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  • 151.
    Linares, Mathieu
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Rinkevicius, Zilvinas
    Royal Institute Technology.
    Agren, Hans
    Royal Institute Technology.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Complex Polarization Propagator Approach in the Restricted Open-Shell, Self-Consistent Field Approximation: The Near K-Edge X-ray Absorption Fine Structure Spectra of Allyl and Copper Phthalocyanine2011In: JOURNAL OF PHYSICAL CHEMISTRY B, ISSN 1520-6106, Vol. 115, no 18, p. 5096-5102Article in journal (Refereed)
    Abstract [en]

    A presentation of the complex polarization propagator in the restricted open-shell self-consistent field approximation is given. It rests on a formulation of a resonant-convergent, first-order polarization propagator approach that makes it possible to directly calculate the X-ray absorption cross section at a particular frequency without explicitly addressing the excited states. The quality of the predicted X-ray spectra relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects. The method is applied to the calculation of the near K-edge X-ray absorption fine structure spectra of allyl and copper phthalocyanine. Comparison is made between the spectra of the radicals and those of the corresponding cations and anions to assess the effect of the increase of electron charge in the frontier orbital. The method offers the possibility for unique assign-lent of symmetry-independent atoms. The overall excellent spectral agreement motivates the application of the method as a routine precise tool for analyzing X-ray absorption of large systems of technological interest.

  • 152.
    Lindell, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Unge, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    de Jong, Michael P
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 16, p. 163302-1-163302-3Article in journal (Refereed)
    Abstract [en]

    In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient conditions, where direct overlap of the organic system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons.

  • 153.
    Luo, Y
    et al.
    Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Royal Inst Technol, S-10044 Stockholm, Sweden.
    Norman, Patrick
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Macak, P
    Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Royal Inst Technol, S-10044 Stockholm, Sweden.
    Agren, H
    Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Royal Inst Technol, S-10044 Stockholm, Sweden.
    Nonlinear optical susceptibilities of fullerenes in the condensed phase2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 4, p. 3060-3066Article in journal (Refereed)
    Abstract [en]

    We present results for nonlinear optical susceptibilities of fullerenes, including C-60, C-70, and C-84, in the condensed phase from large-scale nb initio calculations using self-consistent reaction field theory and an analytical local-field method. It is shown that the intermolecular polarization interaction has significant effects on the nonlinear properties of the fullerenes, and that, in some contrast to other organic species, nondipolar contributions to this interaction are important. Based on the theoretical and experimental results for the polarizability of C-60 in the gas phase, a general local-field factor for C-60 film has been obtained, which is found to be quite different from the classical Lorenz-Lorentz local-field factor. The calculated and experimental nonlinear optical susceptibilities of C-60 are in good agreement provided the comparison is made on the same basis, viz at nonresonant frequencies and considering the relevant macroscopic quantities. The dielectric and density dependence of the nonlinear optical susceptibilities of C-70 are discussed.

  • 154.
    Luo, Y
    et al.
    Royal Inst Technol, Div Theoret Chem, S-10044 Stockholm, Sweden Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Norman, Patrick
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Macak, P
    Royal Inst Technol, Div Theoret Chem, S-10044 Stockholm, Sweden Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Agren, H
    Royal Inst Technol, Div Theoret Chem, S-10044 Stockholm, Sweden Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Solvent-induced two-photon absorption of a push-pull molecule2000In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 104, no 20, p. 4718-4722Article in journal (Refereed)
    Abstract [en]

    Solvent-induced two-photon absorption cross sections are calculated for a push-pull molecule in solutions using both self-consistent reaction field and internal finite field approaches. It is shown analytically and numerically that the results from the two methods can be connected through induced local reaction field factors. The two-photon cross sections of the studied push-pull polyene are found to be rather insensitive to the choice of cavity shape. The solvent dependence of the two-photon absorption displays a pattern different from that of the first hyperpolarizability.

  • 155.
    Lövgren, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Four-component DFT calculations of phosphorescence parameters2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Oscillator strengths and transition energies are calculated for several mono-substitutes of benzene and naphthalene molecules. The substituents investigated are chlorine, bromine and iodine. Calculations for these molecules are presented, at the Hartree-Fock and DFT level of theory. The functional used in DFT is CAM-B3LYP.

  • 156.
    Macak, P.
    et al.
    Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Luo, Y.
    Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Norman, Patrick
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Agren, H.
    Ågren, H., Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Electronic and vibronic contributions to two-photon absorption of molecules with multi-branched structures2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, no 17, p. 7055-7061Article in journal (Refereed)
    Abstract [en]

    The two-photon absorption (TPA) cross-sections of series molecules with multi-branched structures was analyzed using ab initio response theory. The electronic coupling between the different arms of multi-branched molecules was found not very efficient for increasing the TPA cross-sections. In the case of two-dimensional charge-transfer cumulene-containing aromatic molecules, the TPA cross-section was drastically enhanced by increasing the dimensionality of the charge-transfer network. The vibronic coupling, was strong in multi-branched structures, which can result in an enhancement of the TPA cross-section.

  • 157.
    Macak, P
    et al.
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Royal Inst Technol, S-10044 Stockholm, Sweden.
    Norman, Patrick
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Luo, Y
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Royal Inst Technol, S-10044 Stockholm, Sweden.
    Agren, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden Royal Inst Technol, S-10044 Stockholm, Sweden.
    Modeling of dynamic molecular solvent properties using local and cavity field approaches2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 112, no 4, p. 1868-1875Article in journal (Refereed)
    Abstract [en]

    Current models of solvent properties using cavity reaction field methods are analyzed and categorized in two groups according to the use of local fields or cavity fields as the perturbing fields. Analytical connections between the two approaches are derived. (C) 2000 American Institute of Physics. [S0021-9606(00)50603-5].

  • 158.
    Magnuson, Martin
    et al.
    Uppsala University.
    Yang, L.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Guo, J.-H.
    Uppsala University.
    Såthe, C.
    Uppsala University.
    Agui, A.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Luo, Y.
    University of Stockholm.
    Ågren, H.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Johansson, N.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hornsburgh, L. E.
    University of Durham.
    Monkman, A. P.
    University of Durham.
    Resonant inelastic soft X-ray scattering spectra at the nitrogen and carbon K-edges of poly(pyridine-2,5-diyl)1999In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 101-103, p. 573-578Article in journal (Refereed)
    Abstract [en]

    Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.

