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  • 51.
    Liu, Yuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    C-13 Chemical Shift in Natural Gas Hydrates from First-Principles Solid-State NMR Calculations2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 2, p. 1130-1136Article in journal (Refereed)
    Abstract [en]

    Natural gas hydrates (NGHs) are of interest both as a prospective energy resource and for possible technological applications. C-13 NMR technology is a powerful tool to characterize NGHs, and in this work, the trends and origins of C-13 NMR chemical shifts of hydrocarbon molecules in NGHs from quantum-chemical first-principles calculations on solid state phases are presented. The chemical shift is found to decrease as the size of the water cavities increases for single occupancy NGHs, and to increase as the amount of CH4 increases for the multioccupancy cases. In most cases, the chemical shift of NGHs monotonically increases as the external pressure increases. Furthermore, the chemical shift can be mainly attributed to the host-guest interaction together with a small contributions from water molecules for tight environments and mainly depends on host-guest interaction for loose environments. The theoretical results provide useful information for identification of the types of clathrate phases and guest molecules included in NGH samples taken from natural sites.

  • 52.
    Liu, Yuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    C-C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study2014In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 49, p. 11641-11651Article in journal (Refereed)
    Abstract [en]

    The presence of specific hydrocarbon gas molecules in various types of water cavities in natural gas hydrates (NGHs) are governed by the relative stabilities of these encapsulated guest molecule-water cavity combinations. Using molecular quantum chemical dispersion-corrected hybrid density functional computations, the interaction (Delta E(host-)guest) and cohesive energies (Delta E-coh), enthalpies, and Gibbs free energies for the complexes of host water cages and hydrocarbon guest molecules are calculated at the pi B97X-D/6-311++G(2d,2p) level of theory. The zero-point energy effect of ?Ehost-guest and ?Ecoh is found to be quite substantial. The energetically optimal host-guest combinations for seven hydrocarbon gas molecules (CH4, C2H6, C3H6, C3H8, C4H8, i-C4H10, and n-C4H10) and various water cavities (D, ID, T, P, H, and I) in NGHs are found to be CH4@D, C2H6@T, C3H6@T, C3H8@T, C4H8@T/P/H, i-C4H10@H, and n-C4H10@H, as the largest cohesive energy magnitudes will be obtained with these host-guest combinations. The stabilities of various water cavities enclosing hydrocarbon molecules are evaluated from the computed cohesive Gibbs free energies: CH4 prefers to be trapped in a ID cage; C2H6 prefer T cages; C3H6 and C3H8 prefer T and H cages; C4H8 and i-C4H10 prefer H cages; and n-C4H10 prefer I cages. The vibrational frequencies and Raman intensities of the C-C stretching vibrational modes for these seven hydrocarbon molecules enclosed in each water cavity are computed. A blue shift results after the guest molecule is trapped from gas phase into various water cages due to the host-guest interactions between the water cage and hydrocarbon molecule. The frequency shifts to the red as the radius of water cages increases. The model calculations support the view that C-C stretching vibrations of hydrocarbon molecules in the water cavities can be used as a tool to identify the types of crystal phases and guest molecules in NGHs.

  • 53.
    Liu, Yuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering. Not Found:Linkoping Univ, Dept Chem, IFM, SE-58183 Linkoping, Sweden.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    CH-Stretching Vibrational Trends in Natural Gas Hydrates Studied by Quantum-Chemical Computations2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 30, p. 17084-17091Article in journal (Refereed)
    Abstract [en]

    Vibrational Raman spectrosopy of hydrocarbon CH-stretching vibrations is often-used to study natural gas, hydrates., In this work, CH-stretching vibrational, Raman spectra of hydrocarbon molectles (CH4, C2H6, C(3)H6, C3H8, C4H8, i-C4H10, and n-C4H10) encapsulated in the water cages (D, ID, T, P, H, and I) of the SI, sII, sH, and sK crystal phases. are derived from quantum-chemical computations at the omega B97X-D/6-311++G(24,2p) level of theory. The trends of CH-stretching vibrational frequencies Of hydrocarbon Molecules in natural gas hydrates are found to follow the prediction by the loose cage tight cage model: as the size of Water cavity increases, the CH frequencies will first decrease and: then increase until equal to-that in the gas phase. In the "tight cage" situation, the frequency will be greater than in the gas phase; in the "loose cage" situation, the frequency will be smaller or asymptotic to that in the gas phase. Furthermore, the OH-stretching frequencies are sensitive to the H-bond configuration, and the varying strengths of H-bonds for different configurations are reflected by,the frequency distribution in the corresponding subspectra.

  • 54.
    Liu, Yuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering. Beijing Univ Chem Technol, Peoples R China.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Clathrate ice sL: a new crystalline phase of ice with ultralow density predicted by first-principles phase diagram computations2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 12, p. 8333-8340Article in journal (Refereed)
    Abstract [en]

    In contrast to the rich knowledge of water and 17 experimentally confirmed crystalline phases of solid water under positive pressures, water under negative pressure has been poorly explored. In this study, a new crystalline phase of ice with ultralow density (0.6 g cm(-3)), named clathrate ice sL, is constructed by nano water cage clusters, and it is predicted to be stable under a lower negative pressure than the experimentally confirmed sII phase by first-principles phase diagram computations, thereby extending the phase diagram of water to negative pressure regions below -5170 bar at 0 K and below -4761 bar at 300 K. In addition, according to our theoretical prediction, the optimal hydrogen storage mass density in the new clathrate ice sL is 7.7 wt% (larger than the 2017 DOE target of 5.5 wt%), which would set a new record of hydrogen storage capacity in clathrate hydrates. The finding of clathrate ice sL not only proposes a new type of crystalline ice under negative pressure but also explores the potential applications of the ultralow density ice phases while extending the water phase diagram and enriching the knowledge of people about water.

  • 55.
    Liu, Yuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Fingerprints in IR OH vibrational spectra of H2O clusters from different H-bond conformations by means of quantum-chemical computations2014In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 20, no 6, p. 2281-Article in journal (Refereed)
    Abstract [en]

    The thermodynamic stabilities and IR spectra of the three water clusters (H2O)(20), (H2O)(54,), and (H2O)(100) are studied by quantum-chemical computations. After full optimization of the (H2O)(20,54,100) structures using the hybrid density functional B3LYP together with the 6-31+G(d,p) basis set, the electronic energies, zero-point energies, internal energies, enthalpies, entropies, and Gibbs free energies of the water clusters at 298 K are investigated. The OH stretching vibrational IR spectra of (H2O)(20,54,100) are simulated and split into sub-spectra for different H-bond groups depending on the conformations of the hydrogen bonds. From the computed spectra the different spectroscopic fingerprint features of water molecules in different H-bond conformations in the water clusters are inferred.

