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  • 1.
    Carvalho, Alexandra
    et al.
    Department of Physics, I3N, University of Aveiro, Campus Santiago.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Briddon, Patrick R.
    Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Manzhos, Sergei
    Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore.
    Effect of the adsorption of ethylene carbonate on Si surfaces on the Li insertion behavior2013In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 585, p. 157-161Article in journal (Refereed)
    Abstract [en]

    Effects of the ethylene carbonate (EC) solvent on Li insertion and diffusion in Si anodes are studied using density functional theory. On both (100) and (111) reconstructed surfaces of Si, a semi-dissociated (SD) configuration of EC is stable and most favorable for Li insertion, lowering its barrier by up to 0.2 eV vs a clean surface. The less stable molecular adsorption has little effect on Li insertion and diffusion, while the surface ketone formed by dissociating the SD configuration at a cost of 0.6 eV has a strong detrimental effect on Li insertion, increasing its barrier by up to 0.4 eV.

  • 2. Edholm, O.
    et al.
    Ohlsson, P.I.
    Smith, M.L.
    Paul, Jan
    The barrier for heme-protein separation estimated by non-equilibrium molecular dynamics simulations1998In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 291, no 5-6, p. 501-508Article in journal (Refereed)
    Abstract [en]

    In heme-containing proteins the heme group is usually non-covalently bound in a pocket. Molecular dynamics (MD) simulations have been performed to estimate the barrier height for heme-protein separation. In simulations of myoglobin dissolved in water, a force has been applied to pull the heme out of the binding pocket. With forces above 0.5 nN, the heme group is easily pulled out of the pocket in times of the order of tens of picoseconds. With weaker forces, heme release becomes too slow to be monitored in an MD simulation covering a couple of hundred picoseconds. These results are consistent with a free energy barrier to heme release of about 100 kJ/mol. The results show that the main energetic change that occurs during the release is a conversion of heme/protein Lennard-Jones energy into heme/water Lennard-Jones energy. The release is essentially barrierless in energy indicating that the main part of the barrier is entropic.

  • 3.
    Estreicher, S.K.
    et al.
    Physics Department, Texas Tech University, Lubbock.
    Latham, Chris D.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Heggie, M.I.
    Department of Computer Science, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Stable and metastable states of C60H: buckminsterfullerene monohydride1992In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 196, no 3-4, p. 311-316Article in journal (Refereed)
    Abstract [en]

    Approximate ab initio Hartree-Fock and first-principles density functional calculations of potential energy surfaces and electronic structures of C60H show that the stable state has H attached to one C atom, outside the buckyball. This C atom is displaced radially outward and is close to being sp3 hybridized. The unpaired electron of C60H is delocalized. The calculated Fermi contact density at the proton is in good agreement with recent low-temperature μSR data. A metastable configuration has atomic H at the center of the ball (H@C60). Once trapped there, H must overcome a large barrier to go through the surface of C60. Other configurations we considered include H attached to one C atom but inside the buckyball, and H bridging one of the two inequivalent CC bonds. The barrier for diffusion of H from outside to the center of C60 have also been calculated. The results are compared to recent muon spin rotation studies in solid C60 and to the states of hydrogen in other forms of carbon.

  • 4.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Skodje, Rex T.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Probing stereodynamics in reactive collisions using helicity filtering2007In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 434, no 1-3, p. 20-24Article in journal (Refereed)
    Abstract [en]

    Stereodynamic effects in the D + H2 reaction are studied using a new method that permits reagent-helicity dependent cross sections to be inferred from the scattering results obtained using randomly oriented reagent molecules. Employing fully converged quantum scattering calculations as a benchmark, it is demonstrated that the method yields useful results for all the helicity states corresponding to j = 1 and 2 of the H2 diatom.

  • 5.
    Hochberg, David
    et al.
    Centro de Astrobiología (CSIC-INTA).
    Zorzano, María Paz
    Centro de Astrobiología (CSIC-INTA).
    Reaction-noise induced homochirality2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 431, no 1-3, p. 185-189Article in journal (Refereed)
    Abstract [en]

    Starting from the chemical master equation, we employ field theoretic techniques to derive Langevin-type equations that exactly describe the stochastic dynamics of the Frank chiral amplification model with spatial diffusion. The intrinsic multiplicative noise properties are completely and rigorously derived by this procedure. We carry out numerical simulations in two spatial dimensions. When the inherent spatio-temporal fluctuations are properly included, then complete chiral amplification results from a purely racemic initial configuration. Phase separation can also arise in which the enantiomers coexist in spatially segregated domains separated by a sharp racemic interface or boundary.

