes the first ever melting simulation of a clay mineral with close agreement to the experimental one.

  • 95.
    Benites, Mario
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Covariant Prescription of Holographic Entanglement Entropy in AdS3 and BTZ Black Hole2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 96.
    Bergdahl, Joakim
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Almgren, Lars
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Quantitative Analysis of Physical and Statistical Properties of Flocks.2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Flocking behavior is a common phenomenon in nature in the form of, for instance, flocks

    of birds or schools of fish. Making the assumption that the members of a flock can be

    considered a system of interacting particles it is possible to use methods from statistical

    physics to quantitatively analyze flocks and their properties. This way, a flock can exist in

    various thermodynamic phases and exhibit phase transitions depending on changes within

    the flock. In this report the flock analysis is performed with the help of a model originally

    created by Vicsek et al. The model is governed by certain parameters controlling the

    interaction between individual flock members. From the results it is possible to see that

    even small deviations in these parameter values can lead to great phase alterations as well

    as phase transitions, which strengthens to the assumption that a flock can be considered

    a system of particles.

  • 97.
    Bergh, Cathrine
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Modeling of Conformational Transitions in Membrane Proteins with Coarse-Grained Methods2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Understanding the dynamics of proteins is crucial in order to understand life on a molecular level. In this Bachelor’s thesis large scale motions of the membrane protein SERCA has been investigated with coarse-grained methods. The goal was to find certain places in the structure where mutations could alter and affect the functionality of the protein, possibly leading to disease. The protein was modeled with an elastic network model and simulated with Langevin dynamics. Data from the simulations was used to calculate all the places were formation of stabilizing salt bridges were possible and these were then compared with mutations found in real cancerous cells. Promising results were obtained but need to be investigated further with more sophisticated methods before any conclusions can be drawn regarding their significance for the protein functionality. Likewise, the use of elastic network models together with Langevin dynamics showed to be a good alternative to sample large conformational changes in proteins.

  • 98.
    Bergkvist, Sara
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    McCulloch, Ian
    KTH.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Spinful bosons in an optical lattice2006In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, no 5, p. 053419-1-053419-8Article in journal (Refereed)
    Abstract [en]

    We analyze the behavior of cold spin-1 particles with antiferromagnetic interactions in a one-dimensional optical lattice using density matrix renormalization group calculations. Correlation functions and the dimerization are shown and we also present results for the energy gap between ground state and the spin excited states. We confirm the anticipated phase diagram, with Mott-insulating regions of alternating dimerized S=1 chains for odd particle density versus on-site singlets for even density. We find no evidence for any additional ordered phases in the physically accessible region, however for sufficiently large spin interaction, on-site singlet pairs dominate leading, for odd density, to a breakdown of the Mott insulator or, for even density, a real-space singlet superfluid.

  • 99.
    Bergkvist, Sara
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Saers, Robert
    Umeå Univ, Dept Phys.
    Lundh, Emil
    Umeå Univ, Dept Phys.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rehn, Magnus
    Umeå Univ, Dept Phys.
    Kastberg, Anders
    Umeå Univ, Dept Phys.
    Transition from a two-dimensional superfluid to a one-dimensional mott insulator2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 11, p. 110401-1-110401-5Article in journal (Refereed)
    Abstract [en]

    A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed.

  • 100.
    Bergkvist Sylvan, Sara
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Numerical studies of spin chains and cold atoms in optical lattices2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    An important, but also difficult, research field in condensed matter physics is that of strongly correlated systems. This thesis considers two topics in this field.

    The first topic is disorder and frustration in spin models. The introduction of disorder into quantum spin chains creates a complex problem. The ground state of the random-bond spin-1 Heisenberg chain is studied by means of stochastic series expansion quantum Monte Carlo simulation, applying the concept of directed loops. It is found that this system undergoes a phase transition to the random-singlet phase if the bond disorder is strong enough. Further a frustrated spin system is investigated. The frustration is introduced by having spins positioned on a triangular lattice. Performing a quantum Monte Carlo simulation for such a frustrated lattice leads to the occurrence of the infamous sign problem. This problem is investigated and it is shown that it is possible to use a meron cluster approach to reduce its effect for some specific models.

    The second topic concerns atomic condensates in optical lattices. A system of trapped bosonic atoms in such a lattice is described by a Bose-Hubbard model with an external confining potential. Using quantum Monte Carlo simulations it is demonstrated that the local density approximation that relates the observables of the unconfined and the confined models yields quantitatively correct results in most of the interesting parameter range of the model. Further, the same model with the addition that the atoms carry spin-1 is analyzed using density matrix renormalization group calculations. The anticipated phase diagram, with Mott insulating regions of dimerized spin-1 chains for odd particle density, and on-site singlets for even density is confirmed. Also an ultracold gas of bosonic atoms in an anisotropic two dimensional optical lattice is studied. It is found that if the system is finite in one direction it exhibits a quantum phase transition. The Monte Carlo simulations performed show that the transition is of Kosterlitz-Thouless type.

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