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  • 1. Basylko, S. A.
    et al.
    Kundrotas, P. J.
    Onischouk, V. A.
    Tornau, E. E.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Coulomb gap in a model with finite charge-transfer energy2001Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6302, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Coulomb gap in a donor-acceptor model with finite charge-transfer energy Delta describing the electronic system on the dielectric side of the metal-insulator transition is investigated by means of computer simulations on two- and three-dimensional finite samples with a random distribution of equal amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry of the model presented with respect to the exchange of donors and accepters are derived. In the immediate neighborhood of the Fermi energy mu. the single-particle density of states g(epsilon) is determined solely by finite size effects, and g(epsilon) further away from mu is described by an asymmetric power law with a nonuniversal exponent, depending on the parameter Delta.

  • 2. Basylko, S. A.
    et al.
    Lundow, Per Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    One-dimensional Kondo lattice model studied through numerical diagonalization2008Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 7Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3. Basylko, S. A.
    et al.
    Onischouk, V. A.
    Kundrotas, P. J.
    Tornau, E. E.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Ground-state study of a donor-acceptor model with finite charge-transfer energy2000Inngår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 271, nr 02-jan, s. 134-138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A donor-acceptor model with randomly distributed N donor and N acceptor sites and with finite charge transfer energy Delta is investigated at zero temperature by means of computer simulations on two-dimensional samples of different sizes, We demonstrate that the density of one-electron excitations g(epsilon) for accepters in the vicinity of the Fermi energy mu depends essentially on the size of the sample investigated and that g(epsilon) further away from mu exhibits a size-independent power-law with the non-universal exponent decreasing with increasing Delta. Rigorous relations for mu and for the mapping of g(epsilon) for donors into g(epsilon) for accepters are also given.

  • 4.
    Basylko, S. A.
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Onischouk, V. A.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    ac conductivity of a Coulomb glass from computer simulations2004Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 2, s. 024201-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method for calculating the photon-induced hopping ac conductivity of a Coulomb glass by computer simulation is proposed. Results obtained by using an effective relaxation algorithm for two three-dimensional models of a Coulomb glass are reported. ac conductance data clearly demonstrate the transition from super-linear to a sub-quadratic power law. We argue that the same qualitative behavior should be expected for compensated semiconductors. It is shown that the transition is driven by the Coulomb energy of sites forming resonant pairs and not by the width of the Coulomb gap.

  • 5. Basylko, S. A.
    et al.
    Onischouk, V. A.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Coulomb glass in the random phase approximation2002Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A three-dimensional model of the electrons localized on randomly distributed donor sites of density n and with the acceptor charge uniformly smeared on these sites, -Ke on each, is considered in the random phase approximation (RPA). For the case K = 1/2 the free energy, the density of the one-site energies (DOSE) epsilon, and the pair OSE correlators are found. In the high-temperature region (e(2) n(1/3)/T) < 1 (T is the temperature) RPA energies and DOSE are in a good agreement with the corresponding data of Monte Carlo simulations. Thermodynamics of the model in this region is similar to the one of an electrolyte in the regime of Debye screening. In the vicinity of the Fermi level μ = 0 the OSE correlations, depending on sgn(ε(1) . ε(2)) and with very slow decoupling law, have been found. The main result is that even in the temperature range where the energy of a Coulomb glass is determined by Debye screening effects, the correlations of the long-range nature between the OSE still exist.

  • 6. Basylko, S. A.
    et al.
    Onischouk, V. A.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Coulomb glass in the restricted random phase approximation2002Inngår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 298, nr 06-maj, s. 416-421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A three-dimensional model of N/2 electrons localized on N randomly distributed donor sites of density n and with the acceptor charge uniformly smeared on these sites, -e/2 on each. has been considered in the restricted random phase approximation (RRPA) which uses the set of 3N Fourier components of the local charge density as the independent collective variables. The energy e(T) per site and the density of one-site excitation energy (DOSE) g(epsilon) are shown to he, respectively, in excellent quantitative and in good qualitative agreement with the Monte Carlo simulation data in the whole temperature region 0.1 < T < 100, where these simulations were performed (e(2)n(1/3)/k(B) being the temperature scale). The pair correlator for the one-site energies g(epsilon,+/-epsilon, r) is found to have the slow decoupling law similar to(+/-1/r) for T less than or similar to 1 and r much greater than r(d) (r(d), Debye screening radius). The status of the commonly accepted asymptotic g(epsilon) similar to (epsilon - mu)(d-1) (d and mu being, respectively, the spatial dimension and the Fermi energy) is discussed. The deduction of this asymptotic is shown to be based on the strong and questionable conjecture about decoupling of correlations between one-site excitation energies in the vicinity of mu.

