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  • 1.
    Huang, C
    et al.
    Stanford Synchrotron Radiat Lightsource.
    Wikfeldt, K T
    Stockholm University.
    Tokushima, T
    RIKEN SPring 8, Mikazuki, Hyogo, Japan .
    Nordlund, D
    Stanford Synchrotron Radiat Lightsource.
    Harada, Y
    RIKEN SPring 8, Mikazuki, Hyogo Japan .
    Bergmann, U
    Stanford Synchrotron Radiat Lightsource.
    Niebuhr, M
    Stanford Synchrotron Radiat Lightsource.
    Weiss, T M
    Stanford Synchrotron Radiat Lightsource.
    Horikawa, Y
    RIKEN SPring 8, Mikazuki, Hyogo Japan .
    Leetmaa, M
    Stockholm University.
    Ljungberg, M P
    Stockholm University.
    Takahashi, O
    Hiroshima University.
    Lenz, Annika
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Lyubartsev, A P
    Stockholm University.
    Shin, S
    RIKEN SPring 8, Mikazuki, Hyogo Japan .
    Pettersson, L G M
    Stockholm University.
    Nilsson, A
    Stanford Synchrotron Radiat Lightsource.
    Letter: Reply to Soper et al.: Fluctuations in water around a bimodal distribution of local hydrogen-bonded structural motifs2010Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 12, s. E45-E45Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    n/a

  • 2.
    Huang, C
    et al.
    Stanford Synchrotron Radiat Lightsource.
    Wikfeldt, K T
    AlbaNova.
    Tokushima, T
    RIKEN.
    Nordlund, D
    Stanford Synchrotron Radiat Lightsource.
    Harada, Y
    RIKEN.
    Bergmann, U
    Stanford Synchrotron Radiat Lightsource.
    Niebuhr, M
    Stanford Synchrotron Radiat Lightsource.
    Weiss, T M
    Stanford Synchrotron Radiat Lightsource.
    Horikawa, Y
    RIKEN.
    Leetmaa, M
    AlbaNova.
    Ljungberg, M P
    AlbaNova.
    Takahashi, O
    Hiroshima University.
    Lenz, Annika
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Lyubartsev, A P
    Stockholm University.
    Shin, S
    RIKEN.
    Pettersson, L G M
    AlbaNova.
    Nilsson, A
    Stanford Synchrotron Radiat Lightsource.
    The inhomogeneous structure of water at ambient conditions2009Ingår i: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, ISSN 0027-8424, Vol. 106, nr 36, s. 15214-15218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Small-angle X-ray scattering (SAXS) is used to demonstrate the presence of density fluctuations in ambient water on a physical length-scale of approximate to 1 nm; this is retained with decreasing temperature while the magnitude is enhanced. In contrast, the magnitude of fluctuations in a normal liquid, such as CCl4, exhibits no enhancement with decreasing temperature, as is also the case for water from molecular dynamics simulations under ambient conditions. Based on X-ray emission spectroscopy and X-ray Raman scattering data we propose that the density difference contrast in SAXS is due to fluctuations between tetrahedral-like and hydrogen-bond distorted structures related to, respectively, low and high density water. We combine our experimental observations to propose a model of water as a temperature-dependent, fluctuating equilibrium between the two types of local structures driven by incommensurate requirements for minimizing enthalpy (strong near-tetrahedral hydrogen-bonds) and maximizing entropy (non-directional H-bonds and disorder). The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.

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    FULLTEXT01
  • 3. Beställ onlineKöp publikationen >>
    Lenz, Annika
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Theoretical Investigations of Water Clusters, Ice Clathrates and Functionalized Nanoparticles2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Nanosized structures are of intermediate size between individual molecules and bulkmaterials which gives them several unique properties. At the same time their relative limitedsizes make them suitable for studies by the methods of computational chemistry. In this thesiswater clusters, ice clathrates and functionalized metal-oxide nanoparticles have been studiedby quantum-chemical calculations and statistical thermodynamics.