  • 159.
    Magnuson, Martin
    et al.
    Uppsala University.
    Yang, L.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Guo, J.-H.
    Uppsala University.
    Såthe, C.
    Uppsala University.
    Agui, A.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Luo, Y.
    University of Stockholm.
    Ågren, H.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Johansson, N.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Hornsburgh, L. E.
    University of Durham.
    Monkman, A. P.
    University of Durham.
    The electronic structure of poly(pyridine-2,5-diyl) investigated by soft X-ray absorption and emission spectroscopies1998In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 237, no 3, p. 295-304Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and non-resonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the electron bands in line with symmetry selection and momentum conservation rules. The effect is most visual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of symmetry and are less frequency dependent.

  • 160.
    Marion, Ronan
    et al.
    University of Caen Basse Normandie, France.
    Sguerra, Fabien
    CEA, France.
    Di Meo, Florent
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Sauvageot, Elodie
    University of Caen Basse Normandie, France.
    Lohier, Jean-Francois
    University of Caen Basse Normandie, France.
    Daniellou, Richard
    University of Orleans, France.
    Renaud, Jean-Luc
    University of Caen Basse Normandie, France.
    Linares, Mathieu
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hamel, Matthieu
    CEA, France.
    Gaillard, Sylvain
    University of Caen Basse Normandie, France.
    NHC Copper(I) Complexes Bearing Dipyridylamine Ligands: Synthesis, Structural, and Photoluminescent Studies2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 17, p. 9181-9191Article in journal (Refereed)
    Abstract [en]

    We describe the synthesis of new cationic tricoordinated copper complexes bearing bidentate pyridine-type ligands and N-heterocyclic carbene as ancillary ligands. These cationic copper complexes were fully characterized by NMR, electrochemistry, X-ray analysis, and photophysical studies in different environments. Density functional theory calculations were also undertaken to rationalize the assignment of the electronic structure and the photophysical properties. These tricoordinated cationic copper complexes possess a stabilizing CH-pi interaction leading to high stability in both solid and liquid states. In addition, these copper complexes, bearing dipyridylamine ligands having a central nitrogen atom as potential anchoring point, exhibit very interesting luminescent properties that render them potential candidates for organic light-emitting diode applications.

  • 161.
    Matena, Manfred
    et al.
    Department of Physics, University of Basel, Basel, Switzerland, Donostia International Physics Center, San Sebastian, Spain .
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. Surface Science Research Centre, Department of Chemistry, University of Liverpool, Liverpool, United Kingdom.
    Wahl, Markus
    Department of Physics, University of Basel, Basel, Switzerland.
    Lee, Tien-Lin
    European Synchrotron Radiation Facility, Grenoble, France.
    Zegenhagen, Jörg
    European Synchrotron Radiation Facility, Grenoble, France.
    Gade, Lutz H.
    Anorganisch-Chemisches Institut, Universität Heidelberg, Heidelberg, Germany.
    Jung, Thomas A.
    Department of Physics, University of Basel, Basel, Switzerland, Laboratory for Micro- and Nanotechnology, Villigen, Switzerland.
    Persson, Mats
    Surface Science Research Centre, University of Liverpool, UK, Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Stöhr, Meike
    Department of Physics, University of Basel, Basel, Switzerland, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    On-surface synthesis of a two-dimensional porous coordination network: Unraveling adsorbate interactions2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, p. 125408-125415Article in journal (Refereed)
    Abstract [en]

    We present a detailed experimental and theoretical characterization of the adsorption of the perylene derivative 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) on Cu(111) and compare it to its threefold dehydrogenated derivative 3deh-DPDI, which forms in a surface reaction upon annealing. While DPDI itself does not give rise to long-range ordered structures due to lack of appropriate functional groups, 3deh-DPDI acts as an exoligand in a Cu-coordinated honeycomb network on Cu(111). The main focus of this work lies on the analysis of intermolecular and molecule-substrate interactions by combining results from scanning tunneling microscopy, x-ray photoelectron spectroscopy, x-ray standing wave measurements, and density functional theory. We show, in particular, that the interactions between metal atoms and organic ligands effectively weaken the molecule-surface interactions for 3deh-DPDI leading to an increase in molecule-substrate distances compared to the DPDI precursor. Our experimental findings also shed light on the applicability of current theories, namely van der Waals corrections to density functional theory.

  • 162.
    Medeiros, Paulo V. C.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Benzene, coronene, and circumcoronene adsorbed on gold, and a gold cluster adsorbed on graphene: Structural and electronic properties2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 20, p. 205423-Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations were performed in order to investigate the stability and the electronic structure of graphene-gold interfaces. Two configurations were studied: a gold cluster interacting with graphene and different polycyclic aromatic hydrocarbon (PAH) molecules, namely, C6H6 (benzene), C24H12 (coronene), and C54H18 (circumcoronene) adsorbed on an Au(111) surface. Nonlocal interactions were accounted for by using the semiempirical DFT-D2 method of Grimme. A limited set of calculations were also performed by using the first-principles van der Waals density functional method (vdW-DF). Adsorption distances around 3 angstrom and electronic charge transfer values of about (3-13) x 10(-3)e(-) per carbon atom were predicted for all systems. No major changes resulting from the adsorption of the gold cluster were detected in the graphenes density of states. The DFT-D2 results involving the adsorption of the PAH molecules on gold show an estimated binding energy of 73 meV per carbon atom, as well as an electronic charge loss of 0.10 x 10(-2) e(-), also per carbon atom, for an extended graphene sheet adsorbed on a gold surface. The modeling of the adsorption of C6H6 molecule on a gold surface suggests that the vdW-DF method provides more accurate results for the binding energies of such systems, in comparison to pure DFT calculations, which do not take the nonlocal interactions into account, as well as to simulations employing the DFT-D2 method.

  • 163.
    Medeiros, Paulo V. C.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 4, p. 041407-1-041407-4Article in journal (Refereed)
    Abstract [en]

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

  • 164.
    Milne, Bruce F.
    et al.
    University of Coimbra, Portugal .
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Nogueira, Fernando
    University of Coimbra, Portugal .
    Cardoso, Claudia
    University of Coimbra, Portugal .
    Marine natural products from the deep Pacific as potential non-linear optical chromophores2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 35, p. 14814-14822Article in journal (Refereed)
    Abstract [en]

    Theoretical analysis using quadratic response theory within the time-dependent density functional theory (TDDFT) formalism shows that the dermacozines, a group of phenazine-based compounds isolated from cultures of Dermacoccus abyssi found in the Mariana Trench, possess large first hyperpolarisability (beta) values at common incident laser wavelengths that are highly sensitive to the degree and type of substitution of the core structure. The phenazine moiety is a versatile and tunable chromophore for non-linear optics and this work serves to highlight the potential that (marine) natural products, even those found in the darkest places on the planet, may have for aiding developments in optical materials design.