  • 7.
    Belonoshko, A. B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori. KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori. KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Ab Initio Study of Water Interaction with a Cu Surface2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 21, s. 16267-16270Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Arapan, S.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    An ab initio molecular dynamics study of iron phases at high pressure and temperature2011Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, nr 48Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 9.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Arapan, Sergiu
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Martonak, R.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    MgO phase diagram from first principles in a wide pressure-temperature range2010Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 5, s. 054110-1-054110-9Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 10.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Bryk, T.
    Rosengren, Anders
    Shear Relaxation in Iron under the Conditions of Earth's Inner Core2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, nr 24, s. 245703-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 11.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Lukinov, Timofei
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Burakovsky, Leonid
    Preston, Dean L.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Melting of a polycrystalline material2013Inngår i: The European Physical Journal Special Topics, ISSN 1951-6355, E-ISSN 1951-6401, Vol. 216, nr 1, s. 199-204Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 12.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Lukinov, Timofiy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori. KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. AlbaNova University Center, Sweden.
    Bryk, Taras
    Litasov, Konstantin D.
    Synthesis of heavy hydrocarbons at the core-mantle boundary2015Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikkel-id 18382Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 13.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    A possible mechanism of copper corrosion in anoxic water2012Inngår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 92, nr 36, s. 4618-4627Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 14.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    High-pressure melting curve of platinum from ab initio Z method2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 17, s. 174104-Artikkel i tidsskrift (Fagfellevurdert)
    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].

  • 15.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Burakovsky, Leonid
    Preston, Dean L.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Melting of Fe and Fe0.9375Si0.0625 at Earth's core pressures studied using ab initio molecular dynamics2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 22Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 16.
    Belonoshko, Anatoly B.
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Dong, Qian
    KTH, Tidigare Institutioner, Materialvetenskap.
    Hultquist, Gunnar
    KTH, Tidigare Institutioner, Materialvetenskap.
    Leygraf, Christofer
    KTH, Tidigare Institutioner, Materialvetenskap.
    First-principles study of hydrogen diffusion in alpha-Al2O3 and liquid alumina2004Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the energetics and mobility of neutral hydrogen in alumina Al2O3 using ab initio density-functional calculations. The mobility of hydrogen was studied in corundum (alpha-Al2O3) as well as in liquid alumina. Using both static as well as molecular-dynamics calculations, and applying classical transition state theory, we derive the temperature-dependent diffusivity of hydrogen in alpha-Al2O3 as D(T)=(21.7x10(-8) m(2)/s)exp(-1.24 eV/kT). The corresponding diffusivity of hydrogen in liquid/amorphous alumina, derived directly from ab initio molecular dynamics calculations, is D(T)=(8.71x10(-7) m(2)/s)exp(-0.91 eV/kT). The computed diffusivity compares very well to experimental data. We conclude that diffusion of neutral hydrogen through the bulk of alumina is a good approximation of the mechanism for hydrogen mobility in corrosion scales. The representation of grain-boundary structures by amorphous alumina is, probably, realistic at higher temperatures.