    The stabilities of water clusters composed of up to 100 molecules have been investigated. Themultitude of possible H-bonded topologies and their importance for determining theproperties of the clusters have been highlighted. Several structural characteristics of thehydrogen bonded network have been examined and the structural factors that determine thestability of an H-bonded network have been identified. The stability of two kinds of oxygenframeworks for water clusters have been analyzed, taking into account thermal energy andentropy corrections. Clusters with many 4-coordinated molecules have been found to be lowerin energy at low temperatures whereas the clusters with less-coordinated molecules dominateat higher temperatures. The equilibrium size distribution of water clusters as a function oftemperature and pressure has been computed using statistical thermodynamics. Themicroscopic local structure of liquid water has been probed by utilizing information from thestudied water clusters. The average number of H-bonds in liquid water has been predicted byfitting calculated average IR spectra for different coordination types in water clusters toexperimental IR spectra.

    Water can form an ice-like structure that encloses various molecules such as methane. Thesemethane hydrates are found naturally at the ocean floor and in permafrost regions and canconstitute a large unemployed energy resource as well as a source of an effective green-housegas. The pressure dependencies of the crystal structures, lattice energies and phase transitionsfor the three methane hydrates with the clathrate structures I, II and H have been mapped out.

    Zinc oxide is a semiconducting material with interesting luminescence properties that can beutilized in optical devices, such as photodetectors, light emitting devices and biomarkers. Theeffect of water molecules adsorbed on the ZnO surface when adsorbing organic acids havebeen investigated. Changes in optical properties by the adsorption of carboxylic acids havebeen studied and compared with experimental results. Aromatic alcohols at TiO2 metal-oxidenanoparticles have been studied as model systems for dye-sensitizied solar cells. Adsorptiongeometries are predicted and the influence from the adsorbed molecules on the electronicproperties has been studied.

    Delarbeten
    1. A theoretical study of water clusters: the relation between hydrogen-bond topology and interaction energy from quantum-chemical computations for clusters with up to 22 molecules
    Öppna denna publikation i ny flik eller fönster >>A theoretical study of water clusters: the relation between hydrogen-bond topology and interaction energy from quantum-chemical computations for clusters with up to 22 molecules
    2005 (Engelska)Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, s. 1905-1911Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Quantum-chemical calculations of a variety of water clusters with eight, ten and twelve molecules were performed, as well as for selected clusters with up to 22 water molecules. Geometry optimizations were carried out at the B3LYP/cc-pVDZ level and single-point energies were calculated at the B3LYP/aug-cc-pVDZ level for selected clusters. The electronic energies were studied with respect to the geometry of the oxygen arrangement and six different characteristics of the hydrogen-bond arrangement in the cluster. Especially the effect of the placement of the non-hydrogen bonding hydrogens on the interaction energy was studied. Models for the interaction energy with respect to different characteristics of the hydrogen-bond arrangement were derived through least-square fits. The results from the study of the clusters with eight, ten and twelve molecules are used to predict possible low-energy structures for various shapes of clusters with up to 22 molecules.

