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  • 1.
    Alfredsson, Y.
    et al.
    Department of Physics, Uppsala University.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nilson, K.
    Department of Physics, Uppsala University.
    Åhlund, J.
    Department of Physics, Uppsala University.
    Kjeldgaard, L.
    MAX-lab, University of Lund.
    Nyberg, Mats
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Mårtensson, N.
    Department of Physics, Uppsala University.
    Sandell, A.
    Department of Physics, Uppsala University.
    Puglia, C.
    Department of Physics, Uppsala University.
    Siegbahn, H.
    Department of Physics, Uppsala University.
    Electronic structure of a vapor-deposited metal-free phthalocyanine thin film2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 21Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.

  • 2.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    First principles modeling of soft X-ray spectroscopy of complex systems2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The electronic structures of complex systems have been studied by theoretical calculations of soft x-ray spectroscopies like x-ray photoelectron spectroscopy, near edge x-ray absorption fine structure, and x-ray emission spectroscopies. A new approach based on time dependent density functional theory has been developed for the calculation of shake-up satellites associated with photoelectron spectra. This method has been applied to the phthalocyanine molecule, describing in detail its electronic structure, and revealing the origin of controversial experimental features. It is illustrated in this thesis that the theoretical intepretation plays a fundamental role in the full understanding of experimental spectra of large and complex molecular systems. Soft x-ray spectroscopies and valence band photoelectron spectroscopies have proved to be powerful tools for isomer identification, in the study of newly synthesized fullerene molecules, the azafullerene C48N12 and the C50Cl10 molecule, as well as for the determination of the conformational changes in the polymeric chain of poly(ethylene oxide). The dynamics of the core excitation process, revealed by the vibrational fine structure of the absorption resonances, has been studied by means of density functional and transition state theory approaches.

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  • 3.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Carniato, S.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Functional and basis set dependence of K-edge shake-up spectra of molecules2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 18, p. 184316-Article in journal (Refereed)
    Abstract [en]

    A straightforward approach for computing the K -edge shake-up spectra of molecules based on equivalent core-hole linear response theory at both Hartree-Fock and density functional theory levels is proposed. Benchmark calculations have been performed to explore its sensitivity to different types of functionals and basis sets for the carbon 1s shake-up spectra of benzene and metal-free phthalocyanine (H2 Pc). A very good agreement with previous theoretical and experimental works for the benzene molecule has been obtained for all the functionals and basis sets tested. Electron correlation is found to be essential for a good description of the H2 Pc system, whose experimental C 1s shake-up spectrum is best reproduced by the hybrid density functional.

  • 4.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Carniato, Stéphane
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Electronic and geometrical structures of the N1s-13(pi) excited states in the N2O moleculeManuscript (preprint) (Other academic)
  • 5.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Characterization of the electronic structure of C50Cl10 by means of soft x-ray spectroscopies2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 24, p. 244305-1-244305-4Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the last synthesized fullerene molecule, the C50Cl10, has been characterized by theoretical simulation of x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and near-edge x-ray-absorption fine structure. All the calculations were performed at the gradient-corrected and hybrid density-functional theory levels. The combination of these techniques provides detailed information about the valence band and the unoccupied molecular orbitals, as well as about the carbon core orbitals.

  • 6.
    Brena, Barbara
    et al.
    KTH, Superseded Departments, Biotechnology.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Electronic structures of azafullerene C48N122003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 14, p. 7139-7144Article in journal (Refereed)
    Abstract [en]

    Two recently proposed low-energy azafullerene C48N12 isomers have been theoretically characterized using x-ray spectroscopies. The x-ray photoelectron spectroscopy, the near-edge absorption fine structure, the x-ray emission spectroscopy, and the ultraviolet photoelectron spectroscopy for both isomers have been predicted at the gradient-corrected density functional theory level. These spectroscopies together give a comprehensive insight of the electronic structure on the core, valence, and unoccupied orbitals. They have also provided a convincing way for identifying the isomer structures.