  • 17.
    Belonoshko, Anatoly B.
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Dong, Qian
    KTH, Tidigare Institutioner, Materialvetenskap.
    Hultquist, Gunnar
    KTH, Tidigare Institutioner, Materialvetenskap.
    Leygraf, Christofer
    KTH, Tidigare Institutioner, Materialvetenskap.
    First-principles study of hydrogen diffusion in α-Al 2O3 and liquid alumina2004Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 69, nr 2, s. 243021-243026Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the energetics and mobility of neutral hydrogen in alumina Al2O3 using ab initio density-functional calculations. The mobility of hydrogen was studied in corundum (α-Al2O 3) as well as in liquid alumina. Using both static as well as molecular-dynamics calculations, and applying classical transition state theory, we derive the temperature-dependent diffusivity of hydrogen in α-Al 2O3 as D(T)=(21.7 × 10-8 m 2/s)exp(-1.24 eV/kT). The corresponding diffusivity of hydrogen in liquid/amorphous alumina, derived directly from ab initio molecular dynamics calculations, is D(T)=(8.71 × 10-7 m2/s)exp(-0.91 eV/kT). The computed diffusivity compares very well to experimental data. We conclude that diffusion of neutral hydrogen through the bulk of alumina is a good approximation of the mechanism for hydrogen mobility in corrosion scales. The representation of grain-boundary structures by amorphous alumina is, probably, realistic at higher temperatures.

  • 18.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Hultquist, Gunnar
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    Thermal regimes of passivative oxide film formation on Al surface: Theoretical and experimental study2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 20, s. 4796-4800Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 19.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, N. V.
    Bastea, S.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Shock wave propagation in dissociating low-Z liquids: D-22005Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, nr 12Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 20.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, N. V.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Burakovsky, L.
    Preston, D. L.
    High-pressure melting of MgSiO32005Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, nr 19Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 21.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, N. V.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Melting and critical superheating2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 22.
    Belonoshko, Anatoly B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, Natalia V.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic anisotropy of Earth's inner core2008Inngår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 319, nr 5864, s. 797-800Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 23.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Davis, Sergio
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Ahuja, Rajeev
    Department of Physics, Uppsala University.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Simak, Sergei
    Burakovsky, Leonid
    Preston, D. L.
    Xenon melting: Density functional theory versus diamond anvil cell experiments2006Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 74, s. 054114-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 24.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Davis, Sergio
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Skorodumova, Natalia
    Department of Physics, Uppsala University.
    Lundow, Per-Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Properties of the fcc Lennard-Jones crystal model at the limit of superheating2007Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 76, s. 064121-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 25.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Koči, L.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Stability of the bcc phase of 4He close to the melting curve: A molecular dynamics study2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 1, s. 012503-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 26.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Iron shear modulus in the Earth's inner core2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 12, s. A75-A75Artikkel i tidsskrift (Annet vitenskapelig)
  • 27.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Skorodumova, Natalia
    Department of Physics, Uppsala University.
    Davis, Sergio
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Osiptsov, Alexander
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Origin of the Low Rigidity of the Earth's Inner Core2007Inngår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, s. 1603-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 28.
    Bergkvist, Sara
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Henelius, Patrik
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Ground state of the random-bond spin-1 Heisenberg chain2002Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 66, s. 134407-1-134407-9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stochastic series expansion quantum Monte Carlo is used to study the ground state of the antiferromagnetic spin-1 Heisenberg chain with bond disorder. Typical spin- and string-correlation functions behave in accordance with real-space renormalization group predictions for the random-singlet phase. The average string-correlation function decays algebraically with an exponent of -0.378(6), in very good agreement with the prediction of -(3-root5)/2similar or equal to-0.382, while the average spin-correlation function is found to decay with an exponent of about -1, quite different from the expected value of -2. By implementing the concept of directed loops for the spin-1 chain we show that autocorrelation times can be reduced by up to two orders of magnitude.

  • 29.
    Bergkvist, Sara
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Henelius, Patrik
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Local-density approximation for confined bosons in an optical lattice2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, s. 053601-1-053601-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate local and global properties of the one-dimensional Bose-Hubbard model with an external confining potential, describing an atomic condensate in an optical lattice. Using quantum Monte Carlo techniques we demonstrate that a local-density approximation, which relates the unconfined and the confined model, yields quantitatively correct results in most of the interesting parameter range. We also examine claims of universal behavior in the confined system, and demonstrate the origin of a previously calculated fine structure in the experimentally accessible momentum distribution.