    Ort, förlag, år, upplaga, sidor
    RCS Publishing, 2005
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-30387 (URN)10.1039/b502109j (DOI)15935 (Lokalt ID)15935 (Arkivnummer)15935 (OAI)
    Tillgänglig från: 2009-10-09 Skapad: 2009-10-09 Senast uppdaterad: 2017-12-13
    2. On the stability of dense versus cage-shaped water clusters: quantum-chemical investigations of zero-point energies, free energies, basis-set effects and IR spectra of (H2O)12 and (H2O)20
    Öppna denna publikation i ny flik eller fönster >>On the stability of dense versus cage-shaped water clusters: quantum-chemical investigations of zero-point energies, free energies, basis-set effects and IR spectra of (H2O)12 and (H2O)20
    2006 (Engelska)Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 418, s. 361-367Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The energetics of water clusters with 12 and 20 molecules are studied by quantum-chemical computations using the B3LYP, MP2, MP4 and CCSD methods. The effect of electron-correlation method, basis set, zero-point energy, thermal energy and Gibbs free energy on the relative stability of fused clusters (structures consisting of cubic- or prismatic-shaped subparts) versus cage-shaped clusters (more open structures with only three-coordinated molecules) are investigated. The O–H stretching IR vibrational spectra are studied. The contribution of zero-point and Gibbs free energy will diminish the energy difference between fused- and cage-shaped clusters, but the fused structures are still slightly more favorable.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-36194 (URN)10.1016/j.cplett.2005.11.013 (DOI)30469 (Lokalt ID)30469 (Arkivnummer)30469 (OAI)
    Tillgänglig från: 2009-10-10 Skapad: 2009-10-10 Senast uppdaterad: 2017-12-13
    3. Theoretical IR spectra for water clusters (H2O)n (n = 6-22, 28, 30) and identification of spectral contributions from different H-Bond conformations in gaseous and liquid water
    Öppna denna publikation i ny flik eller fönster >>Theoretical IR spectra for water clusters (H2O)n (n = 6-22, 28, 30) and identification of spectral contributions from different H-Bond conformations in gaseous and liquid water
    2006 (Engelska)Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 110, nr 50, s. 13388-13393Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The vibrational IR spectra in the O-H stretching region are computed for water clusters containing 6-22, 28, and 30 molecules using quantum-chemical calculations (B3LYP and an augmented basis set). For the cluster with 20 molecules, several different structures were studied. The vibrational spectrum was partitioned into contributions from different molecules according to their coordination properties. The frequency shifts depend on the number of donated/accepted H-bonds primarily of the two molecules participating in the H-bond, but also of the surrounding molecules H-bonding to these molecules. The frequencies of H-bonds between two molecules of the same coordination type are spread over a broad interval. The most downshifted hydrogen-bond vibrations are those donated by a single-donor 3-coordinated molecule where the H-bond is accepted by a single-acceptor molecule. The H-bonded neighbors influence the downshift, and their contribution can be rationalized in the same way as for the central dimer. Single donors/acceptors cause larger downshifts than 4-coordinated molecules, and the least downshift is obtained for double donors/acceptors. This result is at variance with the conception that experimental liquid water spectra may be divided into components for which larger downshifts imply higher H-bond coordination. A mean spectral contribution for each coordination type for the donor molecule was derived and fitted to the experimental liquid water IR spectrum, which enabled an estimation of the distribution of H-bond types and average number of H-bonds (3.0 ± 0.2) in the liquid. © 2006 American Chemical Society.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-36614 (URN)10.1021/jp066372x (DOI)31825 (Lokalt ID)31825 (Arkivnummer)31825 (OAI)
    Tillgänglig från: 2009-10-10 Skapad: 2009-10-10 Senast uppdaterad: 2017-12-13
    4. A theoretical study of water equilibria: The cluster distribution versus temperature and pressure for (H2O)n, n=1–60, and ice
    Öppna denna publikation i ny flik eller fönster >>A theoretical study of water equilibria: The cluster distribution versus temperature and pressure for (H2O)n, n=1–60, and ice
    2009 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 13, s. 134302-134302-13Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The size distribution of water clusters at equilibrium is studied using quantum-chemical calculations in combination with statistical thermodynamics. The necessary energetic data is obtained by quantum-chemical B3LYP computations and through extrapolations from the B3LYP results for the larger clusters. Clusters with up to 60 molecules are included in the equilibrium computations. Populations of different cluster sizes are calculated using both an ideal gas model with noninteracting clusters and a model where a correction for the interaction energy is included analogous to the van der Waals law. In standard vapor the majority of the water molecules are monomers. For the ideal gas model at 1 atm large clusters [56-mer (0–120 K) and 28-mer (100–260 K)] dominate at low temperatures and separate to smaller clusters [21–22-mer (170–280 K) and 4–6-mer (270–320 K) and to monomers (300–350 K)] when the temperature is increased. At lower pressure the transition from clusters to monomers lies at lower temperatures and fewer cluster sizes are formed. The computed size distribution exhibits enhanced peaks for the clusters consisting of 21 and 28 water molecules; these sizes are for protonated water clusters often referred to as magic numbers. If cluster-cluster interactions are included in the model the transition from clusters to monomers is sharper (i.e., occurs over a smaller temperature interval) than when the ideal-gas model is used. Clusters with 20–22 molecules dominate in the liquid region. When a large icelike cluster is included it will dominate for temperatures up to 325 K for the noninteracting clusters model. Thermodynamic properties (Cp, H) were calculated with in general good agreement with experimental values for the solid and gas phase. A formula for the number of H-bond topologies in a given cluster structure is derived. For the 20-mer it is shown that the number of topologies contributes to making the population of dodecahedron-shaped cluster larger than that of a lower-energy fused prism cluster at high temperatures.