  • 165.
    Mohammed, Abdelsalam
    et al.
    Royal Institute of Technology.
    Agren, Hans
    Royal Institute of Technology.
    Norman , Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Resonance enhanced Raman scattering from the complex electric-dipole polarizability: A theoretical study on N-22009In: CHEMICAL PHYSICS LETTERS, ISSN 0009-2614 , Vol. 468, no 4-6, p. 119-123Article in journal (Refereed)
    Abstract [en]

    An expression for resonant molecular Raman scattering in terms of the complex electric-dipole polarizability tensor is presented and implemented with first principles complex polarization propagator theory. The theory reveals the strong role of phase delays of the detected Raman radiation in the resonant case. Application on gaseous nitrogen predicts a Raman scattering enhancement of circa 104 in the resonance regions of the b(1)Pi(u) and b (1)Sigma(+)(u) states as compared to the nonresonant case.

  • 166.
    Mohammed, Abdelsalam
    et al.
    Royal Institute of Technology.
    Agren, Hans
    Royal Institute of Technology.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Time-dependent density functional theory for resonant properties: resonance enhanced Raman scattering from the complex electric-dipole polarizability2009In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ISSN 1463-9076, Vol. 11, no 22, p. 4539-4548Article in journal (Refereed)
    Abstract [en]

    Based on resonant-convergent-and thereby complex-electric-dipole polarizabilities, formulae for differential cross sections in resonant Raman spectroscopy are presented. In absorptive regions of the spectrum, there are phase delays in the induced polarization that enter the expressions for the cross sections. The theory is exemplified by calculations employing the adiabatic time-dependent density functional theory approximation, with applications on the low-lying, dipole-allowed, electronic states of a sample of molecules, including hydrogen peroxide, pyridine, and trinitrotoluene. Results obtained with the Coulomb attenuated B3LYP exchange-correlation functional are found to be more accurate than those obtained with the conventional B3LYP functional-an observation that holds not only for trinitrotoluene with its transitions of charge-transfer character but also for the other cases. The qualitative features of the resonant Raman spectra for a given molecule vary strongly from one resonance wavelength to another, which is a fact that could further facilitate the use of this spectroscopy in applications of stand-off detection of gaseous samples in ultra-low concentrations.

  • 167.
    Mohammed, Abdelsalam
    et al.
    Royal Institute of Technology.
    Minaev, Boris
    Royal Institute of Technology.
    Agren, Hans
    Royal Institute of Technology.
    Lindgren, Mikael
    Norwegian University of Science & Technology.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Classification of Raman active modes of platinum(II) acetylides: A combined experimental and theoretical study2009In: CHEMICAL PHYSICS LETTERS, ISSN 0009-2614, Vol. 481, no 4-6, p. 209-213Article in journal (Refereed)
    Abstract [en]

    Non-resonance Raman scattering of platinum(II) acetylide molecules is studied both by theory and experiment. Differential cross sections are presented for bis((4-(phenyl-ethynyl)phenyl)ethynyl)bis(tri-n-butylphosphine)platinum(II) (Pt1), and for bis((4-(phenyl-ethynyl) bis(tri-n-butylphosphine) platinum(II) substituted with triazole end group (Z1). All intense bands in the observed Raman scattering are assigned to symmetric vibrations of Pt-C C, C C, and phenyl groups; a reliable interpretation includes some details of relative intensities for the stretching and in-plane bending modes. The Raman spectra verify that the Pt-acetylide dyes remain intact during the material processing, indicating that they retain functionality for applications like in optical power limiting, nonlinear optics, and light emitting diodes.

  • 168.
    Mota, F. de B.
    et al.
    University of Federal Bahia, Salvador, Brazil .
    Rivelino, R.
    University of Federal Bahia, Salvador, Brazil .
    Medeiros, Paulo Vinicius Da Costa
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Mascarenhas, A. J. S.
    University of Federal Bahia, Salvador, Brazil .
    de Castilho, C. M. C.
    University of Federal Bahia, Salvador, Brazil .
    Hybrid platforms of graphane-graphene 2D structures: prototypes for atomically precise nanoelectronics2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 43, p. 23558-23563Article in journal (Refereed)
    Abstract [en]

    First-principles calculations demonstrate that line/ribbon defects, resulting from a controlled dehydrogenation in graphane, lead to the formation of low-dimensional electron-rich tracks in a monolayer. The present simulations point out that hybrid graphane-graphene nanostructures exhibit important elements, greatly required for the fabrication of efficient electronic circuits at the atomic level.

  • 169.
    Mozafari, Elham
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    A Theoretical Study of Charge Transport in Molecular Crystals2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main objective of this thesis is to provide a deeper understanding of the charge transport phenomena occuring in molecular crystals. The focus is on the stability and the dynamics of the polaron as the charge carrier.

    To achieve this goal, a series of numerical calculations are performed using the semi-emprical "Holstien-Peierls" model. The model considers both intra- (Holstein) and inter- (Peierls) molecular interactions, in particular the electron-phonon interactions.

    First, the stability of the polaron in an ordered two dimensional molecular lattice with an excess charge is studied using Resilient backPropagation, RPROP, algorithm. The stability is defined by the "polaron formation energy". This formation energy is obtained for a wide range of parameter sets including both intra- and inter-molecular electron-phonon coupling strengths and their vibrational frequencies, transfer intergral and electric field. We found that the polaron formation energies lying in the range of 50-100 meV are more interesting for our studies.

    The second step to cover is the dynamical behaviour of the polaron. Using the stable polaron solutions acheived in the first step, an electric field is applied as an external force, pushing the charge to move. We observed that the polaron remains stable and moves with a constant velocity for only a limited range of parameter sets. Finally, the impact of disorder and temperature on the charge dynamics is considered. Adding disorder to the system will result in a more restricted parameter set space for which the polaron is dynamically stable and mobile.

    Temperature is included in the Newtonian equations of motion via a random force. We observed that the polaron remains localized and moves with a diffusive behaviour up to a certain temperature. If the temperature increases to values above this critical temperature, the localized polaron becomes delocalized.

    All this research work is coded in MATLAB software , allowing us to run the calculations, test and validate our results.

  • 170.
    Mozafari, Elham
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Polaron dynamics in a two-dimensional Holstein-Peierls system2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 18, p. 184104-Article in journal (Refereed)
    Abstract [en]

    A semiclassical model for studying charge transport in a two-dimensional molecular lattice is presented and applied to both a well ordered system and a system with disorder. The model includes both intra- and inter-molecular electron-lattice interactions and the focus of the studies is to describe the dynamics of a charge carrier in the system. In particular, we study the dynamics of the system in which the polaron solution is dynamically stable. It is found that the parameter space for which the polaron is moving through the system is quite restricted and that the polaron is immobile for large electron-phonon coupling and weak intermolecular electron interactions and dynamically unstable and disassociates into a delocalized electronic state decoupled from the lattice for small electron-phonon coupling and strong intermolecular electron interactions. Disorder further limits the parameter space in which the polaron is mobile.