  • 30.
    Bergkvist, Sara
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Henelius, Patrik
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Reduction of the sign problem using the meron-cluster approach2003Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 68, s. 016122-1-016122-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sign problem in quantum Monte Carlo calculations is analyzed using the meron-cluster solution. A meron is a loop that alters the sign of the configuration, and the concept of merons can be used to solve the sign problem for a limited class of models. Here we show that the method can be used to reduce the sign problem in a wider class of models. We investigate how the meron solution evolves between a point in parameter space where it eliminates the sign problem and a point where it does not affect the sign problem at all. In this intermediate regime, the merons can be used to reduce the sign problem. The average sign still decreases exponentially with system size and inverse temperature, but with a different prefactor. The sign exhibits the slowest decrease in the vicinity of points where the meron-cluster solution eliminates the sign problem. We have used stochastic series expansion quantum Monte Carlo combined with the concept of directed loops.

  • 31.
    Bergkvist, Sara
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    McCulloch, Ian
    KTH.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Spinful bosons in an optical lattice2006Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, nr 5, s. 053419-1-053419-8Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 32.
    Bergkvist, Sara
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Saers, Robert
    Umeå Univ, Dept Phys.
    Lundh, Emil
    Umeå Univ, Dept Phys.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rehn, Magnus
    Umeå Univ, Dept Phys.
    Kastberg, Anders
    Umeå Univ, Dept Phys.
    Transition from a two-dimensional superfluid to a one-dimensional mott insulator2007Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, nr 11, s. 110401-1-110401-5Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 33. Bowen, A.
    et al.
    Gulacsi, M.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Finite temperature correlation functions of one-dimensional interacting electron systems2000Inngår i: Australian journal of physics (Print), ISSN 0004-9506, E-ISSN 1446-5582, Vol. 53, nr 4, s. 553-566Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The well-known bosonisation method of one-dimensional electron systems is extended to finite temperatures. As an example, the correlation functions of the non-interacting case are explicitly calculated. The presentation is pedagogical and is intended to be accessible to graduate students or physicists who are not experts in this field.

  • 34. Burakovsky, L.
    et al.
    Chen, S. P.
    Preston, D. L.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Moriarty, J. A.
    High-Pressure-High-Temperature Polymorphism in Ta: Resolving an Ongoing Experimental Controversy2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, nr 25, s. 255702-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phase diagrams of refractory metals remain essentially unknown. Moreover, there is an ongoing controversy over the high-pressure melting temperatures of these metals: results of diamond anvil cell (DAC) and shock wave experiments differ by at least a factor of 2. From an extensive ab initio study on tantalum we discovered that the body-centered cubic phase, its physical phase at ambient conditions, transforms to another solid phase, possibly hexagonal omega phase, at high temperature. Hence the sample motion observed in DAC experiments is very likely not due to melting but internal stresses accompanying a solid-solid transformation, and thermal stresses associated with laser heating.

  • 35.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Model for diffusion at the microcanonical superheating limit from atomistic computer simulations2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 6, s. 064102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 36.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    An atomistic model for homogeneous meltingManuskript (Annet vitenskapelig)
    Abstract [en]

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

  • 37.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    van Duin, Adri
    Johansson, Börje
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Molecular dynamics simulation of zirconia melting2010Inngår i: Central European Journal of Physics, ISSN 1895-1082, E-ISSN 1644-3608, Vol. 8, nr 5, s. 789-797Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 38. Gulacsi, M.
    et al.
    McCulloch, I. P.
    Juozapavicius, Ausrius
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Magnetism in the dilute Kondo lattice model2004Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, nr 17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The one-dimensional dilute Kondo lattice model is investigated by means of bosonization for different dilution patterns of the array of impurity spins. The physical picture is very different if a commensurate or incommensurate doping of the impurity spins is considered. For the commensurate case, the obtained phase diagram is vertified using a non-Abelian density-matrix renormalization-group algorithm. The paramagnetic phase widens at the expense of the ferromagnetic phase as the f spins are diluted. For the incommensurate case, short-range antiferromagnetic correlations are found to dominate at low doping, which distinguishes the dilute Kondo lattice model from the standard Kondo lattice model.