    Nyckelord
    water, vapour, ice, quantum chemistry, statistical thermodynamics, hydrogen bonding
    Nationell ämneskategori
    Teoretisk kemi
    Identifikatorer
    urn:nbn:se:liu:diva-50778 (URN)10.1063/1.3239474 (DOI)
    Tillgänglig från: 2009-10-14 Skapad: 2009-10-14 Senast uppdaterad: 2017-12-12
    5. Computational studies of the stability of the (H2O)100 nanodrop
    Öppna denna publikation i ny flik eller fönster >>Computational studies of the stability of the (H2O)100 nanodrop
    2010 (Engelska)Ingår i: Journal of Molecular Structure: THEOCHEM, ISSN 0166-1280, Vol. 944, nr 1-3, s. 163-167Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The stability of the (H2O)100 nanodrop, experimentally known from a polyoxomolybdatecrystal structure (Müller et al. Inorg. Chem. Commun., 2003, 6, 52) and other structuresinferred from clathrate structures, are studied by quantum-chemical B3LYP computations.The free energies are compared to the trends for smaller clusters with 15-30 molecules. Forthe small clusters both cage-based structures and denser structures with a larger number of Hbondsobtained by an evolutionary algorithm (Bandow and Hartke, J. Phys. Chem. A, 2006,110, 5809) are used. The dense structures are most often found to be lower in electronicenergy. The cage-based structures, to which the structure of the experimentally found(H2O)100 cluster can be categorized, become more stable when Gibbs free energy is calculatedat 298 K. Additional cage-based clusters in the 35-81 molecular range were constructed forcomparison. The experimental cluster with 100 molecules (C2h/Ci-symmetry for oxygens/allatoms) and the constructed cluster with 42 molecules are found to be lower in energy than aplausible overall trend. The (H2O)42 cluster has an extraordinary high symmetry (S6), evenwhen the hydrogens are considered. The (H2O)100 cluster is the only of the studied clusters forwhich ΔG is negative at 298 K.

    Nyckelord
    Water clusters, Quantum-chemical computations, Hydrogen bonding, B3LYP calculations, Gibbs free energy
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-53176 (URN)10.1016/j.theochem.2009.12.033 (DOI)000275688200022 ()
    Anmärkning
    Original Publication: Annika Lenz and Lars Ojamäe, Computational studies of the stability of the (H2O)100 nanodrop, 2010, Journal of Molecular Structure: THEOCHEM, (944), 1-3, 163-167. http://dx.doi.org/10.1016/j.theochem.2009.12.033 Copyright: Elsevier Science B.V., Amsterdam http://www.elsevier.com/ Tillgänglig från: 2010-01-18 Skapad: 2010-01-18 Senast uppdaterad: 2017-12-12
    6. Structures of the I-, II- and H-Methane Clathrates and the Ice−Methane Clathrate Phase Transition from Quantum-Chemical Modeling with Force-Field Thermal Corrections
    Öppna denna publikation i ny flik eller fönster >>Structures of the I-, II- and H-Methane Clathrates and the Ice−Methane Clathrate Phase Transition from Quantum-Chemical Modeling with Force-Field Thermal Corrections
    2011 (Engelska)Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, nr 23, s. 6169-6176Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Methane hydrates with the three clathrate structures I, II and H are studied by quantumchemicalmethods. The periodic B3LYP computations are combined with force-field methodsfor the thermal energy corrections. The pressure dependencies for the crystal structures, latticeenergies and guest molecule interactions are derived. Quantum-chemical geometryoptimizations predict too small cell volumes compared to experimental data, but includingzero-point energy and thermal energy the cell volume increases and the correct densities areobtained. Phase diagram for the three structures are investigated, and phase transitions werefound at 5 GPa for the MH-I–MH-II transition and at 10 GPa for the MH-II–MH-H transition.