  • 56.
    Liu, Yuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Raman and IR Spectra of Ice Ih and Ice XI with an Assessment of DFT Methods2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 42, p. 11043-11051Article in journal (Refereed)
    Abstract [en]

    IR and Raman spectroscopic technology can be directly used to identify the occurrence of ferroelectric ice XI in laboratory or extraterrestrial settings. The performance of 16 different DFT methods applied on the ice Ih, VIII, IX, and XI crystal phases is evaluated. Based on a selected DFT computational scheme, the IR and Raman spectra of ice Ih and XI are derived and compared. When the spectra, both IR and Raman, of ice Ih and ice XI are compared, the librational vibrations are found to be the most affected by the proton ordering. The spectroscopic fingerprint of ice XI can be used to distinguish ferroelectric ice XI from ice Ih in the universe. Furthermore, the existence of only one kind of H-bond in ice Ih is demonstrated from the overlapping subspectra for different types of H-bonded pair configurations in 16 isomers of ice Ih, which provides an illustration to the historic debate on whether one or two kinds of H-bonds existed in ice.

  • 57.
    Lloyd Spetz, Anita
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics. Linköping University, The Institute of Technology.
    Skoglundh, Magnus
    Applied Surface Chemistry, Chalmers University, Sweden.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    FET sensors gas sensing mechanism, experimental and theoretical studies2009In: Solid State Gas Sensing: Fundamentals and new trends in gas sensing, US: Springer , 2009, XV, p. 153-(27pp)Chapter in book (Other academic)
    Abstract [en]

    The chemical gas sensor area has gained large improvements from the

    nanoscience technology, e.g., more reproducible processing including control

    on the nanoscale of annealing procedures, which implies improved long-term

    stability. Analytical tools have developed towards detection and investigation

    of ever smaller size phenomena. This has been of importance for the key

    problem of chemical gas sensors, the detailed understanding on the nanoscale

    level of the gas-sensing mechanism. In this chapter, which deals with FET (field

    effect transistor) gas sensor devices, we will review analytical tools that provide

    information about the detection mechanism with special emphasise on the FET

    sensor area. The DRIFT, diffuse reflection infrared Fourier transform, spectroscopy

    as a rather new and very important tool is reviewed. Theoretical modelling

    will speed up the process to provide further details in the mechanistic

    studies. Examples will be given in this chapter. A number of other important

    analytical tools will be briefly described.

  • 58.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Salomonsson, Anette
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Käll, Per-Olov
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Strand, M.
    Einvall, J.
    Aulin, C.
    Nanoparticles as sensing material for selective and stable SiC-FET gas sensor2006In: Proc. European Aerosol Conference 2005,2006, 2006, p. 735-735Conference paper (Refereed)
  • 59.
    Lunell, S
    et al.
    Uppsala universitet, Institutionen för kvantkemi.
    Stashans, A
    Ojamae, L
    Lindström, H
    Uppsala universitet, Fysikalisk-kemiska institutionen.
    Hagfeldt, Anders
    Uppsala universitet, Fysikalisk-kemiska institutionen.
    Li and Na diffusion in TiO2 from quantum chemical theory versus electrochemical experiment1997In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 119, no 31, p. 7374-7380Article in journal (Refereed)
    Abstract [en]

    Diffusion of Li and Na ions in TiO2, anatase, has been studied using theoretical (quantum chemical nb initio periodic Hartree-Fock and a modified semiempirical INDO) as well as electrochemical (chronocoloumetry) methods. On the basis of the theoretical ca

  • 60.
    Lutic, D.
    et al.
    Växjö universitet.
    Strand, M.
    Växjö universitet.
    Salomonsson, Anette
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Käll, Per-Olov
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Sanati, M.
    Växjö universitet.
    In2O3 particle films as gate material for MISiC-capacitor sensors2005In: NOSA 2005,2005, 2005Conference paper (Refereed)
  • 61. McDonald, S
    et al.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Singer, Sherwin J.
    Graph theoretical generation and analysis of hydrogen-bonded structures with applications to the neutral and protonated water cube and dodecahedral clusters1998In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 102, no 17, p. 2824-2832Article in journal (Refereed)
    Abstract [en]

    Graph theoretical techniques are demonstrated to be of considerable use in the search for stable arrangements of water clusters. inspired by the so-called "ice rules" that govern which hydrogen-bond networks are physically possible in the condensed phase, we use graphical techniques to generate a multitude of local minima of neutral and protonated water clusters using oriented graph theory. Efficient techniques to precisely enumerate all possible hydrogen-bonding topologies are presented. Empirical rules regarding favorable water neighbor geometries are developed that indicate which of the multitude of hydrogen-bonding topologies available to large water clathrates (e.g., 30 026 for (H2O)(20)) are likely to be the most stable structures. The cubic (H2O)(8) and dodecahedral (H2O)(20) clusters and their protonated analogues are treated as examples. In these structures every molecule is hydrogen bonded to three others, which lends to hydrogen-bonding topology fixing the cluster geometry. Graphical techniques can also be applied to geometrically irregular structures as well. The enumerated oriented graphs are used to generate initial guesses for optimization using various potential models. The hydrogen-bonding topology was found to have a significant effect on cluster stability, even though the total number of hydrogen bonds is conserved. For neutral clusters, the relationship between oriented graphs and local minima of several potential models appears to be one-to-one. The stability of the different topologies is rationalized primarily in terms of the number of nearest neighbor pairs that both have a free OH bond. This lends to the identification of water dodecahedra of greatest stability.

  • 62.
    Myneni, S.
    et al.
    Earth Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA, Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
    Luo, Y
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden, Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Näslund, L. Å.
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Cavalleri, M.
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden.
    Ojamäe, L.
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Ogasawara, H
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden, Permanent address: RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan..
    Pelmenschikov, A.
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden.
    Wernet, Ph.
    Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    Heske, C.
    Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA.
    Hussain, Z
    Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA.
    Pettersson, L. G. M.
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden.
    Nilsson, A.
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden, Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    Spectroscopic probing of local hydrogen-bonding structures in liquid water2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 8, p. L213-L219Article in journal (Refereed)
    Abstract [en]

    We have studied the electronic structure of liquid water using x-ray absorption spectroscopy at the oxygen K edge. Since the x-ray absorption process takes less than a femtosecond, it allows probing of the molecular orbital structure of frozen, local geometries of water molecules at a timescale that has not previously been accessible. Our results indicate that the electronic structure of liquid water is significantly different from that of the solid and gaseous forms, resulting in a pronounced pre-edge feature below the main absorption edge in the spectrum. Theoretical calculations of these spectra suggest that this feature originates from specific configurations of water, for which the H-bond is broken on the H-donating site of the water molecule. This study provides a fingerprint for identifying broken donating H-bonds in the liquid and shows that an unsaturated H-bonding environment exists for a dominating fraction of the water molecules.