  • 171.
    Mozafari, Elham
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Polaron stability in molecular crystals2012In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 376, no 22, p. 1807-1811Article in journal (Refereed)
    Abstract [en]

    A semi-empirical Peierls-Holstein model is applied to studies of the stability of polarons in two-dimensional molecular crystal systems. Calculations for a broad range of intra- and inter-molecular parameters within this model were performed in order to obtain detailed knowledge concerning the stability of the polaron solution with respect to a rigid lattice band solution. For realistic values of the parameters the polaron solution is stable with a polaron energy in the range 50-100 meV. A metastable polaron solution is also identified. The polarons that result from our model are highly localized and it is questionable if adiabatic polaron transport can occur in the system.

  • 172. Narayan, V
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Split gate nanoscale Coulomb driven stochastic resonance mechanism for separating like-charged impurities in semiconductors2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 7Article in journal (Refereed)
    Abstract [en]

    A proposed experiment is modeled using a Monte Carlo simulation. In the simulation split gates define a nonlinear flashing potential within a semiconductor layer that contains two species of like-charged impurities with different mobilities. Flashing the external potential purifies the split gate region of the more mobile species, since impurities that have escaped are effectively unable to re-enter the split gate region. The model takes into account the Coulomb repulsion between the impurities. We demonstrate that the segregation efficiency and the purification rate are sensitive to the impurity density and strength of the confining potential, since Coulomb interaction aids the purification rate and also increases the unwanted leakage of the less mobile species.

  • 173.
    Nieto-Ortega, Belen
    et al.
    University of Malaga, Spain .
    Ramirez, Francisco J
    University of Malaga, Spain .
    Amabilino, David B
    CSIC, Spain .
    Linares, Mathieu
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Beljonne, David
    University of Mons, Belgium .
    Lopez Navarrete, Juan T
    University of Malaga, Spain .
    Casado, Juan
    University of Malaga, Spain .
    Electronic and vibrational circular dichroism spectroscopies for the understanding of chiral organization in porphyrin aggregates2012In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 48, no 73, p. 9147-9149Article in journal (Refereed)
    Abstract [en]

    Dichroic optical spectroscopies and theoretical modelling have been used to describe the structure of aggregates of porphyrins in their gels in terms of: (i) the formation of helicoidal structures, (ii) the sign of the handedness, (iii) their extent and degree of structural order, and (iv) the annealing of the structural defects.

  • 174.
    Nilsson, Roland
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Statistical Feature Selection: With Applications in Life Science2007Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The sequencing of the human genome has changed life science research in many ways. Novel measurement technologies such as microarray expression analysis, genome-wide SNP typing and mass spectrometry are now producing experimental data of extremely high dimensions. While these techniques provide unprecedented opportunities for exploratory data analysis, the increase in dimensionality also introduces many difficulties. A key problem is to discover the most relevant variables, or features, among the tens of thousands of parallel measurements in a particular experiment. This is referred to as feature selection.

    For feature selection to be principled, one needs to decide exactly what it means for a feature to be ”relevant”. This thesis considers relevance from a statistical viewpoint, as a measure of statistical dependence on a given target variable. The target variable might be continuous, such as a patient’s blood glucose level, or categorical, such as ”smoker” vs. ”non-smoker”. Several forms of relevance are examined and related to each other to form a coherent theory. Each form of relevance then defines a different feature selection problem.

    The predictive features are those that allow an accurate predictive model, for example for disease diagnosis. I prove that finding redictive features is a tractable problem, in that consistent estimates can be computed in polynomial time. This is a substantial improvement upon current theory. However, I also demonstrate that selecting features to optimize prediction accuracy does not control feature error rates. This is a severe drawback in life science, where the selected features per se are important, for example as candidate drug targets. To address this problem, I propose a statistical method which to my knowledge is the first to achieve error control. Moreover, I show that in high dimensions, feature sets can be impossible to replicate in independent experiments even with controlled error rates. This finding may explain the lack of agreement among genome-wide association studies and molecular signatures of disease.

    The most predictive features may not always be the most relevant ones from a biological perspective, since the predictive power of a given feature may depend on measurement noise rather than biological properties. I therefore consider a wider definition of relevance that avoids this problem. The resulting feature selection problem is shown to be asymptotically intractable in the general case; however, I derive a set of simplifying assumptions which admit an intuitive, consistent polynomial-time algorithm. Moreover, I present a method that controls error rates also for this problem. This algorithm is evaluated on microarray data from case studies in diabetes and cancer.

    In some cases however, I find that these statistical relevance concepts are insufficient to prioritize among candidate features in a biologically reasonable manner. Therefore, effective feature selection for life science requires both a careful definition of relevance and a principled integration of existing biological knowledge.

  • 175.
    Niskanen, J
    et al.
    University of Oulu.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Aksela, H
    University of Oulu.
    Agren, H
    Royal Institute of Technology.
    Relativistic contributions to single and double core electron ionization energies of noble gases2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, no 5, p. 054310-Article in journal (Refereed)
    Abstract [en]

    We have performed relativistic calculations of single and double core 1s hole states of the noble gas atoms in order to explore the relativistic corrections and their additivity to the ionization potentials. Our study unravels the interplay of progression of relaxation, dominating in the single and double ionization potentials of the light elements, versus relativistic one-electron effects and quantum electrodynamic effects, which dominate toward the heavy end. The degree of direct relative additivity of the relativistic corrections for the single electron ionization potentials to the double electron ionization potentials is found to gradually improve toward the heavy elements. The Dirac-Coulomb Hamiltonian is found to predict a scaling ratio of similar to 4 for the relaxation induced relativistic energies between double and single ionization. Z-scaling of the computed quantities were obtained by fitting to power law. The effects of nuclear size and form were also investigated and found to be small. The results indicate that accurate predictions of double core hole ionization potentials can now be made for elements across the full periodic table.