    Ort, förlag, år, upplaga, sidor
    ACS Publications, 2011
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-53177 (URN)10.1021/jp111328v (DOI)
    Anmärkning
    The original title of this article was: "Structure and phase transitions of I-, II- and H- methane clathrates and ice from quantum-chemical B3LYP computations with corrections for thermal effects".Tillgänglig från: 2010-01-18 Skapad: 2010-01-18 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
    7. ZnO Nanoparticles Functionalized with Organic Acids: An Experimental and Quantum-Chemical Study
    Öppna denna publikation i ny flik eller fönster >>ZnO Nanoparticles Functionalized with Organic Acids: An Experimental and Quantum-Chemical Study
    Visa övriga...
    2009 (Engelska)Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 40, s. 17332-17341Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Electrochemical synthesis and physical characterization of ZnO nanoparticles functionalized with four different organic acids, three aromatic (benzoic, nicotinic, and trans-cinnamic acid) and one nonaromatic (formic acid), are reported. The functionalized nanoparticles have been characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV−vis, and photoluminescence spectroscopy. The adsorption of the organic acids at ZnO nanoparticles was further analyzed and interpreted using quantum-chemical density-functional theory computations. Successful functionalization of the nanoparticles was confirmed experimentally by the measured splitting of the carboxylic group stretching vibrations as well as by the N(1s) and C(1s) peaks from XPS. From a comparison between computed and experimental IR spectra, a bridging mode adsorption geometry was inferred. PL spectra exhibited a remarkably stronger near band edge emission for nanoparticles functionalized with formic acid as compared to the larger aromatic acids. From the quantum-chemical computations, this was interpreted to be due to the absence of aromatic adsorbate or surface states in the band gap of ZnO, caused by the formation of a complete monolayer of HCOOH. In the UV−vis spectra, strong charge-transfer transitions were observed.

    Nyckelord
    nanoparticles, ZnO, organic acids, adsorption, synthesis, XPS, UV-vis, quantum chemical calculations
    Nationell ämneskategori
    Fysikalisk kemi
    Identifikatorer
    urn:nbn:se:liu:diva-50783 (URN)10.1021/jp905481v (DOI)
    Tillgänglig från: 2009-10-14 Skapad: 2009-10-14 Senast uppdaterad: 2017-12-12
    8. Quantum-chemical investigations of phenol and larger aromatic molecules at the TiO2 anatase (101) surface
    Öppna denna publikation i ny flik eller fönster >>Quantum-chemical investigations of phenol and larger aromatic molecules at the TiO2 anatase (101) surface
    2008 (Engelska)Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 117, s. 012020-(8 pp)Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Adsorption of aromatic molecules at the (101) surface of titanium dioxide anatase is studied by quantum-chemical B3LYP computations, where both cluster and periodic calculations were performed and compared. For phenol different adsorption modes at a TiO2 cluster were mapped out and the energetically most favourable conformation was used for investigation of the electronic structure, for periodic calculations, and as a mould for the adsorption modes of phenylmethanol, phenylethanol, naphthalen-2-ol, phenanthren-2-ol, pyren-2-ol and perylen-2-ol. The alcohols form a H-bond to a surface O and a O(molecule)-Ti bond. For the larger aromatic molecules their increasingly higher HOMO levels decrease the effective bad gap of the system. Inclusion of spacer groups as in phenylmethanol and phenylethanol results in higher adsorption energies and larger band gaps. The LUMOs for the adsorbates help visualize the electronic coupling to the surface. Comparison of the cluster with the periodic model indicates that the former describes the electronic coupling in a similar manner as the latter, although the former lacks in the description of the anatase substrate.