  • 63. Nilsing, M
    et al.
    Lunell, S
    Persson, P
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Phosphonic acid adsorption at the TiO2 anatase (101) surface investigated by periodic hybrid HF-DFT computations,2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 582, p. 49-60Article in journal (Refereed)
  • 64. Nilsing, M
    et al.
    Persson, P
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Anchor group influence on molecule-metal oxide interfaces: periodic hybrid DFT study of pyridine bound to TiO2 via carboxylic and phosphonic acid2005In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 415, p. 375-380Article in journal (Refereed)
  • 65. Nilsing, Mattias
    et al.
    Persson, Petter
    Lunell, Sten
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry.
    Dye-sensitization of the TiO2 rutile (110) surface by perylene dyes: Quantum-chemical periodic B3LYP computations2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 32, p. 12116-12123Article in journal (Refereed)
    Abstract [en]

    The adsorption of perylene derivatives on the rutile TiO2(110) surface was studied by quantum-chemical periodic calculations employing the hybrid HF-DFT functional B3LYP. The perylene molecule, which is a possible constituent of dyes in dye-sensitized solar cells, was functionalized by attachment of phosphonic acid or carboxylic acid groups to permit anchoring to the metal oxide surface. The anchor groups were bound to the molecule directly or via different spacer groups, namely --CH2-, -CH2-CH2-, and -CH = CH-. The effects of the anchor and spacer groups on the adsorption geometry and energy, on the electronic structure of the dye-TiO2 interface, and on the electron transfer rates were investigated. The phosphonic acid anchor group was found to bind the perylene derivatives much more strongly to the surface than the carboxylic acid anchor group. The spacer groups were capable of significantly altering electron transfer rates across the dye-metal oxide interface, where the unsaturated groups permitted injection times in the low femtosecond regime.

  • 66.
    Nilsson, A
    et al.
    Stanford Synchrotron Radiation Laboratory, Stanford, USA.
    Wernet, Ph
    Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung, Berlin, Germany.
    Nordlund, D
    Stanford Synchrotron Radiation Laboratory, USA.
    Bergmann, U
    Fysikum, AlbaNova University Center, Sweden.
    Cavalleri, M
    Stanford Synchrotron Radiation Laboratory, USA.
    Odelius, M
    Fysikum, AlbaNova University Center, Sweden.
    Ogasawara, H
    Stanford Synchrotron Radiation Laboratory, USA.
    Näslund, L.Å.
    Fysikum, AlbaNova University Center, Sweden.
    Hirsch, T.K.
    Stanford Synchrotron Radiation Laboratory, USA.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    Glatzel, P
    Swiss Norwegian Beamlines, European Synchrotron Radiation Facility, Grenoble, France.
    Pettersson, L.G.M.
    Fysikum, AlbaNova University Center, USA.
    Comment on "energetics of hydrogen bond network rearrangements in liquid water": in Science / American Association for the Advancement of Science, vol 308, pg 7932005In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 308, no 5723, p. 793-793Article in journal (Other academic)
  • 67. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    AB-INITIO STUDY OF COOPERATIVITY IN WATER CHAINS - BINDING-ENERGIES AND ANHARMONIC FREQUENCIES1994In: J PHYS CHEM-US, ISSN 0022-3654, Vol. 98, no 16, p. 4271-4282Article in journal (Refereed)
    Abstract [en]

    Many-body interaction energies and anharmonic OH stretching frequencies have been calculated for water in chain formations, in a ring structure, and in a tetrahedral arrangement. The calculations were of ab initio type, with the electron correlation energy included by Moller-Plesset perturbation correction to second order (MP2) and the basis-set superposition error corrected by the counterpoise procedure. The maximum chain length was seven water molecules, and the ring was five-membered. The molecules were H-bonded head-to-tail. The two- and many-body energies for the chains and ring are all of the same sign (negative), indicating strong cooperativity. The total nonadditivity contribution to the interaction energy is large, 16% for the longest chain and over 18% for the ring. The interaction energy of ah individual chain member with the rest of the chain shows even larger nonadditivity: over 25% for a molecule in the middle of the chain. This quantity should be of relevance for molecular dynamics simulations of liquid water. The OH stretching frequency downshift increases for all members of the chain with increasing chain length and is larger for molecules in the interior of the chain (-357 cm(-1) for the middle molecule in the 7-chain) than for terminal water molecules. The frequency converges only slowly for water molecules in the interior but faster for terminal water molecules. ''Frequency cooperativity'' was investigated by calculating many-body contributions in a manner analogous to the energy calculations. The chain and ring exhibit strong cooperativity. Infrared absorption intensities and charge transfer were investigated.

  • 68. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    CRYSTAL ABINITIO INVESTIGATIONS OF ICE-II, ICE-VIII AND ICE-IX1994In: HYDROGEN BOND NETWORKS, 1994, p. 411-418Conference paper (Refereed)
  • 69. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    THE OH STRETCHING FREQUENCY IN LICLO4-BULLET-3H2O(S) FROM ABINITIO AND MODEL POTENTIAL CALCULATIONS1992In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 161, no 1-2, p. 87-98Article in journal (Refereed)
    Abstract [en]

    The "in-crystal" frequency of the anharmonic and uncoupled OH stretching vibration of HDO molecules in LiClO4.3H2O(s) has been calculated by quantum-mechanical ab initio and model potential methods and compared with the experimental infrared frequency from isotope-isolated HDO molecules. The effects of the nearest neighbours as well as of the crystalline environment have been investigated by the two computational techniques. In both cases, the one-dimensional potential for an anharmonic OH oscillator was constructed from point-wise energy calculations and the Schrodinger equation for the protonic motion in this potential well was solved by a variational procedure. In the ab initio calculations, vibrational potentials were constructed from RHF and MP2 type calculations of point-charge embedded ClO4-.HDO and (Li+)2.(ClO4-)2.HDO clusters using DZP and TZP basis sets. For the LiClO4.3H2O(s) crystal, the ab initio OH frequency is in close quantitative agreement with experiment when electron correlation by MP2 and the crystal field are included: 3537 cm-1 (MP2(TZP)) versus the experimental value of 3556 cm-1. Inclusion of the crystal field is essential and can in this crystal be satisfactorily represented by Ewald field-consistent point charges outside the hydrogen-bonded ClO4-...HDO cluster. In the model potential calculations, analytical intermolecular pair potential functions from the literature were used in conjunction with an experimental intramolecular potential function for the OH stretching motion. The particular intermolecular model chosen here yields an absolute OH frequency 160 cm-1 below experiment. These calculations exemplify some of the difficulties encountered when employing analytical model potentials in vibrational studies.

