Change search
Refine search result
1234 1 - 50 of 171
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1. Ahrén, M.
    et al.
    Selegård, L.
    Söderlind, F.
    Linares, M.
    Kauczor, J.
    Norman, Patrick
    Käll, P. -O
    Uvdal, K.
    A simple polyol-free synthesis route to Gd 2O 3 nanoparticles for MRI applications: An experimental and theoretical study2012In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 14, no 8, 1006Article in journal (Refereed)
    Abstract [en]

    Chelated gadolinium ions, e.g., Gd-DTPA, are today used clinically as contrast agents for magnetic resonance imaging (MRI). An attractive alternative contrast agent is composed of gadolinium oxide nanoparticles as they have shown to provide enhanced contrast and, in principle, more straightforward molecular capping possibilities. In this study, we report a new, simple, and polyol-free way of synthesizing 4-5-nm-sized Gd 2O 3 nanoparticles at room temperature, with high stability and water solubility. The nanoparticles induce high-proton relaxivity compared to Gd-DTPA showing r 1 and r 2 values almost as high as those for free Gd 3+ ions in water. The Gd 2O 3 nanoparticles are capped with acetate and carbonate groups, as shown with infrared spectroscopy, near-edge X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and combined thermogravimetric and mass spectroscopy analysis. Interpretation of infrared spectroscopy data is corroborated by extensive quantum chemical calculations. This nanomaterial is easily prepared and has promising properties to function as a core in a future contrast agent for MRI. © 2012 Springer Science+Business Media B.V.

  • 2. Aidas, Kestutis
    et al.
    Angeli, Celestino
    Bak, Keld L.
    Bakken, Vebjorn
    Bast, Radovan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Boman, Linus
    Christiansen, Ove
    Cimiraglia, Renzo
    Coriani, Sonia
    Dahle, Pal
    Dalskov, Erik K.
    Ekstrom, Ulf
    Enevoldsen, Thomas
    Eriksen, Janus J.
    Ettenhuber, Patrick
    Fernandez, Berta
    Ferrighi, Lara
    Fliegl, Heike
    Frediani, Luca
    Hald, Kasper
    Halkier, Asger
    Hattig, Christof
    Heiberg, Hanne
    Helgaker, Trygve
    Hennum, Alf Christian
    Hettema, Hinne
    Hjertenaes, Eirik
    Host, Stinne
    Hoyvik, Ida-Marie
    Iozzi, Maria Francesca
    Jansik, Branislav
    Jensen, Hans Jorgen Aa.
    Jonsson, Dan
    Jorgensen, Poul
    Kauczor, Joanna
    Kirpekar, Sheela
    Kjrgaard, Thomas
    Klopper, Wim
    Knecht, Stefan
    Kobayashi, Rika
    Koch, Henrik
    Kongsted, Jacob
    Krapp, Andreas
    Kristensen, Kasper
    Ligabue, Andrea
    Lutnaes, Ola B.
    Melo, Juan I.
    Mikkelsen, Kurt V.
    Myhre, Rolf H.
    Neiss, Christian
    Nielsen, Christian B.
    Norman, Patrick
    Olsen, Jeppe
    Olsen, Jogvan Magnus H.
    Osted, Anders
    Packer, Martin J.
    Pawlowski, Filip
    Pedersen, Thomas B.
    Provasi, Patricio F.
    Reine, Simen
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Ruden, Torgeir A.
    Ruud, Kenneth
    Rybkin, Vladimir V.
    Salek, Pawel
    Samson, Claire C. M.
    de Meras, Alfredo Sanchez
    Saue, Trond
    Sauer, Stephan P. A.
    Schimmelpfennig, Bernd
    Sneskov, Kristian
    Steindal, Arnfinn H.
    Sylvester-Hvid, Kristian O.
    Taylor, Peter R.
    Teale, Andrew M.
    Tellgren, Erik I.
    Tew, David P.
    Thorvaldsen, Andreas J.
    Thogersen, Lea
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Watson, Mark A.
    Wilson, David J. D.
    Ziolkowski, Marcin
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    The Dalton quantum chemistry program system2014In: Wiley Interdisciplinary Reviews. Computational Molecular Science, ISSN 1759-0876, Vol. 4, no 3, 269-284 p.Article in journal (Refereed)
    Abstract [en]

    Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.