  • 176.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    A perspective on nonresonant and resonant electronic response theory for time-dependent molecular properties2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 46, p. 20519-20535Article in journal (Refereed)
    Abstract [en]

    The development of electronic response theory in quantum chemistry has been reviewed, starting from the early 1970s and reaching the current state-of-the-art. The general theory has been applied to the calculation of a large number of spectroscopic parameters over the years, and it has been implemented for the majority of standard electronic structure methods. Two formulations of response theory, the Ehrenfest expectation value and the quasi-energy derivative formulation, have turned into leading alternatives for the derivation of computationally tractable expressions of response functions, and they are here reviewed with an attempt to, as far as possible, leave out technical details. A set of four steps are identified as common in derivations of response functions, and the two formulations are compared along this series of steps. Particular emphasis is given to the situation when the oscillation of the weak external electromagnetic field is in resonance with a transition frequency of the system. The formation of physically sound response functions in resonance regions of the spectrum is discussed in light of the causality condition and the Kramers-Kronig relations, and it is achieved in wave function theory by means of the introduction of relaxation parameters in a manner that mimics what one sees in density matrix theory. As a working example, equations are illustrated by their application to a two-state model for para-nitroaniline including the ground and the lowest charge-transfer state in the electric dipole approximation.

  • 177.
    Norman, Patrick
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Applications of response theory with relaxation2007In: Computational Methods in Science and Engineering,2007, New York: American Institute of Physics , 2007, p. 176-Conference paper (Refereed)
    Abstract [en]

    Based on the Ehrenfest theorem, an equation-of-motion that takes relaxation into account has been presented in wave function theory, and the resulting response functions are non-divergent in the off-resonant as well as the resonant regions of the spectrum. The derivation of the linear and first-order nonlinear response functions includes exact state theory as well as single determinant approximate state theory thereby including time-dependent Hartree-Fock and Kohn-Sham theories. The response functions in this theory are complex and the methodology is coined the complex polarization propagator technique. The real and imaginary parts of the response functions may correspond to different physical observables. The present work includes applications that involve electric- and magnetic-dipole molecular properties in the visible, ultra-violet, and X-ray regions of the frequency spectrum. The real and imaginary parts of the electric-dipole polarizability and the mixed electric-dipole-magnetic-dipole polarizability are determined for S-methyl oxirane in order to calculate the polarizability, linear absorption cross section, optical rotatory dispersion, and electronic circular dichroism. The linear absorption cross section is determined in the ultra-violet region and at the carbon K-edge. The polarizability with an imaginary frequency argument is determined for formaldehyde, acetaldehyde, acetone, and methyl oxirane and the related C6, dispersion interaction coefficients are determined from the Casimir-Polder integral. As a single application of the nonlinear response function, the two-photon resonant enhanced second-harmonic generation response is determined for a -two-dimensional- pi-conjugated system.

  • 178.
    Norman, Patrick
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Aa Jensen, Hans Jorgen
    University of So Denmark.
    Phosphorescence parameters for platinum (II) organometallic chromophores: A study at the non-collinear four-component Kohn-Sham level of theory2012In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 531, p. 229-235Article in journal (Refereed)
    Abstract [en]

    A theoretical characterization of the phosphorescence decay traces of a prototypical platinum (II) organic chromophore has been conducted. The phosphorescence wavelength and radiative lifetime are predicted to equal 544 nm and 160 mu s, respectively. The third triplet state is assigned as participator in the inter-system crossing and is predicted to have a phosphorescence decay rate 12 times larger than that of the lowest triplet state. This result offers an explanation for the experimentally observed double exponential decay. The self-consistent field (SCF) optimization of the electron density was accomplished only after introducing algorithmic improvements, now incorporated in the DIRAC program.

  • 179.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Agren, H.
    Ågren, H., Laboratory of Theoretical Chemistry, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
    First-principle quantum modeling of optical power limiting materials2004In: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, Vol. 1, no 4, p. 343-366Article, review/survey (Refereed)
    Abstract [en]

    We highlight the course of development of a project initiated 1998 by the authors and concerned with quantum modeling of optical power limiting materials. The methodological development has involved various quantum mechanical technologies for a description of multi-photon excitations within the framework of wave function and density function theories, with relativistic effects being addressed at rigorous as well as more approximate levels of theory. The method development has also involved models for vibronic and solvent contributions to the multi-photon excitations as well as pulse propagation based on the solution of the classical wave equations. Our review of these issues is completely nonmathematical. Results from sample applications are discussed in order to illustrate different aspects of concern for choosing materials with good optical limiting capabilities. Some focus is given to organic and organometallic push-pull compounds, including metallo-porphyrin compounds and platinum complexes. Copyright © 2004 American Scientific Publishers. All rights reserved.

  • 180.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Bishop, David M.
    University of Ottawa, Ontario.
    Jensen, Hans Jørgen Aa.
    University of Southern Denmark, Odense.
    Oddershede, Jens
    University of Southern Denmark, Odense.
    Nonlinear response theory with relaxation: The first-order hyperpolarizability2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, p. 194103-1--18Article in journal (Refereed)
  • 181.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Bishop, D.M.
    Department of Chemistry, University of Ottawa, Ottawa, Ont. K1N 6N5, Canada.
    Jensen, H.J.Aa.
    Department of Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark.
    Oddershede, J.
    Department of Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark.
    Near-resonant absorption in the time-dependent self-consistent field and multiconfigurational self-consistent field approximations2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 22, p. 10323-10334Article in journal (Refereed)
    Abstract [en]

    Computationally tractable expressions for the evaluation of the linear response function in the multiconfigurational self-consistent field approximation were derived and implemented. The finite lifetime of the electronically excited states was considered and the linear response function was shown to be convergent in the whole frequency region. This was achieved through the incorporation of phenomenological damping factors that lead to complex response function values.

  • 182.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Cronstrand, P.
    Theoretical Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
    Ericsson, J.
    Theoretical study of linear and nonlinear absorption in platinum-organic compounds2002In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 285, no 2-3, p. 207-220Article in journal (Refereed)
    Abstract [en]

    First principle quantum chemical methods have been employed in the calculations of the linear and nonlinear ground state absorption in platinum-organic compounds, some of which include charge-transfer groups. The theoretical results show several ways to tailor the linear absorption to a desired wave length region. Spin-orbit induced transitions are discussed and characterized. The nonlinear absorption cross-sections are strongly enhanced by the introduction of charge-transfer units, whereas the linear oscillator strengths remain essentially unaffected by the same ligand substitutions. The charge-transfer substitutions are also accompanied by red-shifts in the linear absorption spectra. © 2002 Elsevier Science B.V. All rights reserved.

  • 183.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Jensen, H.J.Aa.
    Department of Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark.
    Quadratic response functions in the time-dependent four-component Hartree-Fock approximation2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 13, p. 6145-6154Article in journal (Refereed)
    Abstract [en]

    The implementation of quadratic response function in the four-component Hartree-Fock approximation was discussed. It was implemented based on the Dirac-Coulomb Hamiltonian. The second-order response function enabled the calculation of non-linear, time-dependent, corrections of the molecular polarization and magnetization. The first order response function was determined to evaluate the second-order response function.