  • 70. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    WATER-MOLECULES IN DIFFERENT CRYSTAL SURROUNDINGS - VIBRATIONAL O-H FREQUENCIES FROM ABINITIO CALCULATIONS1992In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 96, no 12, p. 9035-9045Article in journal (Refereed)
    Abstract [en]

    Ab initio quantum-mechanical calculations of anharmonic frequencies for the water O-H vibrations have been performed for a series of crystalline hydrates. In each case, the potential-energy curve for the uncoupled water O-H stretch was derived at the Moller-Plesset MP2 level. Nearest neighbors of the water molecule were explicitly included in the supermolecule and the rest of the surroundings were mimicked by point charges to reproduce the crystal field out to infinity. The time-independent Schrodinger equation for the motion of the proton in this potential well was solved variationally and the frequency was obtained from the energy difference between the 0 and 1 eigenstates. Computed frequencies can be directly compared with existing infrared data for isotope-isolated water molecules in these hydrates. The compounds selected (LiClO4.3H2O, LiHCOO.H2O, LiOH.H2O) exhibit experimental O-H frequency shifts in a wide range, from - 150 down to - 930 cm-1. Good agreement is found between experimental and theoretical frequencies (experimental values in parentheses): 3596 (3556) for LiClO4.3H2O, 3129 (3112) and 3488 (3390) for LiHCOO.H2O, and 2817 (2775) cm-1 for LiOH.H2O. Correlation curves of typical H-bond parameters such as nu(O-H) vs R(H...O), r(e)(O-H) and nu(OH)/nu(OD) have been computed and compared with experiment. The vibrational intensities are also discussed.

  • 71. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    DOVESI, ROBERTO
    ROETTI, CARLA
    SAUNDERS, VR
    MECHANICAL AND MOLECULAR-PROPERTIES OF ICE-VIII FROM CRYSTAL-ORBITAL AB-INITIO CALCULATIONS1994In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 100, no 3, p. 2128-2138Article in journal (Refereed)
    Abstract [en]

    The proton-ordered ice VIII structure has been investigated by ab initio periodic Hartree-Fock calculations in the pressure interval from 0 to 30 GPa using a 6-31G** basis set, The structure was optimized by energy-minimization at different volumes, and from the resulting energy vs volume relationship; the equation of state of ice VIII was derived; The variation of the structure,intramolecular geometry, Mulliken charges, electron density, Raman spectrum, and infrared stretching vibrations with varying pressure were investigated. The agreement with existing experimental data is generally good. Nearest-neighbor hydrogen-bonded O...O distances decrease from 2.88 to 2.57 Angstrom as the pressure is increased from 0 to 30 GPa. For the same: pressure range, the intramolecular OH bond increases from 0.951 to 0.955 Angstrom (giving a dr(OH)/dP value of 0.000 14 Angstrom/GPA), the Mulliken charge on H increases from +0.386 to +0.452, the calculated bulk modulus increases from similar to 25 to similar to 160 GPa), (corresponding experimental values ire similar to 25 at 2.4 GPa and similar to 135 at 30 GPa), and the electron density redistribution is considerably enhanced. The frequency downshift of the OH stretching vibration varies from -200 cm(-1) at 2.4 GPa to -500 cm(-1) at 20 GPa; the corresponding experimental values are -300 and -650 cm(-1). Electronic density-of-states diagrams are presented.

  • 72. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    PISANI, CESARE
    CAUSA, MAURO
    ROETTI, CARLA
    STRUCTURAL, VIBRATIONAL AND ELECTRONIC-PROPERTIES OF A CRYSTALLINE HYDRATE FROM AB-INITIO PERIODIC HARTREE-FOCK CALCULATIONS1994In: Acta Crystallographica Section B: Structural Science, ISSN 0108-7681, E-ISSN 1600-5740, Vol. 50, p. 268-279Article in journal (Refereed)
    Abstract [en]

    The hydrate crystal lithium hydroxide monohydrate LiOH.H2O has been studied by ab initio periodic Hartree-Fock calculations. The influence of the crystalline environment on the local molecular properties (molecular geometry, atomic charges, electron density, molecular vibrations and deuterium quadrupole coupling constants) of the water molecule, the lithium and hydroxide ions has been calculated. A number of crystalline bulk properties are also presented, optimized crystalline structure, lattice energy and electronic band structure. The optimized cell parameters from calculations with a large basis set of triple-zeta quality differ by only 1-3% from the experimental neutron-determined cell, whereas the STO-3g basis set performs poorly (differences of 5-10%). With the triple-zeta basis also the atomic positions and intermolecular distances agree very well with the experiment. The lattice energy differs by approximately 8% from the experimental value, and by at most 3% when a density-functional electron correlation correction is applied. Large electron-density rearrangements occur in the water molecule and in the hydrogen bond and are in qualitative and quantitative agreement with experimental X-ray diffraction results. The quadrupole-coupling constants of the water and hydroxide deuterium atoms are found to be very sensitive to the O-H bond length and are in good agreement with experimental values when the calculation is based on the experimental structure. The anharmonic O-H stretching vibrations in the crystal are presented and found to be very close to results from calculations on molecular clusters. The electronic band and density-of-states spectra are discussed. Model calculations on a hydrogen fluoride chain were used to rationalize the results.

  • 73. OJAMAE, LARS
    et al.
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    PROBST, MICHAEL
    THE OH STRETCHING FREQUENCY IN LIQUID WATER SIMULATIONS - THE CLASSICAL ERROR1992In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 191, no 5, p. 500-506Article in journal (Refereed)
    Abstract [en]

    OH stretching frequencies of HDO molecules in liquid water have been calculated by molecular dynamics simulation and compared to quantum-corrected OH stretching frequencies. In the MD simulation the MCY intermolecular water-water potential was used together with an experimental intramolecular free water potential. The frequencies calculated classically by Fourier transformation of the velocity autocorrelation function are found to be almost-equal-to 300 cm-1 too high compared with experiment. Quantum corrections show that the classical error contribution to this discrepancy is almost-equal-to 140 cm-1. To reach full agreement with experiment also the potential model needs to be improved. It is suggested that in constructing flexible water potentials the goal should not be set for an MD-derived OH frequency in absolute agreement with experiment (at 3400 cm-1) but instead some 200 cm-1 higher.

  • 74. OJAMAE, LARS
    et al.
    TEGENFELDT, JÖRGEN
    LINDGREN, JAN
    HERMANSSON, KERSTI
    Uppsala universitet, Kemiska institutionen.
    SIMULATION OF BAND WIDTHS IN LIQUID WATER SPECTRA - THE BREAKDOWN OF THE FROZEN-FIELD APPROXIMATION1992In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 195, no 1, p. 97-103Article in journal (Refereed)
    Abstract [en]

    Band shapes of liquid water OH vibrational spectra oblained from molecular dynamics (MD) simulation and from a quantum-mechanical method are investigated. The so-called "frozen-field approximation" applied to the calculation of quantum-mechanical high-frequency vibrational spectra is critically examined. It is demonstrated that the band width of the OH stretching spectrum is seriously overestimated through the neglect of the dynamics of the environment in the frozen-field approximation. We show that the proper inclusion of the dynamics in this quantum-mechanical method leads not only to a correct absolute frequency for the model potential used, but also to the correct description of the band width. The basic steps in this method are: (1) an MD simulation yielding an ensemble of liquid water configurations, (2) a quantum-mechanical uncoupled local-mode calculation of the OH frequency for each molecule, using model potentials for the inter- and intra-molecular interactions, (3) inclusion of the influence from the dynamics of the surroundings by filtering out rapid frequency fluctuations. The remaining discrepancy between experimental and computed OH spectra is attributed to shortcomings in the potential model used.