    Nyckelord
    TiO2, anatase, phenol, adsorption, nanoparticles
    Nationell ämneskategori
    Teoretisk kemi
    Identifikatorer
    urn:nbn:se:liu:diva-50664 (URN)10.1088/1742-6596/117/1/012020 (DOI)
    Tillgänglig från: 2009-10-13 Skapad: 2009-10-13 Senast uppdaterad: 2017-12-12
    Ladda ner fulltext (pdf)
    Theoretical Investigations of Water Clusters, Ice Clathrates and Functionalized Nanoparticles
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    Cover
  • 4.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Kariis, Hans
    Swedish Defence Research Agency.
    Pohl, Anna
    Swedish Defence Research Agency.
    Persson, Petter
    Lund University.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    The electronic structure and reflectivity of PEDOT:PSS from density functional theory2011Ingår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 384, nr 03-jan, s. 44-51Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The geometric and electronic structure of condensed phase organic conducting polymer PEDOT:PSS blends has been investigated by periodic density functional theory (DFT) calculations with a generalized-gradient approximation (GGA) functional, and a plane wave basis set. The influence of the degree of doping of the PEDOT polymer on structural and optical parameters such as the reflectivity, absorbance, conductivity, dielectric function, refractive index and the energy-loss function is studied. A flip from the benzoid to the quinoid structure is observed in the calculations when the neutral PEDOT is doped by negatively charged PSS. Also the optical properties are affected by the doping. In particular, the reflectivity was found to be very sensitive to the degree of doping, where higher doping implies higher reflectivity. The reflectivity is highly anisotropic, with the dominant contribution stemming from the direction parallel to the PEDOT polymer chain.

    Ladda ner fulltext (pdf)
    fulltext
  • 5.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Karlsson, Maria
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Quantum-chemical investigations of phenol and larger aromatic molecules at the TiO2 anatase (101) surface2008Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 117, s. 012020-(8 pp)Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adsorption of aromatic molecules at the (101) surface of titanium dioxide anatase is studied by quantum-chemical B3LYP computations, where both cluster and periodic calculations were performed and compared. For phenol different adsorption modes at a TiO2 cluster were mapped out and the energetically most favourable conformation was used for investigation of the electronic structure, for periodic calculations, and as a mould for the adsorption modes of phenylmethanol, phenylethanol, naphthalen-2-ol, phenanthren-2-ol, pyren-2-ol and perylen-2-ol. The alcohols form a H-bond to a surface O and a O(molecule)-Ti bond. For the larger aromatic molecules their increasingly higher HOMO levels decrease the effective bad gap of the system. Inclusion of spacer groups as in phenylmethanol and phenylethanol results in higher adsorption energies and larger band gaps. The LUMOs for the adsorbates help visualize the electronic coupling to the surface. Comparison of the cluster with the periodic model indicates that the former describes the electronic coupling in a similar manner as the latter, although the former lacks in the description of the anatase substrate.

  • 6.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    A theoretical study of water clusters: the relation between hydrogen-bond topology and interaction energy from quantum-chemical computations for clusters with up to 22 molecules2005Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, s. 1905-1911Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum-chemical calculations of a variety of water clusters with eight, ten and twelve molecules were performed, as well as for selected clusters with up to 22 water molecules. Geometry optimizations were carried out at the B3LYP/cc-pVDZ level and single-point energies were calculated at the B3LYP/aug-cc-pVDZ level for selected clusters. The electronic energies were studied with respect to the geometry of the oxygen arrangement and six different characteristics of the hydrogen-bond arrangement in the cluster. Especially the effect of the placement of the non-hydrogen bonding hydrogens on the interaction energy was studied. Models for the interaction energy with respect to different characteristics of the hydrogen-bond arrangement were derived through least-square fits. The results from the study of the clusters with eight, ten and twelve molecules are used to predict possible low-energy structures for various shapes of clusters with up to 22 molecules.