  • 39. Haggkvist, R.
    et al.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Andren, D.
    Kundrotas, Petras
    KTH, Tidigare Institutioner, Fysik.
    Lundow, Per Håkan
    KTH, Tidigare Institutioner, Fysik.
    Markstrom, K.
    Computation of the Ising partition function for two-dimensional square grids2004Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 69, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An improved method for obtaining the Ising partition function of nxn square grids with periodic boundary is presented. Our method applies results from Galois theory in order to split the computation into smaller parts and at the same time avoid the use of numerics. Using this method we have computed the exact partition function for the (320x320) grid, the (256x256) grid, and the (160x160) grid, as well as for a number of smaller grids. We obtain scaling parameters and compare with what theory prescribes.

  • 40. Haggkvist, R.
    et al.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Lundow, Per Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Markstrom, K.
    Andren, D.
    Kundrotas, P.
    On the Ising model for the simple cubic lattice2007Inngår i: Advances in Physics, ISSN 0001-8732, E-ISSN 1460-6976, Vol. 56, nr 5, s. 653-755Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The Ising model was introduced in 1920 to describe a uniaxial system of magnetic moments, localized on a lattice, interacting via nearest-neighbour exchange interaction. It is the generic model for a continuous phase transition and arguably the most studied model in theoretical physics. Since it was solved for a two-dimensional lattice by Onsager in 1944, thereby representing one of the very few exactly solvable models in dimensions higher than one, it has served as a testing ground for new developments in analytic treatment and numerical algorithms. Only series expansions and numerical approaches, such as Monte Carlo simulations, are available in three dimensions. This review focuses on Monte Carlo simulation. We build upon a data set of unprecedented size. A great number of quantities of the model are estimated near the critical coupling. We present both a conventional analysis and an analysis in terms of a Puiseux series for the critical exponents. The former gives distinct values of the high- and low-temperature exponents; by means of the latter we can get these exponents to be equal at the cost of having true asymptotic behaviour being found only extremely close to the critical point. The consequences of this for simulations of lattice systems are discussed at length.

  • 41.
    Hultquist, Gunnar
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Graham, M. J.
    Szakalos, P.
    Sproule, G. I.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Gråsjö, L..
    Hydrogen gas production during corrosion of copper by water2011Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 53, nr 1, s. 310-319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper considers the corrosion of copper in water by (1) short term open system weight measurements and (2) long term closed system immersion in distilled water (13 800 h) without O-2 at 21-55 degrees C In the latter experiments the hydrogen gas pressure is measured above the immersed copper and approaches similar to 10(-3) bar at equilibrium This pressure is mostly due to copper corrosion and greatly exceeds that in ambient air Accordingly this measured hydrogen pressure from copper corrosion increases with temperature and has the same dependency as the concentration of OH- in the ion product [OH-] [H+].

  • 42.
    Hultquist, Gunnar
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    Szakalos, P.
    Graham, M. J.
    Belonoshko, A. B.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Reply to Lars O. Werme et al.: "Comments on 'Water Corrodes Copper'"2010Inngår i: Catalysis Letters, ISSN 1011-372X, E-ISSN 1572-879X, Vol. 135, nr 3-4, s. 167-168Artikkel i tidsskrift (Fagfellevurdert)
  • 43.
    Hultquist, Gunnar
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Szakalos, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Graham, M. J.
    Belonoshko, Antoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Sproule, G. I.
    Grasjo, L.
    Dorogokupets, P.
    Danilov, B.
    Aastrup, T.
    Wikmark, G.
    Chuah, G. K.
    Eriksson, Jan Christer
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Water Corrodes Copper2009Inngår i: Catalysis Letters, ISSN 1011-372X, E-ISSN 1572-879X, Vol. 132, nr 3-4, s. 311-316Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    According to a current concept, copper canisters of thickness 0.05 m will be safe for nuclear waste containment for 100,000 years. We show that more than 1 m copper thickness might be required for 100,000 years durability based on water exposures of copper for 20 h, 7 weeks, 15 years, and 333 years. An observed evolution of hydrogen which involves heterogeneous catalysis of molecular hydrogen, first principles simulations, thermodynamic considerations and corrosion product characterization provide further evidence that water corrodes copper resulting in the formation of a copper hydroxide. These findings cast additional doubt on copper for nuclear waste containment and other important applications.