  • 184.
    Norman, Patrick
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Jiemchooroj, Auayporn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Sernelius, Bo E.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    First principle calculations of dipole-dipole dispersion coefficients for the ground and first pi π → π* excited states of some azabenzenes2004In: Journal of Computational Methods in Science and Engineering, ISSN 1472-7978, Vol. 4, no 3, p. 321-332Article in journal (Refereed)
    Abstract [en]

    The complex polarization propagator method has been applied to the calculation of dipole-dipole dispersion coefficients (also known as C_6 coefficients) of pyridine, pyrazine, and s-tetrazine. These calculations refer to the electronic ground states as well as the first excited states of π → π* character. It is argued that accurate ground state dispersion coefficients are obtained with density functional theory using the B3LYP exchange-correlation functional. The proposed values for the C_6 coefficients of pyridine, pyrazine, and s-tetrazine in their ground states are 1543 a.u., 1398 a.u., and 1014 a.u., respectively. Multi-configurational complete active space calculations are performed on these compounds in their respective π → π* excited state. The isotropic averages of the frequency-dependent polarizabilities are smaller in the excited states, but the effective frequencies - defined in the London - van der Waals dispersion relation - are on the other hand larger.

  • 185.
    Norman, Patrick
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Jiemchooroj, Auayporn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Sernelius, Bo E.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Polarization propagator calculations of the polarizability tensor at imaginary frequencies and long-range interactions for the noble gases and n-alkanes2003In: Journal of Chemical Physics, ISSN 0021-9606, Vol. 118, no 20, p. 9167-9174Article in journal (Refereed)
    Abstract [en]

    The linear polarization propagator has been computed at imaginary frequencies for He, Ne, Ar, and Kr as well as for the n-alkanes including heptane and its smaller members. It is shown that an effective and direct evaluation of the polarization propagator using standard electronic structure first principle methods can be achieved on the whole imaginary axis without expanding the polarizability in a series of the Cauchy moments. The linear response equation will be complex in this case, but an effective algorithm can be constructed so that the computational cost parallels that of the real propagator. Calculations of the polarizability tensor are used to determine the Casimir–Polder interaction potentials for the molecules under consideration. Theoretical results for the C6 dispersion coefficient are compared with accurate experimental data, and it is shown that results for the extended n-alkanes obtained with density functional theory and the hybrid B3LYP exchange correlation functional are in excellent agreement with experiment. At the same level of theory, on the other hand, there are significant discrepancies for the noble gas atoms. The electron correlation contribution to C6 is less than 9% for the n-alkanes and decreases with the size of the system.

  • 186.
    Norman, Patrick
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Linares, Mathieu
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    On the Interplay Between Chirality and Exciton Coupling: A DFT Calculation of the Circular Dichroism in pi-Stacked Ethylene2014In: Chirality, ISSN 0899-0042, E-ISSN 1520-636X, Vol. 26, no 9, p. 483-489Article in journal (Refereed)
    Abstract [en]

    The chirality of stacked weakly interacting p-systems was interpreted in terms of Frenkel exciton states and the formation of excitonic circular dichroism (CD) bands was monitored for ethylene stacks of varying sizes. Convergence of CD bands with respect to the system size was observed for stacks involving around 10 molecules. By means of rotation around the C-C double bond in ethylene, chirality was induced in the monomeric system and which was shown to dominate the spectral responses, even for polymer aggregates. In helical assemblies of chiral entities, there will always be a mix of excitonic and monomeric contributions to the CD signal and it is demonstrated that the complex polarization propagator approach in combination with Density Functional Theory is a suitable method to address this situation.

  • 187.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics.
    Ruud, K.
    Department of Chemistry University of Tromsø.
    Microscopic theory of nonlinear optics2006In: Nonlinear optical properties of matter: From molecules to condensed phases / [ed] Manthos G. Papadopoulos, Andrzej J. Sadlej, Jerzy Leszczynski., Dordrecht: Springer , 2006, p. -694Chapter in book (Other academic)
    Abstract [en]

           

    Non-Linear Optical Properties of Matter: From Molecules to Condensed Phases attempts to draw together both theory and application in this field. As such it will be of interest to both experimentalists and theoreticians alike. Divided into two parts, Part 1 is concerned with the theory and computing of non-linear optical (NLO) properties while Part 2 reviews the latest developments in experimentation.

    Part 1: Surveys the current advances in the computation of the NLO properties of molecules, crystalline solids and nano-particles. It examines the methods employed to compute the properties of both microscopic and macroscopic forms of matter.

    Part 2: Covers the recent advances on the NLO properties of organometallic compounds, rotaxanes, glasses, Langmuir-Blodget films, gold and silver nano-particles etc. Strategies to develop novel NLO materials are also discussed along with the Hyper-Rayleigh scattering technique.

    This book will be invaluable to researchers and students in academia and industry. It will be of particular interest to anyone involved in materials science, theoretical and computational chemistry, chemical physics, and molecular physics.

  • 188.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Ruud, K.
    Department of Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
    Helgaker, T.
    Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway.
    Density-functional theory calculations of optical rotatory dispersion in the nonresonant and resonant frequency regions2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 11, p. 5027-5035Article in journal (Refereed)
    Abstract [en]

    The complex linear response function is extended to mixed electric-dipole-magnetic-dipole properties using London atomic orbitals which ensures gauge-origin independent properties. The optical rotation is determined by mixed electric-dipole-magnetic-dipole polarizability. The anomalous optical rotatory dispersion (ORD) spectra of chiral molecules is calculated using first-principle quantum-chemical methods when absorption is considered. This methodology of ORD is applied to hydrogen peroxide, 3R-methylcyclohexanone, 4R-1,1-dimethyl-[3]-(1,2)-ferrocenophan-2-on, and D2 isomer of C 84 fullerene.

  • 189.
    Norman, Patrick
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Schimmelpfennig, B.
    Theoretical Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
    Ruud, K.
    Department of Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
    Jensen, H.J.Aa.
    Department of Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark.
    Agren, H.
    Ågren, H., Theoretical Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
    Relativistic effects on linear and nonlinear polarizabilities studied by effective-core potential, Douglas-Kroll, and Dirac-Hartree-Fock response theory2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 116, no 16, p. 6914-6923Article in journal (Refereed)
    Abstract [en]

    A systematic investigation of a hierarchy of methods for including relativistic effects in the calculation of linear and nonlinear optical properties was carried out. The simple ECP method and the more involved spin-averaged Douglas-Kroll approximation were compared to benchmark results obtained with the time-dependent Dirac-Hartree-Fock method. It was found that in many cases, the performance of the ECP method exceeds its rank.