  • 75.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    CRYSTALLINE ICE Amorphous on the surface2011In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 10, no 10, p. 725-726Article in journal (Other academic)
    Abstract [en]

    Crystalline ice surfaces are found to exhibit an unusually large spread of vacancy formation energies, akin to an amorphous material. The finding has implications for the fundamental understanding of electrostatically frustrated surfaces and for the reactivity and catalytic properties of atmospheric ice. Watkins et al. have found that even for a perfect ice surface, a clean-cut surface where the oxygen atoms are ordered in a hexagonal lattice, the energy needed to form a vacancy varies greatly depending on the water molecule removed. They found that at interfaces, nearest-neighbor water molecules cannot satisfy all hydrogen bonds, and thus some of the molecules exhibit dangling OH bonds. The findings of Watkins and co-authors imply that ice may possess more surface vacancies than expected. The ab initio molecular dynamics simulations of model ice surfaces show that surface molecules can be thermally activated below the model's melting point to form vacancies and adsorbed molecules at the surface.

  • 76.
    Ojamäe, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet.
    The water molecule in gaseous, liquid and solid surroundings: an ab initio and molecular dynamics study1993Doctoral thesis, comprehensive summary (Other academic)
  • 77.
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Water and functionalized nanocrystals2006In: National Supercomputer Centre news, no 2Article in journal (Other academic)
    Abstract [en]

      

  • 78.
    Ojamäe, Lars
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Aulin, Christian
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Käll, Per-Olov
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    IR and quantum-chemical studies of carboxylic acid and glycine adsorption on rutile TiO2 nanoparticles2006In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 296, no 1, p. 71-78Article in journal (Refereed)
    Abstract [en]

      Nanocrystalline TiO2 powders of the rutile polymorph, synthesized by a sol–gel method, were treated with water solutions containing, respectively, formic, acetic, and citric acid and glycine in order to study the adsorption properties of these organic species. The samples were characterized by FTIR, Raman, powder XRD, and TEM. It was found that HCOOH, CH3COOH and HOC(COOH)(CH2COOH)2—but not NH2CH2COOH—adsorbed onto TiO2. The adsorption of HCOOH, CH3COOH and NH2CH2COOH onto the (110) surface of rutile was also studied by quantum-chemical periodic density functional theory (DFT) calculations. The organic molecules were from the computations found to adsorb strongly to the surfaces in a bridge-coordinating mode, where the two oxygens of the deprotonated carboxylic acid bind to two surface titanium ions. Surface relaxation is found to influence adsorption geometries and energies significantly. The results from DFT calculations and ab initio molecular-dynamics simulations of formic acid adsorption onto TiO2 are compared and match well with the experimental IR measurements, supporting the bridge-binding geometry of carboxylic-acid adsorption on the TiO2 nanoparticles.

  • 79.
    Ojamäe, Lars
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Pisani, C
    Theoretical characterization of divacancies at the surface and in bulk MgO1998In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 109, no 24, p. 10984-10995Article in journal (Refereed)
    Abstract [en]

    Two types of divacancy at the (001) surface of MgO are theoretically studied and compared with the corresponding defect in the bulk: the pit, where a surface magnesium and the oxygen ion underneath are removed, and the tub, where both removed ions are at the surface. All calculations have been performed by means of the EMBED program which adopts an embedded-cluster approach in the frame of the Hartree-Fock (HF) approximation [C. Pisani F. Corà, R. Nada, and R. Orlando, Comput. Phys. Commun. 82, 139 (1994); C. Pisani and U. Birkenheuer, ibid. 96, 152 (1996)]; the semi-infinite host crystal for the study of the surface defects has been simulated with a four-layer slab. The energy released on formation of the divacancy from the two charged isolated vacancies is very high, almost 300 kcal/mol. The tub divacancy is the most stable, both as a neutral and as a singly charged defect. For the paramagnetic center (one electron trapped in the cavity), spin density data are provided and discussed with reference to results from electron paramagnetic resonance experiments and molecular cluster calculations [E. Giamello M. C. Paganini, D. Murphy, A. M. Ferrari, and G. Pacchioni, J. Phys. Chem. 101, 971 (1997)]. It is suggested that the tub divacancy is a common defect, if not the most common, at the highly dehydrated MgO surface.

  • 80.
    Ojamäe, Lars
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Shavitt, Isaiah
    Ohio State Univ, Dept Chem, Columbus.
    Singer, Sherwin J
    Ohio State Univ, Dept Chem, Columbus.
    Potential models for simulations of the solvated proton in water1998In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 109, no 13, p. 5547-5564Article in journal (Refereed)
    Abstract [en]

    Analytical potential models are designed for simulations of water with excess protons. The potentials describe both intramolecular and intermolecular interactions, and allow dissociation and formation of the species (H 2 O) n H + . The potentials are parametrized in the form of interactions between H + and O 2− ions, with additional three-body (H–O–H) interaction terms and self-consistent treatment of the polarizability of the oxygen ions. The screening of electrostatic interactions caused by the overlap of the electron clouds in the real molecules is modeled by functions modifying the electric field at short distances. The model was derived by fitting to the potential surface of the H 5 O + 2 ion and other species, as obtained from ab initio MP2 calculations employing an extensive basis set. Emphasis was put on modeling the potential-energy surface for the proton-transfer reaction. Potential-surface profiles, geometry-optimizedstructures and formation energies of H 5 O + 2 , protonated water clusters [H + (H 2 O) n , n=2–4] and water clusters [(H 2 O) n , n=1–6] using these potentials are presented and compared to results using quantum-chemical calculations. The potential models can well reproduce ab initio results for the H 5 O + 2 ion, and can provide formation energies and structures of both protonated-water and water-only clusters that agree favorably with ab initio MP2 calculations.

  • 81.
    Ojamäe, Lars
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    SHAVITT, Isaiha
    Department of Chemistry, The Ohio State University.
    SINGER, Sherwin J.
    Department of Chemistry, The Ohio State University.
    POTENTIAL-ENERGY SURFACES AND VIBRATIONAL-SPECTRA OF H5O2+ AND LARGER HYDRATED PROTON COMPLEXES1995In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 56, no 29, p. 657-668Article in journal (Refereed)
    Abstract [en]

    This article presents calculations of the structure, binding energetics, potential energy surfaces, and vibrational spectra of the H5O ion. The 15-dimensional potential energy surface for the seven nuclei in the ionic complex was computed by pointwise ab initio Møller-Plesset second-order perturbation (MP2) calculations, using the correlation-consistent pVTZ basis set augmented with diffuse basis functions on oxygen. The potential energy surface for the proton-transfer mechanism was investigated, and the effects of surrounding water molecules on the proton-transfer potential energy curve was studied. Density functional calculations for the proton-transfer potential surface are compared to the MP2 results. Geometry-optimized structures, binding energies, and harmonic vibrational spectra of H5O and H9O are presented. The energy-minimum structure of H5O using the augmented pVTZ basis set is of C2 symmetry, whereas for H9O, using the TZ2P basis set, it is of C3 symmetry. The H-bonded OH stretching harmonic frequency of H5O is very low, 913 cm−1, whereas for H9O it is 2927 cm−1. The subspace spanned by the hydrogen-bonded OH distance and the OO distance were used in one- and two-dimensional calculations of the anharmonic vibrational spectrum using collocation methods. The coupling of the OH stretch with the OO vibration causes a redshift and the anharmonicity a blueshift of the OH frequency: the resulting fundamental frequency of the H-bonded OH vibration is 1275 cm−1. Zero-point energies of the proton vibration and pathways for exchange of protons within H5O are discussed. © 1995 John Wiley & Sons, Inc.