  • 3. Al-Saidi, W. A.
    et al.
    Asher, S. A.
    Norman, Patrick
    Resonance raman spectra of TNT and RDX using vibronic theory, excited-state gradient, and complex polarizability approximations2012In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 116, no 30, 7862-7872 p.Article in journal (Refereed)
    Abstract [en]

    Geometries, UV absorption bands, and resonance Raman (RR) cross sections of TNT and RDX are investigated using density functional theory (DFT) in conjunction with the Coulomb attenuated B3LYP exchange-correlation functional. The absorption and RR spectra are determined with use of vibronic (VB) theory, excited-state gradient, and complex polarizability (CPP) approximations. We examined low-energy isomers (two for TNT and four for RDX) whose energies differ by less than 1 kcal/mol, such that they would appreciably be populated at room temperature. The two TNT isomers differ by an internal rotation of the methyl group, while the four conformers of RDX differ by the arrangements of the nitro group relative to the ring. Our theoretical optical properties of the TNT and RDX isomers are in excellent agreement with experimental and recent CCSD-EOM results, respectively. For the two TNT isomers, the ultraviolet RR (UVRR) spectra are similar and in good agreement with recently measured experimental results. Additionally, the UVRR spectra computed using the excited-state and CPP approaches compare favorably with the VB theory results. On the other hand, the RR spectra of the RDX conformers differ from one another, reflecting the importance of the positioning of the NO 2 groups with respect to the ring. In the gas phase or in solution, RDX would give a spectrum associated with a conformationally averaged structure. It is encouraging that the computed spectra of the conformers show similarities to recent measured RDX spectra in acetonitrile solution, and reproduce the 10-fold decrease in the absolute Raman cross sections of RDX compared to TNT for the observed 229 nm excitation. We show that in TNT and RDX vibrational bands that couple to NO 2 or the ring are particularly resonance enhanced. Finally, the computed RDX spectra of the conformers present a benchmark for understanding the RR spectra of the solid-phase polymorphs of RDX. © 2012 American Chemical Society.

  • 4. Baev, A.
    et al.
    Welinder, P.
    Erlandsson, R.
    Henriksson, J.
    Norman, P.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    A quantum mechanical - Electrodynamical approach to nonlinear properties: Application to optical power limiting with platinum-organic compounds2007In: Journal of nonlinear optical physics and materials, ISSN 0218-8635, Vol. 16, no 2, 157-169 p.Article in journal (Refereed)
    Abstract [en]

    Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach - the quantum mechanical-electrodynamical (QMED) approach - is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds. © World Scientific Publishing Company.

  • 5. Baev, A.
    et al.
    Welinder, P.
    Erlandsson, R.
    Henriksson, J.
    Norman, P.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Light-matter interaction of strong laser pulses in the micro-, nano-, and picosecond regimes2007In: Materials Research Society Symposium Proceedings, 2007, 12-29 p.Conference paper (Refereed)
    Abstract [en]

    Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical (QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell s equations. This allows to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation allows to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime it is often necessary to account simultaneously for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is here highlighted in a study of the optical power limiting with platinum-organic molecular compounds. © 2007 Materials Research Society.

  • 6. Baev, Alexander
    et al.
    Norman, Patrick
    Henriksson, Johan
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Theoretical Simulations of clamping levels in optical power limiting2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 42, 20912-20916 p.Article in journal (Refereed)
    Abstract [en]

    Multiphysics modeling, combining quantum mechanical and classical wave mechanical theories, of clamping levels has been performed for a platinum(II) organic compound in a sol-gel glass matrix. A clamping level of 2.5 mu J is found for a pulse duration of 10 ns. The excited-state absorption in the triplet manifold is shown to be crucial for clamping to occur.