  • 190.
    Oliveira, Micael J. T.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. University of Coimbra, Portugal.
    Medeiros, Paulo V. C.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Sousa, Jose R. F.
    University of Coimbra, Portugal .
    Nogueira, Fernando
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. University of Coimbra, Portugal.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Optical and Magnetic Excitations of Metal-Encapsulating Si Cages: A Systematic Study by Time-Dependent Density Functional Theory2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 21, p. 11377-11384Article in journal (Refereed)
    Abstract [en]

    A systematic study of the optical and magnetic excitations of 12 MSi12 and four MSi10 transition metal encapsulating Si cages has been carried out by employing real time time-dependent density functional theory. Criteria for the choice of transition metals (M) are clusters stability, synthesizability, and diversity. It was found that both the optical absorption and the spin-susceptibility spectra are mainly determined by, in decreasing order of importance, (1) the cage shape, (2) the group in the Periodic Table to which M belongs, and (3) the period of M in the Periodic Table. Cages with similar structures and metal species that are close to each other in the Periodic Table possess spectra sharing many similarities; for example, the optical absorption spectra of the MSi12 (M = V, Nb, Ta, Cr, Mo, and W), which are highly symmetric and belong to groups 4 and 5 of the Periodic Table, all share a very distinctive peak at around 4 eV. In all cases, although some of the observed transitions are located at the Si skeleton of the cages, the transition metal species is always significant for the optical absorption and the spin-susceptibility spectra. Our results provide fingerprint data for identification of gas-phase MSi12 and MSi10 by optical absorption spectroscopy.

  • 191.
    Palma, Carlos-Andres
    et al.
    Technishe Universität München, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Rao, Francesco
    Albert-Ludwigs-Universität, Freiburg, Germany.
    Kühne, Dirk
    Technishe Universität München, Germany.
    Klappenberger, Florian
    Technishe Universität München, Germany.
    Barth, Johannes V.
    Technishe Universität München, Germany.
    Topological Dynamics in Supramolecular Rotors2014In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, no 8, p. 4461-4468Article in journal (Refereed)
    Abstract [en]

    Artificial molecular switches, rotors, and machines are set to establish design rules and applications beyond their biological counterparts. Herein we exemplify the role of noncovalent interactions and transient rearrangements in the complex behavior of supramolecular rotors caged in a 2D metal–organic coordination network. Combined scanning tunneling microscopy experiments and molecular dynamics modeling of a supramolecular rotor with respective rotation rates matching with 0.2 kcal mol–1 (9 meV) precision, identify key steps in collective rotation events and reconfigurations. We notably reveal that stereoisomerization of the chiral trimeric units entails topological isomerization whereas rotation occurs in a topology conserving, two-step asynchronous process. In supramolecular constructs, distinct displacements of subunits occur inducing a markedly lower rotation barrier as compared to synchronous mechanisms of rigid rotors. Moreover, the chemical environment can be instructed to control the system dynamics. Our observations allow for a definition of mechanical cooperativity based on a significant reduction of free energy barriers in supramolecules compared to rigid molecules.

  • 192.
    Palma, Carlos-Andres
    et al.
    Technishe Universität München, Garching, Germany.
    Diller, Katharina
    Technishe Universität München, Garching, Germany.
    Berger, Reinhard
    Max-Planck-Institut für Polymerforschung, Mainz, Germany.
    Welle, Alexander
    Karlsruher Institut für Technologie, Eggenstein-Leopoldshafen, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Cabellos, Jose Luis Cabellos
    Universidad del País Vasco UPV/EHU, San Sebastián, Spain.
    Mowbray, Duncan John
    Universidad del País Vasco UPV/EHU, San Sebastián, Spain.
    Papageorgiou, Anthoula C.
    Technishe Universität München, Garching, Germany.
    Ivleva, Natalia P.
    Technische Universität München, München, Germany.
    Matich, Sonja
    Walter Schottky Institut, Garching, Germany.
    Margapoti, Emanuela
    Walter Schottky Institut, Garching, Germany.
    Niesser, Reinhard
    Technische Universität München, Germany.
    Menges, Bernhard
    Max-Planck-Institut für Polymerforschung, Mainz, Germany.
    Reichert, Joachim
    Technishe Universität München, Garching, Germany.
    Feng, Xinliang
    Max-Planck-Institut für Polymerforschung, Mainz, Germany.
    Räder, Hans Joachim
    Max-Planck-Institut für Polymerforschung, Mainz, Germany.
    Klappenberger, Florian
    Technishe Universität München, Garching, Germany.
    Rubio, Angel
    Universidad del País Vasco UPV/EHU, San Sebastián, Spain.
    Müllen, Klaus
    Max-Planck-Institut für Polymerforschung, Mainz, Germany.
    Barth, Johannes V.
    Technishe Universität München, Garching, Germany.
    Photo-induced C-C reactions on insulators towards photolithography of graphene nanoarchitectures2014In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, p. 4651-4658Article in journal (Refereed)
    Abstract [en]

    On-surface chemistry for atomically precise sp2 macromolecules requires top-down lithographic methods on insulating surfaces in order to pattern the long-range complex architectures needed by the semiconductor industry. Here, we fabricate sp2-carbon nm-thin films on insulators and under ultra-high vacuum (UHV) conditions from photo-coupled brominated precursors. We reveal that covalent coupling is initiated by C-Br bond cleavage through photon energies exceeding 4.4 eV, as monitored by laser desorption ionization (LDI) mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) gives insight into the mechanisms of C-Br scission and C-C coupling processes. Further, unreacted material can be sublimed and the coupled sp2-carbon precursors can be graphitized by e-beam treatment at 500°C, demonstrating promising applications in photolithography of graphene nanoarchitectures. Our results present UV-induced reactions on insulators for the formation of all sp2-carbon architectures, thereby converging top-down lithography and bottom-up on-surface chemistry into technology.

  • 193. Paulsson, M.
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Conductance calculations through stacks of polyaromatic hydrocarbons2001In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 121, no 1-3, p. 1273-1274Article in journal (Refereed)
    Abstract [en]

    Polyaromatic hydrocarbons (PAH) can be synthesized many different sizes. They form self-assembled stacks of molecules which could be utilized in nanoelectronics applications. In this work we study stacks of PAH contacted to multichannel metallic leads. The conductance is calculated using the Landauer formula for the neutral and alkali doped stacks of PAH. We show that in the non-resonance tunneling limit the conductance is linearly related to the size of the individual PAH. A simple expression is shown to approximately describe the dependence of the conductance on the number of molecules in a stack as well as the inter-molecular interaction.