  • 82.
    Pedersen, Henrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lin, Ching-Chi
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    On the change of preferential growth orientation in chemical vapor deposition of titanium carbide by aromatic hydrocarbon precursors2013In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 31, no 2Article in journal (Refereed)
    Abstract [en]

    Thin films of titanium carbide grown by chemical vapor deposition exhibit a strong preferential (111) growth direction if aromatic hydrocarbons, such as benzene, are used as a carbon precursor. If aliphatic hydrocarbons such as methane are used, growth on the (100) surface is preferred. In this study, quantum chemical computations are used to study the adsorption of benzene and methane on the (100) and (111) surfaces to provide an explanation for the changed growth behavior. The adsorption energy of benzene is found to be approximately twice as high on the (111) surface as compared to the (100) surface, and adsorption studies further suggest that benzene chemisorbs on the (111) surface, while it physisorbs on the (100) surface. The studies reveal no significant differences in adsorption energy or behavior for methane on the two surfaces. The authors propose that the higher benzene adsorption energy and different adsorption behavior on the (111) surface are the explanations for the preferential growth orientation.

  • 83.
    Pedersen, Henrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Towards Biocompatibility of RE2O3 Nanocrystals − Water and Organic Molecules Chemisorbed on Gd2O3 and Y2O3 Nanocrystals Studied by Quantum-Chemical Computations2006In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 6, no 9, p. 2004-2008Article in journal (Refereed)
    Abstract [en]

    Nanocrystals of Gd2O3/Y2O3 and their interaction with water, formic acid, diethylene glycol (DEG), and tetramethoxy silane (TMOS) have been studied by quantum-chemical calculations at the B3LYP level using solvent-coated clusters of gadolinia and yttria. Adsorption energies, surface geometries, electronic structures, and excitation spectra were calculated. The results concerning adsorption strengths and superparamagnetic high-spin states can provide insight into the design of molecular-capped RE2O3 nanocrystals to be used in vivo.

  • 84.
    Pedersen, Henrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Söderlind, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Petoral, Rodrigo M.
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics. Linköping University, The Institute of Technology.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics. Linköping University, The Institute of Technology.
    Käll, Per-Olov
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    Surface interactions between Y2O3 nanocrystals and organic molecules—an experimental and quantum-chemical study2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 592, no 1-3, p. 124-140Article in journal (Refereed)
    Abstract [en]

    The surface interactions between Y2O3 nanocrystals and the organic molecules formic acid, diethylene glycol (DEG), and tetramethoxy silane (TMOS), have been studied experimentally and by quantum chemical calculations with the intent to elucidate the chemisorption characteristics such as adsorbate vibrational spectra and adsorption structures. Nanocrystal synthesis was performed by a colloidal method based on polyols and by a rapid combustion method. The products were experimentally characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS).

    In the quantum chemical calculations, the B3LYP hybrid density functional ab initio method was used to study the chemisorption of formic acid, DEG and TMOS at the surface of Y12O18 clusters. From a comparison of calculated and experimental vibrational spectra, the binding mode for formic acid on Y2O3 was inferred to be of bridge or bidentate type. The XPS and FT-IR experiments showed that DEG is chemisorbed on the particle surface. The experimental IR spectra of DEG chemisorbed on Y2O3 were consistent with an adsorption mode where the hydroxyl groups are deprotonated according to the quantum-chemical computations. The adsorption energy is of the order of 370 kJ mol−1 for formic acid, 550 kJ mol−1 for DEG, and 60 kJ mol−1 for TMOS, according to the quantum chemical calculations.

  • 85.
    Persson, P.
    et al.
    Department of Quantum Chemistry, Uppsala University, P.O. Box 518, SE-751 20 Uppsala, Sweden.
    Lunell, S.
    Department of Quantum Chemistry, Uppsala University, P.O. Box 518, SE-751 20 Uppsala, Sweden.
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Electronic interactions between aromatic adsorbates and metal oxide substrates calculated from first principles2002In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 364, no 5-6, p. 469-474Article in journal (Refereed)
    Abstract [en]

    The electronic structure of interfaces between aromatic adsorbates and metal oxide surfaces has been investigated using periodic hybrid ab initio Hartree-Fock-density functional theory calculations. Strong interfacial electronic coupling is observed for isonicotinic acid adsorbed on ZnO(1 0 1¯ 0) and TiO2(1 1 0) surfaces. The results are in good agreement with experiments of ultrafast surface electron transfer processes for TiO2, and current experimental controversies regarding ZnO are clarified theoretically. © 2002 Elsevier Science B.V. All rights reserved.

  • 86. Persson, P
    et al.
    Lunell, S
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Quantum chemical prediction of the adsorption conformations and dynamics at HCOOH-covered ZnO(10(1)over-bar-0) surfaces2002In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 89, no 3, p. 172-180Article in journal (Refereed)
    Abstract [en]

    Results from ab initio Hariree-Fock and gradient-corrected density functional theory calculations of formic acid interactions with ZnO (1010) surfaces are reported. Surface relaxation is found to affect equilibrium geometries and adsorption energies significantly. Large variations in adsorption energy with coverage and ordering of the adsorbates are revealed and explained in terms of strong and highly anisotropic electrostatic adsorbate-adsorbate interactions. The results are compared to published experimental and theoretical results, and differences in suggested binding geometries from the different studies are discussed. Dynamic properties of the adsorption, surface mobility, and surface reactivity are inferred from key elements of the potential energy surface obtained from the quantum chemical computations and supported by ab initio molecular dynamics simulations. (C) 2002 Wiley Periodicals, Inc.