  • 7. Baev, Alexander
    et al.
    Welinder, Pontus
    Erlandsson, Robert
    Henriksson, Johan
    Norman, Patrick
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    A quantum mechanical - Electrodynamical approach to nonlinear properties: Application to optical power limiting with platinum-organic compounds2007In: Journal of nonlinear optical physics and materials, ISSN 0218-8635, Vol. 16, no 2, 157-169 p.Article in journal (Refereed)
    Abstract [en]

    Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical ( QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds.

  • 8. Bast, R.
    et al.
    Saue, T.
    Henriksson, J.
    Norman, P.
    Role of noncollinear magnetization for the first-order electric-dipole hyperpolarizability at the four-component Kohn-Sham density functional theory level2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 2, 024109Article in journal (Refereed)
    Abstract [en]

    The quadratic response function has been derived and implemented at the adiabatic four-component Kohn-Sham density functional theory level with inclusion of noncollinear spin magnetization and gradient corrections in the exchange-correlation functional-a work that is an extension of our previous report where magnetization dependencies in the exchange-correlation functional were ignored [J. Henriksson, T. Saue, and P. Norman, J. Chem. Phys. 128, 024105 (2008)]. The electric-field induced second-harmonic generation experiments on CF3 Cl and CF3 Br are addressed by a determination of Β- (-2ω;ω,ω) for a wavelength of 694.3 nm, and the same property is also determined for CF3 I. The relativistic effects on the static hyperpolarizability for the series of molecules amount to 1%, 5%, and 9%, respectively. At the experimental wavelength, the contributions to Β due to the magnetization dependence in the exchange-correlation functional are negligible for CF3 Cl and CF3 Br and small for CF 3 I. The noticeable effect of magnetization in the latter case is attributed to a near two-photon resonance with the excited state 1 E3 (nonrelativistic notation). It is emphasized, however, that the effect of magnetization on Β for CF3 I is negligible both in comparison to the total relativistic correction as well as to the effects of electron correlation. It is concluded that, in calculations of hyperpolarizabilities under nonresonant conditions, the magnetization dependence in the exchange-correlation functional may be ignored. © 2009 American Institute of Physics.

  • 9. Birke, R. L.
    et al.
    Lombardi, J. R.
    Saidi, W. A.
    Norman, P.
    Surface-Enhanced Raman Scattering Due to Charge-Transfer Resonances: A Time-Dependent Density Functional Theory Study of Ag13-4-Mercaptopyridine2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 37, 20721-20735 p.Article in journal (Refereed)
    Abstract [en]

    We have used time-dependent density functional theory in conjunction with the CAM-B3LYP functional and MWB28/aug-cc-pVDZ basis set to determine non-, near-, and on-resonance Raman spectra for a complex formed by 4-mercaptopyridine (4-Mpy) binding with a Ag13 cluster via the thiolate Ag-S bond. Geometry optimizations of the Ag13-4-Mpy complex showed an on-top structure directly bound to one Ag atom with the ring of the molecule almost flat with respect to two Ag atoms of the complex. The corresponding B3LYP/MWB28/aug-cc-pVDZ geometry is also an on-top structure directly bound to one Ag atom, but the molecule is directed away from the surface. The near-resonance Raman calculations were carried out in the infinite lifetime approximation, while the on-resonant Raman excitation profiles were calculated with the complex polarization propagator (CPP) approach, introducing a half width at half-maximum spectral broadening of 0.2 eV. Calculation of the UV-vis spectra of the isolated 4-Mpy and of the Ag13-4-Mpy complex showed that binding shifts the spectra from deep in the UV to the visible region. Calculation of the near-resonance Raman spectra of the two structures of the complex at 410 (3.025 eV) and 425 nm (2.918 eV) showed a strong enhancement. A very large variation across vibrational modes by a factor of at least 103 was found for both the static chemical enhancement and charge-transfer (CT) enhancement mechanisms. This large variation in enhancement factor indicates that B-term Herzberg-Teller scattering is occurring because inactive or very low intensity modes in the static spectra of the molecule are much stronger in both the static and near-resonance spectra of the complex. From the excitation profile using the CPP method, an overall surface enhancement on the order 103 or higher was found for individual modes on excitation into a CT excited state. © 2016 American Chemical Society.