  • 7.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    A theoretical study of water equilibria: The cluster distribution versus temperature and pressure for (H2O)n, n=1–60, and ice2009Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 13, s. 134302-134302-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The size distribution of water clusters at equilibrium is studied using quantum-chemical calculations in combination with statistical thermodynamics. The necessary energetic data is obtained by quantum-chemical B3LYP computations and through extrapolations from the B3LYP results for the larger clusters. Clusters with up to 60 molecules are included in the equilibrium computations. Populations of different cluster sizes are calculated using both an ideal gas model with noninteracting clusters and a model where a correction for the interaction energy is included analogous to the van der Waals law. In standard vapor the majority of the water molecules are monomers. For the ideal gas model at 1 atm large clusters [56-mer (0–120 K) and 28-mer (100–260 K)] dominate at low temperatures and separate to smaller clusters [21–22-mer (170–280 K) and 4–6-mer (270–320 K) and to monomers (300–350 K)] when the temperature is increased. At lower pressure the transition from clusters to monomers lies at lower temperatures and fewer cluster sizes are formed. The computed size distribution exhibits enhanced peaks for the clusters consisting of 21 and 28 water molecules; these sizes are for protonated water clusters often referred to as magic numbers. If cluster-cluster interactions are included in the model the transition from clusters to monomers is sharper (i.e., occurs over a smaller temperature interval) than when the ideal-gas model is used. Clusters with 20–22 molecules dominate in the liquid region. When a large icelike cluster is included it will dominate for temperatures up to 325 K for the noninteracting clusters model. Thermodynamic properties (Cp, H) were calculated with in general good agreement with experimental values for the solid and gas phase. A formula for the number of H-bond topologies in a given cluster structure is derived. For the 20-mer it is shown that the number of topologies contributes to making the population of dodecahedron-shaped cluster larger than that of a lower-energy fused prism cluster at high temperatures.

  • 8.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Computational studies of the stability of the (H2O)100 nanodrop2010Ingår i: Journal of Molecular Structure: THEOCHEM, ISSN 0166-1280, Vol. 944, nr 1-3, s. 163-167Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stability of the (H2O)100 nanodrop, experimentally known from a polyoxomolybdatecrystal structure (Müller et al. Inorg. Chem. Commun., 2003, 6, 52) and other structuresinferred from clathrate structures, are studied by quantum-chemical B3LYP computations.The free energies are compared to the trends for smaller clusters with 15-30 molecules. Forthe small clusters both cage-based structures and denser structures with a larger number of Hbondsobtained by an evolutionary algorithm (Bandow and Hartke, J. Phys. Chem. A, 2006,110, 5809) are used. The dense structures are most often found to be lower in electronicenergy. The cage-based structures, to which the structure of the experimentally found(H2O)100 cluster can be categorized, become more stable when Gibbs free energy is calculatedat 298 K. Additional cage-based clusters in the 35-81 molecular range were constructed forcomparison. The experimental cluster with 100 molecules (C2h/Ci-symmetry for oxygens/allatoms) and the constructed cluster with 42 molecules are found to be lower in energy than aplausible overall trend. The (H2O)42 cluster has an extraordinary high symmetry (S6), evenwhen the hydrogens are considered. The (H2O)100 cluster is the only of the studied clusters forwhich ΔG is negative at 298 K.

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  • 9.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    On the stability of dense versus cage-shaped water clusters: quantum-chemical investigations of zero-point energies, free energies, basis-set effects and IR spectra of (H2O)12 and (H2O)202006Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 418, s. 361-367Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The energetics of water clusters with 12 and 20 molecules are studied by quantum-chemical computations using the B3LYP, MP2, MP4 and CCSD methods. The effect of electron-correlation method, basis set, zero-point energy, thermal energy and Gibbs free energy on the relative stability of fused clusters (structures consisting of cubic- or prismatic-shaped subparts) versus cage-shaped clusters (more open structures with only three-coordinated molecules) are investigated. The O–H stretching IR vibrational spectra are studied. The contribution of zero-point and Gibbs free energy will diminish the energy difference between fused- and cage-shaped clusters, but the fused structures are still slightly more favorable.

  • 10.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Structures of the I-, II- and H-Methane Clathrates and the Ice−Methane Clathrate Phase Transition from Quantum-Chemical Modeling with Force-Field Thermal Corrections2011Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, nr 23, s. 6169-6176Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Methane hydrates with the three clathrate structures I, II and H are studied by quantumchemicalmethods. The periodic B3LYP computations are combined with force-field methodsfor the thermal energy corrections. The pressure dependencies for the crystal structures, latticeenergies and guest molecule interactions are derived. Quantum-chemical geometryoptimizations predict too small cell volumes compared to experimental data, but includingzero-point energy and thermal energy the cell volume increases and the correct densities areobtained. Phase diagram for the three structures are investigated, and phase transitions werefound at 5 GPa for the MH-I–MH-II transition and at 10 GPa for the MH-II–MH-H transition.