  • 7.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Time-dependent DFT calculations of core electron shake-up states of metal-(free)-phthalocyanines2006In: Radiation Physics and Chemistry, ISSN 0969-806X, E-ISSN 1879-0895, Vol. 75, no 11, p. 1578-1581Article in journal (Refereed)
    Abstract [en]

    We have introduced a new approach for the calculation of the shake-up structures of molecular photoelectron spectra, based on the combination of time-dependent density functional theory (TD-DFT) and equivalent core hole (or Z + 1) approximation. The method, suitable for large molecules, has been applied to compute the complex shake-up states associated with the carbon Is X-ray photoelectron spectroscopy (XPS) of metal-free and nickel phthalocyanines (H2Pc and NiPc, respectively). A similar satellite profile emerges for both molecules.

  • 8.
    Brena, Barbara
    et al.
    KTH, Superseded Departments, Biotechnology.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Nyberg, Mats
    KTH, Superseded Departments, Biotechnology.
    Puglia, C.
    et al.,
    Equivalent core-hole time-dependent density functional theory calculations of carbon 1s shake-up states of phthalocyanine2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 19, p. 195214-Article in journal (Refereed)
    Abstract [en]

    The shake-up transition energies of the carbon 1s photoelectron spectrum of metal-free phthalocyanine (H2Pc) have been calculated by means of time-dependent density functional theory, for which an equivalent core approximation is adopted. Model calculations for the C 1s shake-up states of benzene are in excellent agreement with the latest experimental results. The complex C 1s shake-up structures associated with the aromatic and pyrrole carbons in the phthalocyanine are computed, as well as their ionization potentials. They allow us to determine the origin of the anomalous intensity ratio between the pyrrole and benzene carbons in a high resolution C 1s photoelectron spectrum measured for a H2Pc film, as due to a benzene-related shake-up contribution, hidden under the pyrrole main intensity feature.

  • 9.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nordlund, D
    Odelius, M
    Ogasawara, H
    Nilsson, A
    Pettersson, L G M
    Ultrafast molecular dissociation of water in ice2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 14, p. 148302-Article in journal (Refereed)
    Abstract [en]

    Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path.

  • 10.
    Brena, Barbara
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Palmgren, Pål
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Nilson, Katharina
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Hennies, F.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Agnarsson, Björn
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Önsten, Anneli
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    InSb-TiOPc interfaces: Band alignment, ordering and structure dependent HOMO splitting2009In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, no 20, p. 3160-3169Article in journal (Refereed)
    Abstract [en]

    Thin films of titanyl phthalocyanine (TiOPc) have been adsorbed on InSb(1 1 1) (3 x 3) and InSb(1 0 0) c(8 x 2) surfaces and studied with respect to their electronic structure using photoemission (PES), density functional theory (DFT) and scanning tunneling microscopy (STM). The interface chemical interaction is weak in both cases; no adsorbate induced surface band bending is observed and the energy level alignment across the interface is determined by the original position of the substrate Fermi level and the charge neutrality level of the molecule. Room temperature adsorption results in disordered films on both surfaces. The behaviors after annealing are different; on InSb(1 0 0) well-ordered molecular chains form along and on top of the In-rows, whereas on (1 1 1) no long range order is observed. The disorder leads to intermolecular interactions between the titanyl group and neighboring benzene rings leading to a split of TiOPc HOMO (highest occupied molecular orbital) by as much as 0.8 eV.

  • 11.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Zhuang, G. V.
    Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley.
    Augustsson, A.
    Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley.
    Liu, G.
    Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley.
    Nordgren, J.
    Department of Physics, Uppsala University.
    Guo, J. H.
    Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley.
    Ross, P. N.
    Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Conformation dependence of electronic structures of poly(ethylene oxide)2005In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, no 16, p. 7907-7914Article in journal (Refereed)
    Abstract [en]

    The electronic structure of pure poly(ethylene oxide) (PEO) for four different polymeric chain conformations has been studied by Hartree-Fock (HF) and density functional theory (DFT) through the analysis of their valence band photoelectron spectroscopy (VB-PES), X-ray emission spectroscopy (XES), and resonant inelastic X-ray scattering (RIXS). It is shown that the valence band of PEO presents specific conformation dependence, which can be used as a fingerprint of the polymeric structures. The calculated spectra have been compared with experimental results for PEO powder.

