Browsing by Subject "ENERGIES"

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  • De Backer, A.; Domain, C.; Becquart, C. S.; Luneville, L.; Simeone, D.; Sand, A. E.; Nordlund, K. (2018)
    The impacts of ions and neutrons in metals cause cascades of atomic collisions that expand and shrink, leaving microstructure defect debris, i.e. interstitial or vacancy clusters or loops of different sizes. In De Backer et al (2016 Europhys. Lett. 115 26001), we described a method to detect the first morphological transition, i.e. the cascade fragmentation in subcascades, and a model of primary damage combining the binary collision approximation and molecular dynamics (MD). In this paper including W, Fe, Be, Zr and 20 other metals, we demonstrate that the fragmentation energy increases with the atomic number and decreases with the atomic density following a unique power law. Above the fragmentation energy, the cascade morphology can be characterized by the cross pair correlation functions of the multitype point pattern formed by the subcascades. We derive the numbers of pairs of subcascades and observed that they follow broken power laws. The energy where the power law breaks indicates the second morphological transition when cascades are formed by branches decorated by chaplets of small subcascades. The subcascade interaction is introduced in our model of primary damage by adding pairwise terms. Using statistics obtained on hundreds of MD cascades in Fe, we demonstrate that the interaction of subcascades increases the proportion of large clusters in the damage created by high energy cascades. Finally, we predict the primary damage of 500 keV Fe ion in Fe and obtain cluster size distributions when large statistics of MD cascades arc not feasible.
  • Lehtola, Susi (2020)
    Knowledge of the repulsive behavior of potential energy curves V (R) at R -> 0 is necessary for understanding and modeling irradiation processes of practical interest. V (R) is in principle straightforward to obtain from electronic structure calculations; however, commonly used numerical approaches for electronic structure calculations break down in the strongly repulsive region due to the closeness of the nuclei. In this work, we show by comparison to fully numerical reference values that a recently developed procedure [S. Lehtola, J. Chem. Phys. 151, 241102 (2019)] can be employed to enable accurate linear combination of atomic orbitals calculations of V (R) even at small R by a study of the seven nuclear reactions He-2 (sic) Be, HeNe (sic) Mg, Ne-2 (sic) Ca, HeAr (sic) Ca, MgAr (sic) Zn, Ar-2 (sic) Kr, and NeCa (sic) Zn.
  • Leverentz, Hannah R.; Siepmann, J. Ilja; Truhlar, Donald G.; Loukonen, Ville; Vehkamäki, Hanna (2013)
  • Antchev, G.; Garcia, F.; Heino, J.; Lauhakangas, R.; Naaranoja, T.; Oljemark, F.; Orava, R.; Österberg, K.; Saarikko, H.; Welti, J.; TOTEM Collaboration (2015)
    The TOTEM experiment has made a precise measurement of the elastic proton proton differential cross-section at the centre-of-mass energy root s = 8 TeV based on a high-statistics data sample obtained with the beta* = 90 m optics. Both the statistical and systematic uncertainties remain below 1%, except for the t-independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027 <vertical bar t vertical bar <0.2 GeV2 with a significance greater than 7 sigma. Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t = 0, and further applying the optical theorem, yields total cross-section estimates of (101.5 +/- 2.1) mb and (101.9 +/- 2.1) mb, respectively, in agreement with previous TOTEM measurements. (C) 2015 The Authors. Published by Elsevier B.V.