  • 11.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Theoretical IR spectra for water clusters (H2O)n (n = 6-22, 28, 30) and identification of spectral contributions from different H-Bond conformations in gaseous and liquid water2006Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 110, nr 50, s. 13388-13393Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vibrational IR spectra in the O-H stretching region are computed for water clusters containing 6-22, 28, and 30 molecules using quantum-chemical calculations (B3LYP and an augmented basis set). For the cluster with 20 molecules, several different structures were studied. The vibrational spectrum was partitioned into contributions from different molecules according to their coordination properties. The frequency shifts depend on the number of donated/accepted H-bonds primarily of the two molecules participating in the H-bond, but also of the surrounding molecules H-bonding to these molecules. The frequencies of H-bonds between two molecules of the same coordination type are spread over a broad interval. The most downshifted hydrogen-bond vibrations are those donated by a single-donor 3-coordinated molecule where the H-bond is accepted by a single-acceptor molecule. The H-bonded neighbors influence the downshift, and their contribution can be rationalized in the same way as for the central dimer. Single donors/acceptors cause larger downshifts than 4-coordinated molecules, and the least downshift is obtained for double donors/acceptors. This result is at variance with the conception that experimental liquid water spectra may be divided into components for which larger downshifts imply higher H-bond coordination. A mean spectral contribution for each coordination type for the donor molecule was derived and fitted to the experimental liquid water IR spectrum, which enabled an estimation of the distribution of H-bond types and average number of H-bonds (3.0 ± 0.2) in the liquid. © 2006 American Chemical Society.

  • 12.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Pohl, Anna
    Swedish Defence Research Agency.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Persson, Petter
    Lund University.
    Computational study of the catalytic effect of platinum on the decomposition of DNT2012Ingår i: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 112, nr 7, s. 1852-1858Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The catalytic decomposition of dinitrotoluene (DNT; 3-4-DNT), a by-product of the explosive trinitrotoluene (trotyl), on a platinum surface is investigated computationally. Reaction paths have been computed for a DNT molecule interacting with a Pt-cluster under varying temperatures using quantum-chemical density functional theory. Two possible initiation steps where DNT split either into nitro-tolyl and NO2, or in nitro-tolyl-oxidanyl and NO, are considered. The energy barrier for the catalytic process is found to decrease significantly for the Pt catalyzed reaction compared with the uncatalyzed reaction.

  • 13.
    Lenz, Annika
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Selegård, Linnea
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Molekylär ytfysik och nanovetenskap. Linköpings universitet, Tekniska fakulteten.
    Söderlind, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Oorganisk Kemi. Linköpings universitet, Tekniska fakulteten.
    Larsson, Arvid
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Holtz, Per-Olof
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Uvdal, Kajsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Molekylär ytfysik och nanovetenskap. Linköpings universitet, Tekniska fakulteten.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Käll, Per-Olov
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Oorganisk Kemi. Linköpings universitet, Tekniska högskolan.
    ZnO Nanoparticles Functionalized with Organic Acids: An Experimental and Quantum-Chemical Study2009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 40, s. 17332-17341Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrochemical synthesis and physical characterization of ZnO nanoparticles functionalized with four different organic acids, three aromatic (benzoic, nicotinic, and trans-cinnamic acid) and one nonaromatic (formic acid), are reported. The functionalized nanoparticles have been characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV−vis, and photoluminescence spectroscopy. The adsorption of the organic acids at ZnO nanoparticles was further analyzed and interpreted using quantum-chemical density-functional theory computations. Successful functionalization of the nanoparticles was confirmed experimentally by the measured splitting of the carboxylic group stretching vibrations as well as by the N(1s) and C(1s) peaks from XPS. From a comparison between computed and experimental IR spectra, a bridging mode adsorption geometry was inferred. PL spectra exhibited a remarkably stronger near band edge emission for nanoparticles functionalized with formic acid as compared to the larger aromatic acids. From the quantum-chemical computations, this was interpreted to be due to the absence of aromatic adsorbate or surface states in the band gap of ZnO, caused by the formation of a complete monolayer of HCOOH. In the UV−vis spectra, strong charge-transfer transitions were observed.

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