  • 87.
    Persson, P
    et al.
    Uppsala universitet, Institutionen för kvantkemi.
    Ojamae, L
    Periodic Hartree-Fock study of the adsorption of formic acid on ZnO(10(1)over-bar-0)2000In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 321, no 3-4, p. 302-308Article in journal (Refereed)
    Abstract [en]

    Adsorption of formic acid (HCOOH) on ZnO(10 (1) over bar 0) surfaces has been investigated by means of quantum-chemical ab initio periodic Hartree-Fock calculations. One 'bridging' structure, characterized by a formate anion symmetrically bonded via its t

  • 88.
    Persson, Petter
    et al.
    Department of Quantum Chemistry, Uppsala University.
    Bergström, Robert
    Department of Quantum Chemistry, Uppsala University.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    Lunell, Sten
    Department of Quantum Chemistry, Uppsala University.
    Quantum-chemical studies of metal oxides for photoelectrochemical applications2002In: Advances in quantum chemistry.: Volume 41, A tribute to the life and work of Per-Olov Löwdin / [ed] John R Sabin; Erkki Brändas; Per Olov Löwdin, USA: Elsevier Science , 2002, 1, p. 203-263Chapter in book (Other academic)
    Abstract [en]

    A review of recent research, as well as new results, are presented on transition metal oxide clusters, surfaces, and crystals. Quantum-chemical calculations of clusters of first row transition metal oxides have been made to evaluate the accuracy of ab initio and density functional calculations. Adsorbates on metal oxide surfaces have been studied with both ab initio and semi-empirical methods, and results are presented for the bonding and electronic interactions of large organic adsorbates, e.g. aromatic molecules, on Ti02 and ZnO. Defects and intercalation, notably of H, Li, and Na in Ti02 have been investigated theoretically. Comparisons with experiments are made throughout to validate the calculations. Finally, the role of quantum-chemical calculations in the study of metal oxide based photoelectrochemical devices, such as dyesensitized solar cells and electrochromic displays. is discussed.

  • 89.
    Pettersson, Lars G. M.
    et al.
    FYSIKUM, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden.
    Nilsson, Anders
    Physics Department, University of Uppsala, Box 530, S-751 21 Uppsala, Sweden.
    Myneni, Satish
    Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
    Luo, Yi
    FYSIKUM, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden.
    Nyberg, Mats
    FYSIKUM, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden.
    Cavalleri, Matteo
    FYSIKUM, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Näslund, Lars-Åke
    FYSIKUM, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden.
    Ogasawara, Hirohito
    Physics Department, University of Uppsala, Box 530, S-751 21 Uppsala, Sweden.
    Odelius, Michael
    Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
    Pelmenschikov, Alexander
    FYSIKUM, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden.
    Electronic structure effects from hydrogen bonding in the liquid phase and in chemisorption: an integrated theory and experimental effort2001In: Journal of Synchrotron Radiation, ISSN 0909-0495, E-ISSN 1600-5775, Vol. 8, no 2, p. 136-140Article in journal (Refereed)
    Abstract [en]

    A closely integrated theoretical and experimental effort to understand chemical bonding using X-ray spectroscopic probes is presented. Theoretical techniques to simulate XAS (X-ray absorption spectroscopy), XES (X-ray emission spectroscopy), RIXS (resonant inelastic X-ray scattering) and XPS (X-ray photoelectron spectroscopy) spectra have been developed and implemented within a density functional theory (DFT) framework. In combination with new experimental techniques, such as high-resolution XAS on liquid water under ambient conditions and XES on complicated surface adsorbates, new insight into e.g. hydrogen-bonded systems is obtained. For the (3×2) overlayer structure of glycine/Cu(110), earlier work has been extended to include adsorbate-adsorbate interactions. Structures are optimized for large cluster models and for periodic boundary conditions. It is found that specific features in the spectra arise from hydrogen-bonding interactions, which thus have important effects at the molecular-orbital level. XAS on liquid water shows a pronounced pre-edge feature with significant intensity, while the spectrum of ice shows only little intensity in this region. Theoretical spectrum calculations, based on instantaneous structures obtained from molecular-dynamics (MD) simulations, show that the pre-edge feature in the liquid is caused by water molecules with unsaturated hydrogen bonding. Some aspects of the theoretical simulations will be briefly discussed.

  • 90.
    Rouf, Polla
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    O´brien, Nathan
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Rönnby, Karl
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Samii, Rouzbeh
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 42, p. 25691-25700Article in journal (Refereed)
    Abstract [en]

    Indium nitride (InN) is an interesting material for future high-frequency electronics due to its high electron mobility. The problematic deposition of InN films currently prevents full exploration of InN-based electronics. We present studies of atomic layer deposition (ALD) of InN using In precursors with bidentate ligands forming In-N bonds: tris(N,N-dimethyl-N,N -diisopropylguanidinato)indium(III), tris(N,N-diisopropylamidinato)indium(III), and tris(N,N-diisopropylformamidinato)indium(III). These compounds form a series were the size of the substituent on the endocyclic position decreases from -NMe2 to -Me and to -H, respectively. We show that when the size of the substituent decreases, the InN films deposited have a better crystalline quality, of better optical quality, lower roughness, and an In/N ratio closer to unity. From quantum chemical calculations, we show that the smaller substituents lead to less steric repulsion and weaker bonds between the ligand and In center. We propose that these effects render a more favored surface chemistry for the nitridation step in the ALD cycle, which explains the improved film properties.

    The full text will be freely available from 2020-09-26 14:43
  • 91. Roy, S
    et al.
    Salomonsson, Anette
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Aulin, C
    Käll, Per-Olov
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Strand, M
    Sanati, M
    Metal oxide nanoparticles as novel gate materials for field-effect gas sensors2006In: Materials and Manufacturing Processes, ISSN 1042-6914, E-ISSN 1532-2475, Vol. 21, p. 275-278Article in journal (Refereed)
    Abstract [en]

      

  • 92.
    Rönnby, Karl
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Buttera, Sydney C.
    Carleton Univ, Canada.
    Rouf, Polla
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Barry, Sean T.
    Carleton Univ, Canada.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Methylamines as Nitrogen Precursors in Chemical Vapor Deposition of Gallium Nitride2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 11, p. 6701-6710Article in journal (Refereed)
    Abstract [en]

    Chemical vapor deposition (CVD) is one of the most important techniques for depositing thin films of the group 13 nitrides (13-Ns), AIN, GaN, InN, and their alloys, for electronic device applications. The standard CVD chemistry for 13-Ns uses ammonia as the nitrogen precursor; however, this gives an inefficient CVD chemistry, forcing N/13 ratios of 100/1 or more. Here, we investigate the hypothesis that replacing the N-H bonds in ammonia with weaker N-C bonds in methylamines will permit better CVD chemistry, allowing lower CVD temperatures and an improved N/13 ratio. Quantum chemical computations show that while the methylamines have a more reactive gas-phase chemistry, ammonia has a more reactive surface chemistry. CVD experiments using methylamines failed to deposit a continuous film, while instead micrometer-sized gallium droplets were deposited. This study shows that the nitrogen surface chemistry is most likely more important to be considered than the gas-phase chemistry when searching for better nitrogen precursors for 13-N CVD.