  • 10. Bishop, D. M.
    et al.
    Norman, P.
    Effects of vibration on the polarizability and the first and second hyperpolarizabilities of HF, HCl, and HBr1999In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 111, no 7, 3042-3050 p.Article in journal (Refereed)
    Abstract [en]

    We report calculations, using electron uncorrelated and correlated wave functions, of the electronic and vibrational properties which pertain to certain nonlinear optical properties for HF, HCl, and HBr. Our main focus is on vibrational effects (zero-point-vibrational averaging and pure vibration). Analysis of the results obtained at various levels of approximation indicates that first-order perturbation theory is generally adequate for finding the zero-point-vibrational-averaging corrections for these molecules and that complete second-order perturbation theory nearly always gives reliable results for the pure vibrational corrections. Attention is drawn to some differences with previously published results for these properties. © 1999 American Institute of Physics.

  • 11. Bishop, David M.
    et al.
    Norman, Patrick
    Calculations of dynamic hyperpolarizabilities for small and medium sized molecules2001In: Handbook of Advanced Electronic and Photonic Materials / [ed] H. S. Nalwa, San Diego: Academic Press, 2001Chapter in book (Refereed)
  • 12.
    Boström, Mathias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Ninham, Barry W.
    Norman, Patrick
    Sernelius, Bo E.
    Resonance interaction induced by metal surfaces catalyzes atom-pair breakage2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 4, 044701- p.Article in journal (Refereed)
    Abstract [en]

    We present the theory for retarded resonance interaction between two identical atoms at arbitrary positions near a metal surface. The dipole-dipole resonance interaction force that binds isotropically excited atom pairs together in free space may turn repulsive close to an ideal (totally reflecting) metal surface. On the other hand, close to an infinitely permeable surface it may turn more attractive. We illustrate numerically how the dipole-dipole resonance interaction between two oxygen atoms near a metal surface may provide a repulsive energy of the same order of magnitude as the ground-state binding energy of an oxygen molecule. As a complement we also present results from density-functional theory.

  • 13. Christodoulou, C.
    et al.
    Giannakopoulos, A.
    Nardi, M. V.
    Ligorio, G.
    Oehzelt, M.
    Chen, L.
    Pasquali, L.
    Timpel, M.
    Giglia, A.
    Nannarone, S.
    Norman, P.
    Linares, M.
    Parvez, K.
    Müllen, K.
    Beljonne, D.
    Koch, N.
    Tuning the work function of graphene-on-quartz with a high weight molecular acceptor2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 9, 4784-4790 p.Article in journal (Refereed)
    Abstract [en]

    Ultraviolet and X-ray photoelectron spectroscopies in combination with density functional theory (DFT) calculations were used to study the change in the work function (Φ) of graphene, supported by quartz, as induced by adsorption of hexaazatriphenylene-hexacarbonitrile (HATCN). Near edge X-ray absorption fine structure spectroscopy (NEXAFS) and DFT modeling show that a molecular-density-dependent reorientation of HATCN from a planar to a vertically inclined adsorption geometry occurs upon increasing surface coverage. This, in conjunction with the orientation-dependent magnitude of the interface dipole, allows one to explain the evolution of graphene Φ from 4.5 eV up to 5.7 eV, rendering the molecularly modified graphene-on-quartz a highly suitable hole injection electrode. © 2014 American Chemical Society.