  • 12. Carniato, Stéphane
    et al.
    Taïeb, Richard
    Kukk, Edwin
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    N-K near edge x-ray absorption fine structures of acetonitrile in gas phase2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 21, p. 214301-Article in journal (Refereed)
    Abstract [en]

     The dynamic processes of N(1s) core-hole excitation in gas-phase CH3CN molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N-K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of nu((CN)) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.

  • 13.
    O'Shea, J. N.
    et al.
    School of Physics and Astronomy, University of Nottingham.
    Swarbrick, J. C.
    School of Physics and Astronomy, University of Nottingham.
    Nilson, K.
    Department of Physics, Uppsala University.
    Puglia, C.
    Department of Physics, Uppsala University.
    Brena, Barbara
    KTH, Superseded Departments, Biotechnology.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Dhanak, V. R.
    Department of Physics, University of Liverpool.
    Molecular ordering in isonicotinic acid on rutile TiO2(110) investigated with valence band photoemission2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 20, p. 10203-10208Article in journal (Refereed)
    Abstract [en]

    The adsorption of isonicotinic acid on rutile TiO2(110) has been investigated using synchrotron-based valence band photoemission. Structural ordering in multilayer films of the molecules is found to give rise to a strong angular dependence in the valence band intensities when measured using linearly polarized radiation. Molecular ordering in this case is proposed to be induced by intermolecular hydrogen bonding which is found to be highly dependent upon the deposition rate of the isonicotinic acid. Through comparison of the experimental data with density functional calculated valence band spectra of hydrogen-bonded isonicotinic acid molecules, we can account for the angular dependence in terms of the spatial distribution of the molecular orbitals.

  • 14.
    Åhlund, John
    et al.
    Department of Physics, Uppsala University.
    Nilson, Katharina
    Department of Physics, Uppsala University.
    Schiessling, Joachim
    Department of Physics, Uppsala University.
    Kjeldgaard, Lisbeth
    MAX-lab., University of Lund.
    Berner, Simon
    Department for Surface Biotechnology, BMC, Uppsala.
    Mårtensson, Nils
    Department of Physics, Uppsala University.
    Puglia, Carla
    Department of Physics, Uppsala University.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nyberg, Mats
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    The electronic structure of iron phthalocyanine probed by photoelectron and x-ray absorption spectroscopies and density functional theory calculations2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 3, p. 034709-1-034709-7Article in journal (Refereed)
    Abstract [en]

    A joint experimental and theoretical work to explain the electronic and geometrical structure of an in situ prepared film of iron phthalocyanine (FePc) on silicon (100) is presented. FePc molecular films have been characterized by core and valence photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS), and the results have been interpreted and simulated by density functional theory (DFT) calculations. C1s and N1s PE spectra have been analyzed by taking into account all chemically nonequivalent C and N atoms in the molecule. In the Fe2p(3/2) spectra it has been possible to resolve two components that can be related to the open shell structure of the molecule. By valence PES and N1s XAS data, the geometrical orientation of the FePc molecules in the film could be determined. Our results indicate that for the FePc on Si(100), the molecules within the film are mainly standing on the surface. The experimental N1s XAS spectra are very well reproduced by the theoretical calculations, which are both angle and atomic resolved, giving a detailed description of the electronic and geometric structure of the FePc film. Furthermore, the asymmetry and the intensity angle variation of the first N1s XAS threshold feature could be explained by the presented DFT calculations as due to the chemical nonequivalence of the N atoms and the symmetry character of the lowest unoccupied molecular orbital.

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