    The full text will be freely available from 2020-02-28 08:58
  • 93.
    Salomonsson, Anette
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Petoral Jr., Rodrigo M.
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
    Aulin, Christian
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Käll, Per-Olov
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
    Strand, Michael
    School of Technology and Design/Chemistry, Växjö University, Växjö, Sweden.
    Sanati, Mehri
    School of Technology and Design/Chemistry, Växjö University, Växjö, Sweden.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Nanocrystalline Ruthenium oxide and Ruthenium in sensing applications -an experimental and theoretical study2006In: Journal of Nanoparticle Research, ISSN 1388-0764, Vol. 8, no 6, p. 899-910Article in journal (Refereed)
    Abstract [en]

    In this project, we have explored RuO2 and Ru nanoparticles (∼ ∼10 and ∼ ∼5 nm, respectively, estimated from XRD data) to be used as gate material in field effect sensor devices. The particles were synthesized by wet chemical procedure. The capacitance versus voltage characteristics of the studied capacitance shifts to a lower voltage while exposed to reducing gases. The main objectives are to improve the selectivity of the FET sensors by tailoring the dimension and surface chemistry of the nanoparticles and to improve the high temperature stability. The sensors were characterized using capacitance versus voltage measurements, at different frequencies, 500 Hz to 1 MHz, and temperatures at 100–400°C. The sensor response patterns have been found to depend on operating temperature. X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the oxidation state due to gas exposure. Quantum-chemical computations suggest that heterolytic dissociative adsorption is favored and preliminary computations regarding water formation from adsorbed hydrogen and oxygen was also performed.

  • 94.
    Salomonsson, Anette
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Roy, S
    Aulin, C
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Käll, Per-Olov
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Strand, M
    Sanati, M
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    RuO2 and Ru nanoparticles for MISiCFET gas sensors2005In: Nanotech NSTI 2005,2005, 2005, p. 269-Conference paper (Refereed)
  • 95.
    Salomonsson, Anette
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Roy, Somenath
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Aulin, Christian
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Cerdà, Judith
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Käll, Per-Olov
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
    Strand, Michael
    Division of Chemistry, Växjö University, Växjö, Sweden.
    Sanati, Mehri
    Division of Chemistry, Växjö University, Växjö, Sweden.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Nanoparticles for long-term stable, more selective MISiCFET gas sensors2005In: Sensors and Actuators B, ISSN 0925-4005, Vol. 107, no 2, p. 831-838Article in journal (Refereed)
    Abstract [en]

    Synthesis of metal-oxide nanoparticles and utilization of these particles as gate materials for field-effect sensor devices is reported. Improved selectivity to specific gases is expected by modulating the size of the oxide nanoparticles or impregnating them with catalytic metals. Another objective is to improve the long-term thermal stability of the sensors, since the metal loaded nanoparticles may prevent thermally induced restructuring of the gate layer, which is often a problematic issue for the catalytic metal layers. Because of its reasonably high electrical conductivity, which is especially important for the capacitive gas sensors, ruthenium dioxide has been identified to be one of the potential candidates as gate material for the field-effect sensor devices. Interestingly, this material has been found to change its resistivity in different gaseous ambients. When used as a gate material, sensitivity to reducing gases has been observed for the RuO2/SiO2/4H-SiC capacitors. Changes in the resistivity of the films due to various gas exposures have also been recorded. Morphological studies of nanoparticles (SiO2 and Al2O3), loaded or impregnated with catalytic metals (e.g. Pt), have been performed.

  • 96.
    Salomonsson, Anette
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Roy, Somenath
    Aulin, Christian
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
    Käll, Per-Olov
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
    Strand, Michael
    Växjö university.
    Sanati, Mehri
    Växjö university.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Ruthenium dioxide & Ru Nanoparticles for MISiCFET gas sensors2005In: Nanotech 2005 (NSTI) Anaheim, USA, 8-12 May, 2005, Vol. 2, no Chapter 4, p. 269–272-Conference paper (Refereed)
    Abstract [en]

    Catalytically active nanoparticles used as gate material on SiC-FET gas sensors. The goal is to improve the selsectivity and senstitivty.The sensors are sensitive towards oxidising and reducing gases (H2, NH3, C3H6).

  • 97.
    Singer, S. J.
    et al.
    Ohio State Univ, Dept Chem, Columbus, OH 43210 USA.
    Knight, C. J.
    Ohio State Univ, Dept Chem, Columbus, OH 43210 USA.
    Kuo, J. L.
    Univ Penn, Ctr Mol Modeling, Dept Chem, Philadelphia, PA 19104 USA.
    Hirsch, T. K.
    Univ Stockholm, Arrhenius Lab, S-10691 Stockholm, Sweden.
    Ojamäe, L.
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Klein, M. L.
    Univ Penn, Ctr Mol Modeling, Dept Chem, Philadelphia, PA 19104 USA.
    Hydrogen bond topology and proton ordering phase transitions in ice2005Conference paper (Other academic)
  • 98.
    Singer, S J
    et al.
    Ohio State Univ, Dept Chem, Columbus, OH 43210 USA.
    McDonald, S
    Ohio State Univ, Dept Chem, Columbus, OH 43210 USA.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Topology versus temperature: Thermal behavior of H+(H2O)(8) and H+(H2O)(16)2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 112, no 2, p. 710-716Article in journal (Refereed)
    Abstract [en]

    Monte Carlo simulations based on the OSS2 potential indicate the structure of the small protonated water clusters, H + (H 2 O) 8 and H + (H 2 O) 16 , is far from what could be expected for the proton solvated in bulk water. Near room temperature we find H + (H 2 O) n , n=8,16 clusters have a treelike topology with chains of waters emanating from a central H 3 O + moiety. Only at lower temperatures do cycles and cages of water appear. These findings bear upon experiments in a variety of disciplines.

  • 99. Singer, S.J
    et al.
    Kuo, J-L
    Hirsch, T.K
    Knight, C
    Ojamäe, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry.
    Klein, M.L.
    Hydrogen-bond topology and the ice VII/VIII and ice Ih/XI proton-ordering phase transitions,2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, p. 135701-135701Article in journal (Refereed)
  • 100.
    Stenberg, Pontus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Erdtman, Edvin
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Matching precursor kinetics to afford a more robust CVD chemistry: a case study of the C chemistry for silicon carbide using SiF4 as Si precursor2017In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 5, p. 5818-5823Article in journal (Refereed)
    Abstract [en]

    Chemical Vapor Deposition (CVD) is one of the technology platforms forming the backbone of the semiconductor industry and is vital in the production of electronic devices. To upscale a CVD process from the lab to the fab, large area uniformity and high run-to-run reproducibility are needed. We show by a combination of experiments and gas phase kinetics modeling that the combinations of Si and C precursors with the most well-matched gas phase chemistry kinetics gives the largest area of of homoepitaxial growth of SiC. Comparing CH4, C2H4 and C3H8 as carbon precursors to the SiF4 silicon precursor, CH4 with the slowest kinetics renders the most robust CVD chemistry with large area epitaxial growth and low temperature sensitivity. We further show by quantum chemical modeling how the surface chemistry is impeded by the presence of F in the system which limits the amount of available surface sites for the C to adsorb.

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