  • Kuopanportti, Pekko; Ropo, Matti; Holmberg, Daniel; Levamaki, Henrik; Kokko, Kalevi; Granroth, Sari; Kuronen, Antti (2022)
    To enable accurate molecular dynamics simulations of iron-chromium alloys with surfaces, we develop, based on density-functional-theory (DFT) calculations, a new interatomic Fe-Cr potential in the Tersoff formalism. Contrary to previous potential models, which have been designed for bulk Fe-Cr, we extend our potential fitting database to include not only conventional bulk properties but also surface-segregation energies of Cr in bcc Fe. In terms of reproducing our DFT results for the bulk properties, the new potential is found to be superior to the previously developed Tersoff potential and competitive with the concentration-dependent and two-band embedded-atom-method potentials. For Cr segregation toward the (100) surface of an Fe-Cr alloy, only the new potential agrees with our DFT calculations in predicting preferential segregation of Cr to the topmost surface layer, instead of the second layer preferred by the other potentials. We expect this rectification to foster future research, e.g., on the mechanisms of corrosion resistance of stainless steels at the atomic level.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    A search is presented for pair production of heavy vector-like T and B quarks in proton-proton collisions at A root s = 13 TeV. The data sample corresponds to an integrated luminosity of 35.9 fb(-1), collected with the CMS detector at the CERN LHC in 2016. Pair production of T quarks would result in a wide range of final states, since vector-like T quarks of charge 2e/3 are predicted to decay to bW, tZ, and tH. Likewise, vector-like B quarks are predicted to decay to tW, bZ, and bH. Three channels are considered, corresponding to final states with a single lepton, two leptons with the same sign of the electric charge, or at least three leptons. The results exclude T quarks with masses below 1140-1300 GeV and B quarks with masses below 910-1240 GeV for various branching fraction combinations, extending the reach of previous CMS searches by 200-600 GeV.
  • Elm, Jonas; Hyttinen, Noora; Lin, Jack J.; Kurten, Theo; Prisle, Nonne L. (2019)
    The physical properties of small straight-chain dicarboxylic acids are well known to exhibit even/odd alternations with respect to the carbon chain length. For example, odd numbered diacids have lower melting points and higher saturation vapor pressures than adjacent even numbered diacids. This alternation has previously been explained in terms of solid-state properties, such as higher torsional strain of odd number diacids. Using quantum chemical methods, we demonstrate an additional contribution to this alternation in properties resulting from gas-phase dimer formation. Due to a combination of hydrogen bond strength and torsional strain, dimer formation in the gas phase occurs efficiently for glutaric acid (CS) and pimelic acid (C7) but is unfavorable for succinic acid (C4) and adipic acid (C6). Our results indicate that a significant fraction of the total atmospheric gas-phase concentration of glutaric and pimelic acid may consist of dimers.
  • Valiev, Rashid R.; Valiulina, Lenara I.; Fliegl, Heike; Sundholm, Dage (2020)
    The effect of anion complexation on magnetically induced current densities and excitation energies of antiaromatic molecular rings has been investigated by calculations on expanded antiaromatic porphyrinoids including orangarin, rosarin, amethyrin and on a theoretically predicted strongly antiaromatic hydrocarbon ring. Magnetically induced current densities and the lowest vertical excitation energies have been calculated at the density functional theory (DFT) and time-dependent DFT (TDDFT) levels using the M06-2X functional. Similar calculations have been performed on sapphyrin, cyclo[6]carbon and rubyrin, which are aromatic expanded porphyrinoids. The calculations show that anion complexation weakens the strength of the ring currents and the degree of (anti)aromaticity of the studied porphyrinoids and the antiaromatic hydrocarbon ring, because electronic charge is transferred from the anion to the molecular ring. The anion complexation weakens the calculated ring-current strength susceptibility of the antiaromatic porphyrinoids by 5-7 nA T-1 (25-30%), by 6-16 nA T-1 (21-48%) for the aromatic porphyrinoids, and by 8 nA T-1 (27%) for the antiaromatic hydrocarbon ring, whereas the current-density pathways remain the same for most molecules. Calculations on the lowest excited states show that the electronic excitation transfers electron density from the anion to the molecular ring. An antiaromatic heterocyclic molecular ring with five inner NH moieties that was constructed from the antiaromatic hydrocarbon ring was found to have a large Cl- complexation energy of 67.6 kcal mol(-1).