  • 44. Häggkvist, R.
    et al.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Andrén, D.
    Kundrotas, Petras
    KTH, Tidigare Institutioner, Fysik.
    Lundow, Per Håkan
    KTH, Tidigare Institutioner, Fysik.
    Markström, K.
    A Monte Carlo sampling scheme for the Ising model2004Inngår i: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 114, nr 02-jan, s. 455-480Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we describe a Monte Carlo sampling scheme for the Ising model and similar discrete-state models. The scheme does not involve any particular method of state generation but rather focuses on a new way of measuring and using the Monte Carlo data. We show how to reconstruct the entropy S of the model, from which, e.g., the free energy can be obtained. Furthermore we discuss how this scheme allows us to more or less completely remove the effects of critical fluctuations near the critical temperature and likewise how it reduces critical slowing down. This makes it possible to use simple state generation methods like the Metropolis algorithm also for large lattices.

  • 45. Juozapavicius, A.
    et al.
    McCulloch, I. P.
    Gulacsi, M.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Ferromagnetic phases in the Kondo lattice model2002Inngår i: Philosophical magazine. B. Physics of condensed matter. Electronic, optical and magnetic properties, ISSN 0141-8637, Vol. 82, nr 11, s. 1211-1224Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using an SO (4) invariant density-matrix renormalization group algorithm a sufficient numerical accuracy is achieved to demonstrate new ferromagnetic phase regions inside the paramagnetic area of the one- dimensional antiferromagnetic Kondo lattice model phase diagram. Spin- spin correlation functions, energy gap, number of singlets and other physical properties are investigated in detail. Direct measurements of the magnetization reveal continuous paramagnetic- ferromagnetic phase transitions.

  • 46. Kundrotas, P. J.
    et al.
    Onischouk, V. A.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Coulomb correlation gap: Finite-size analysis2001Inngår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 287, nr 04-mar, s. 278-282Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A semiclassical model with randomly distributed N donor and K x N acceptor sites and with infinite-range Coulomb interaction is investigated by means of computer simulations on two-dimensional samples of different sizes. The shape of the Coulomb correlation gap in the density of one-electron excitations g(epsilon) is obtained for different values of K within a wide energy interval around the Fermi energy mu. Using simple scaling arguments we demonstrate that the true behavior of g(epsilon) in the immediate neighborhood of mu is hidden by the finite-size effects and find that g(epsilon) further away from mu is described by a power-law with an exponent, depending on K and the sign of epsilon - mu.

  • 47. Lapinskas, S.
    et al.
    Tornau, E. E.
    Rosengren, Anders
    KTH, Tidigare Institutioner                               , Fysik.
    Model of cation ordering in A (B-x ' B1-x '')O-3 relaxors2001Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6305, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have shown that the lattice-gas model with four repulsive pair interaction constants (corresponding to the four nearest coordination shells) on a simple cubic lattice is a sufficient model to describe the main types of cation ordering in relaxors. The phase diagram, obtained by the cluster variation method, shows the sequences of transitions between the phases 1:2 -->1:1 --> disordered and 1:2 --> disordered.

  • 48. Lashley, Jason
    et al.
    Riseborough, Peter
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    A tribute to James L. Smith Foreword2009Inngår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, nr 22-24, s. 1751-1756Artikkel i tidsskrift (Fagfellevurdert)
  • 49.
    Lukinov, Tymofiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Impact of crystal lattice defects on crystal melting: A molecular dynamics study2013Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, s. 95-98Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An ideal infinite lattice, when subjected to heating does not melt at the thermodynamic melting temperature. Instead, it remains solid metastably up to considerably higher temperatures. This effect is called superheating. We performed a molecular dynamics simulation of Xenon using Lennard-Jonesium potential with several types of defects. We observed a superheating effect on the chosen model for several pressures and found that the presence of grain inclusion or grain interface eliminates the superheating effect.

  • 50.
    Lukinov, Tymofiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Martonak, Roman
    Metadynamics study of fcc-bcc phase transition in Xenon at high pressure and temperatureManuskript (preprint) (Annet vitenskapelig)
12 1 - 50 of 63
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