  • 194. Paulsson, M.
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Theoretical study of electron transport along self-assembled graphitic nanowires2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, no 45, p. 9433-9440Article in journal (Refereed)
    Abstract [en]

    Electron transport through stacks of polyaromatic hydrocarbons is studied theoretically using the Landauer formalism. The polyaromatic hydrocarbons can be synthesized in many different sizes and can form molecular stacks with a varying number of molecules and with a rather strong p-overlap along the stack. This allows for a large flexibility in the nanostructure of these materials and makes it possible to study the variation in the conductance with a number of different factors: a near-linear increase in the conductance as a function of the number of atoms in the individual molecule is observed. Furthermore, the conductance drops exponentially with the number of molecules in the stacks, from which it follows that an increase in the intermolecular hopping results in an increase in the conductance which is proportional to the intermolecular hopping to the power of 2(N-1), where N is the number of molecules in the stack.

  • 195.
    Paulsson, Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Self-consistent-field study of conduction through conjugated molecules2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 3, p. art. no.-035416Article in journal (Refereed)
    Abstract [en]

    Current-voltage (I-V) characteristics of individual molecules connected by metallic leads are studied theoretically. Using the Pariser-Parr-Pople quantum chemical method to model the molecule enables us to include electron-electron interactions in the Hartree approximation. The self-consistent-field method is used to calculate charging together with other properties for the total system under bias. Thereafter the Landauer formula is used to calculate the current from the transmission amplitudes. The most important parameter to understand charging is the position of the chemical potentials of the leads in relation to the molecular levels. At finite bias, the main part of the potential drop is located at the molecule-lead junctions. Also, the potential of the molecule is shown to partially follow the chemical potential closest to the highest occupied molecular orbital (HOMO). Therefore, the resonant tunneling steps in the I-V curves are smoothed giving a I-V resembling a ''Coulomb-gap." However, the charge of the molecule is not quantized since the molecule is small with quite strong interactions with the leads. The calculations predict an increase in the current at the bias corresponding to the energy gap of the molecule irrespective of the metals used in the leads. When the bias is increased further, charge is redistributed from the HOMO level to the lowest unoccupied molecular orbital of the molecule. This gives a step in the I-V curves and a corresponding change in the potential profile over the molecule. Calculations were mainly performed on polyene molecules. Molecules asymmetrically coupled to the leads model the I-V curves for molecules contacted by a scanning tunneling microscopy tip. I-V curves for pentapyrrole and another molecule that show negative differential conductance are also analyzed. The charging of these two systems depends on the shape of the molecular wave functions.

  • 196.
    Pedersen, Morten
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hedegard, Erik D.
    University of Southern Denmark, Denmark .
    Olsen, Jogvan Magnus H.
    University of Southern Denmark, Denmark .
    Kauczor, Joanna
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Kongsted, Jacob
    University of Southern Denmark, Denmark .
    Damped Response Theory in Combination with Polarizable Environments: The Polarizable Embedding Complex Polarization Propagator Method2014In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 10, no 3, p. 1164-1171Article in journal (Refereed)
    Abstract [en]

    We present a combination of the polarizable embedding (PE) scheme with the complex polarization propagator (CPP) method with the aim of calculating response properties including relaxation for large and complex systems. This new approach, termed PE-CPP, will benefit from the highly advanced description of the environmental electrostatic potential and polarization in the PE method as well as the treatment of near-resonant effects in the CPP approach. The PE-CPP model has been implemented in a Kohn-Sham density functional theory approach, and we present pilot calculations exemplifying the implementation for the UV/vis and carbon K-edge X-ray absorption spectra of the protein plastocyanin. Furthermore, technical details associated with a PE-CPP calculation are discussed.

  • 197. Pickholz, M.
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Theoretical investigation of the role of p-p interactions for the stability of phenylene ethynylene aggregates2001In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 270, no 2, p. 245-251Article in journal (Refereed)
    Abstract [en]

    A theoretical investigation of phenylene ethynylene macrocycles and oligomers aggregation was carried out. Two types of stacked supramolecular organization were investigated at the MP2 level: the intermolecular aggregation of macrocycles and the intramolecular conformational ordering of long oligomers. For the neutral monomer and ortho- and meta-macrocycles bound states of p-p stacked pairs were found, having binding energies of ~-0.061, -0.378 and -0.81 eV, respectively. The relative stability between ortho- and meta-phenylene ethynylene chains and helices as function of the oligomer length n, in gas phase was also studied. The results show that p-p interactions stabilize the helical structures for long oligomers. © 2001 Elsevier Science B.V. All rights reserved.

  • 198. Pickholz, M.
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Theoretical study of phenylene ethynylene macromolecules2001In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 121, no 1-3, p. 1271-1272Article in journal (Refereed)
    Abstract [en]

    Phenylene ethynylene oligomers are valuable as linear chain molecules with extended conjugation length and as precursors of well defined macrocycles. In this work, we investigated at the second order Møller-Plesset perturbation theory level the relative stability between helices and chains formed by phenylene ethynylene oligomers connected in ortho- and meta- positions of the phenyl rings.

  • 199.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    University of Brasilia, Brazil.
    Garganoc, Ricardo
    University of Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Concentration effects on intrachain polaron recombination in conjugated polymers2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 2, p. 1299-1308Article in journal (Refereed)
    Abstract [en]

    The influence of different charge carrier concentrations on the recombination dynamics between oppositely charged polarons is numerically investigated using a modified version of the Su-Schrieffer-Heeger (SSH) model that includes an external electric field and electron-electron interactions. Our findings show that the external electric field can play the role of avoiding the formation of excited states (polaron-exciton and neutral excitation) leading the system to a dimerized lattice. Interestingly, depending on a suitable balance between the polaron concentration and the electric field strength, the recombination mechanism can form stable polaron-excitons or neutral excitations. These results may provide guidance to improve the electroluminescence efficiency in Polymer Light Emitting Diodes.

  • 200.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Ferreira da Cunha, Wiliam
    University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Gargano, Ricardo
    University of Florida, FL 32611 USA; University of Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Temperature effects on intrachain recombination of bipolarons in conjugated polymers2014In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 614, p. 151-155Article in journal (Refereed)
    Abstract [en]

    The temperature influence over the intrachain recombination dynamics between oppositely charged bipolarons has been theoretically investigated using a version of the Su-Schrieffer-Heeger model. The results shown that, below of a critical temperature regime, these charge carriers can recombine into a biexciton. This excited state is a light emissive specie that can emit one photon and turn into an exciton state. This specie can thereafter decay to the ground state by other photon emission. This knowledge can enlighten the understanding needed to improve the internal quantum efficiency of electroluminescence in Polymer Light Emitting Diodes.

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