  • 6.
    Hochberg, David
    et al.
    Centro de Astrobiología (CSIC-INTA).
    Zorzano, María Paz
    Centro de Astrobiología (CSIC-INTA).
    Morán, Federico
    Centro de Astrobiología (CSIC-INTA).
    Complex reaction noise in a molecular quasispecies model2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 423, no 1-3, p. 54-58Article in journal (Refereed)
    Abstract [en]

    We have derived exact Langevin equations for a model of quasispecies dynamics. The inherent multiplicative reaction noise is complex and its statistical properties are specified completely. The numerical simulation of the complex Langevin equations is carried out using the Cholesky decomposition for the noise covariance matrix. This internal noise, which is due to diffusion-limited reactions, produces unavoidable spatio-temporal density fluctuations about the mean field value. In two dimensions, this noise strictly vanishes only in the perfectly mixed limit, a situation difficult to attain in practice

  • 7. Kundu, Tarun
    et al.
    Rao, K. Hanumantha
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    S.C., Parker
    University of Bath.
    Atomistic simulation of the surface structure of wollastonite2003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 377, no 1-2, p. 81-92Article in journal (Refereed)
    Abstract [en]

    Atomistic simulation techniques have been used to calculate the surface structure and stability of wollastonite crystal. Seven predominant surfaces have been modelled and their calculated surface energy corresponds well with their morphological domination. The surface energy, hydration energy and reaction energy values indicate wollastonite surfaces stabilized to great extent by adsorbing water in dissociated form. The Ca2+ replacement from the first few layers of the surface is found to be energetically more favourable, elucidating high dissolution phenomena of wollastonite mineral.

  • 8.
    Lindgren, S.Å.
    et al.
    Chalmers University of Technology.
    Paul, Jan
    Walldén, L.
    Chalmers University of Technology.
    Photoemission of backbonding electrons from CO chemisorbed on Cu(III)1981In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 84, no 3, p. 487-490Article in journal (Refereed)
    Abstract [en]

    Angle-resolved photoclectron energy spectra recorded in the normal direction for a CO-exposed Cu(111) sample show a peak at the Fermi edge for high monolayer coverages. We associate this peak with a filled part of a resonance-broadened CO 2π level.

  • 9.
    Malysheva, Lyuba
    et al.
    Bogolyubov Institute for Theoretical Physics, Kiev.
    Klymenko, Yuriy
    Space Research Institute, Kiev.
    Onipko, Alexander
    Valiokas, Ramünas
    Division of Sensor Science and Molecular Physics, Department of Physics and Measurement Technology, Linköping University.
    Liedberg, Bo
    Division of Sensor Science and Molecular Physics, Department of Physics and Measurement Technology, Linköping University.
    Ab initio calculations of equilibrium geometries and vibrational excitations of helical ethylene-glycol oligomers: Application to modeling of monolayer infrared spectra2003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 370, no 3-4, p. 451-459Article in journal (Refereed)
    Abstract [en]

    The density functional theory methods are used to calculate the equilibrium molecular structures and vibrational spectra of helical H(CH2CH2O)nH (OEG) oligomers (n = 4-7) at a level of precision that has not been accomplished before. The largest deviation between experimentally observed frequencies, obtained from infrared reflection-absorption spectra of OEG-monolayers on gold, and calculated, single molecule frequencies (unscaled), is slightly above 2%. Moreover, the most intense peak in the CH2-stretching region at about 2890 cm-1, commonly regarded as a trademark of the OEG helical conformation, is reassigned in this study to the asymmetric CH2-stretching mode

  • 10. Paul, Jan
    et al.
    Hoffman, F.M.
    CO adsorption on clean and oxidized Al(110)1986In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 130, no 3, p. 160-163Article in journal (Refereed)
    Abstract [en]

    Electron-energy loss (EELS) spectra and thermal desorption (TDS) traces of carbon monoxide bound to the (100) surface of aluminum are presented. CO chemisorption on clean Al(100) is characterized by vibrational bands at 440 and 2060 cm-1 and by desorption at 125 K. Oxide "islands", formed by oxidation in O2 at 575 K, have no observed electronic influence on open metallic areas of the adsorbent but merely block CO adsorption sites.

  • 11. Paul, Jan
    et al.
    Lundberg, M.
    A working procedure for the evaluation of exafs phase shifts: application to Cu(111)/Cs1985In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 117, no 5, p. 511-513Article in journal (Refereed)
    Abstract [en]

    A theoretical procedure is presented to evaluate EXAFS phase shifts. The procedure is based on a self-consistently determined ground-state electron density and an energy-dependent complex scattering potential. Most EXAFS or NEXAFS/XANES schemes used today apply a constant imaginary part of the scattering potential. We illustrate our procedure by calculations on cesium atoms adsorbed onto Cu(111).

  • 12. Paul, Jan
    et al.
    Ohlsson, P.I.
    Chen, W.
    Temperature dependence of CO ligation to LegHb and Mb: 0-80°C1994In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 231, no 4-6, p. 547-550Article in journal (Refereed)
    Abstract [en]

    The temperature dependence of the coordination of CO to two hemoproteins, myoglobin (Mb) and leghemoglobin (LegHb), has been studied by absorption spectroscopy. All spectral changes in the electronic and infrared ranges are fully reversible between 8 and 88°C and indicate a more linear orientation of the distal ligand with increasing temperature. The characteristic energy for the above spectral changes is around 200 cm-1 or identical to the Fe-Imidazole (Im) mode in hemoproteins. Our results are also compared with recent models for the dynamics of CO adsorbed at the surfaces of transition metals. Based on these surface models we suggest that our observed temperature dependences stem from thermal excitations of the Fe-Im vibration. This implies a so far undocumented mechanism by which the Fe-proximal bond influences the binding and energy dissipation at the active site of hemoproteins.

  • 13. Paul, Jan
    et al.
    Rosén, A.
    Chalmers University of Technology.
    Hydrogen bonding between liganded CO and heme-proteins1984In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 105, no 2, p. 197-200Article in journal (Refereed)
    Abstract [en]

    Perturbations of the CO bond in carbon monoxide bound to iron in different heme-proteins are discussed. Properties evaluated from Hartree-Fock-Slater electronic structure calculations are correlated with experimental observations. The net charge on oxygen (HFS) is related to the Fe(III)/Fe(II) reduction potential (EMF). Consequently, proteins with low EMF, e.g. peroxidases, have more ability to form FeCOH...H. protein hydrogen bonds than, for example, oxidases with higher EMF. This can explain anomalous vibrational frequencies, νCO, observed for acidified peroxidases. Calculations reveal that direct interaction between CO and polar groups on the protein can cause peturbations of the CO π-bond order similar to those from EMF shifts. Dioxygen and carbon monoxide are compared in regard to hydrogen bonding to heme-proteins.

  • 14. Persson, P-A
    et al.
    Edlund, U.
    Jacobsson, P.
    Johnels, D.
    Soldatov, Alexander
    Sundqvist, Bertil
    NMR and Raman characterization of pressure polymerized C601996In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 258, no 5-6, p. 540-546Article in journal (Refereed)
    Abstract [en]

    Bulk C60 has been treated at 1.1 GPa and 550-585 K, producing a dense insoluble material which on heating to above 600 K reverts to normal C60. Raman and IR studies on modified material show a large number of new lines, and the Raman pentagon pinch mode shifts from 1469 to 1458 cm-1 as on photopolymerization. MAS NMR shows one broadened line at the original C60 shift 144 ppm and a small peak at about 77 ppm due to the bridging carbons. None of the new resonances observed for C60 polymerized by other methods were observed. The results verify previously suggested polymeric structures where the fullerence cages are connected by four-membered rings.

  • 15.
    Song, Zhiyan
    et al.
    Stockholm University.
    Antzutkin, Oleg
    Rupprecht, Allan
    Stockholm University.
    Order-resolved sideband separation in magic-angle-spinning NMR. 31P NMR of oriented DNA fibers1996In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 253, no 3-4, p. 349-354Article in journal (Refereed)
    Abstract [en]

    We report new radiofrequency pulse schemes for deriving the orientation distribution function of chemical shift anisotropy tensors in the nuclear magnetic resonance of ordered solids. Sample spinning at the magic-angle is combined with radio frequency pulse schemesfor spinning sideband separation. We separate the sidebands associated with molecular order using only 5 radiofrequency π-pulses and avoiding a three-dimentional Fourier transformation.

1 - 15 of 15
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