  • 14. Coriani, S.
    et al.
    Christiansen, O.
    Fransson, T.
    Norman, P.
    Coupled-cluster response theory for near-edge x-ray-absorption fine structure of atoms and molecules2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 2, 022507Article in journal (Refereed)
    Abstract [en]

    Based on an asymmetric Lanczos-chain subspace algorithm, damped coupled cluster linear response functions have been implemented for the hierarchy of coupled cluster (CC) models including CC with single excitations (CCS), CC2, CC with single and double excitations (CCSD), and CCSD with noniterative triple corrected excitation energies CCSDR(3). This work is a first step toward the extension of these theoretical electronic structure methods of well-established high accuracy in UV-vis absorption spectroscopies to applications concerned with x-ray radiation. From the imaginary part of the linear response function, the near K-edge x-ray absorption spectra of neon, water, and carbon monoxide are determined and compared with experiment. Results at the CCSD level show relative peak intensities in good agreement with experiment with discrepancies in transition energies due to incomplete treatment of electronic relaxation and correlation that amount to 1-2 eV. With inclusion of triple excitations, errors in energetics are less than 0.9 eV and thereby capturing 90%, 95%, and 98% of the relaxation-correlation energies for C, O, and Ne, respectively. © 2012 American Physical Society.

  • 15. Coriani, S.
    et al.
    Fransson, T.
    Christiansen, O.
    Norman, P.
    Asymmetric-lanczos-chain-driven implementation of electronic resonance convergent coupled-cluster linear response theory2012In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 5, 1616-1628 p.Article in journal (Refereed)
    Abstract [en]

    We present an implementation of the damped coupled-cluster linear response function based on an asymmetric Lanczos chain algorithm for the hierarchy of coupled-cluster approximations CCS (coupled-cluster singles), CC2 (coupled-cluster singles and approximate doubles), and CCSD (coupled-cluster singles and doubles). Triple corrections to the excitation energies can be included via the CCSDR(3) (coupled-cluster singles and doubles with noniterative-triples-corrected excitation energies) approximation. The performance and some of the potentialities of the approach are investigated in calculations of the visible/ultraviolet absorption spectrum and the dispersion of the real polarizability in near-resonant regions of pyrimidine, the near-edge absorption fine structure (NEXAFS) of ammonia, and the direct determination of the C 6 dipole-dipole dispersion coefficient of the benzene dimer. © 2012 American Chemical Society.

  • 16.
    Cronstrand, Peter
    et al.
    KTH.
    Christiansen, O.
    Norman, P.
    Agren, H.
    Theoretical calculations of excited state absorption2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 23, 5357-5363 p.Article in journal (Refereed)
    Abstract [en]

    Excitation energies and transition dipole moments between excited electronic states have been calculated using various theoretical methods to investigate the ability to describe excited state absorption. Quadratic response theory is used in combination with self-consistent field, multi-configurational self-consistent field, and coupled-cluster electronic structure methods. The results of these different methods are compared. The set of molecules considered includes lithium hydride, carbon monoxide, formaldehyde, formamide, and symtetrazine. For some of the molecules results are also compared with the method of applying linear response theory to an excited state wavefunction separately optimized by means of the multi-configurational self-consistent field method.

  • 17.
    Cronstrand, Peter
    et al.
    KTH.
    Christiansen, O.
    Norman, P.
    Ågren, H.
    Ab initio modeling of excited state absorption of polyenes2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 13, 2567-2575 p.Article in journal (Refereed)
    Abstract [en]

    Vertical excitation energies and transition dipole moments between excited electronic states have been calculated for the trans-polyenes series C 4H 6-C 12H 14 in order to study the formation of excited state absorption spectra of these species. Quadratic response theory is applied in conjunction with the self-consistent field method and a hierarchical set of coupled-cluster methods. The convergence of the excited state absorption, with respect to wavefunction and treatment of electron correlation and also the length of the oligomer unit, is studied, revealing a considerable demand on the computational effort in order to predict the excited state spectra with precision. The organization of the excited states is found to change in character along the polyene series. The inflexion point for the vertical excitation energies between the one-photon allowed 1 1B u and the two-photon 2 1A g state is predicted to occur between hexatriene and octatetraene. Good agreement with experiment is obtained for butadiene and hexatriene for which the most accurate calculations have been carried out.

  • 18.
    Cronstrand, Peter
    et al.
    KTH, Superseded Departments, Biotechnology.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Norman, P.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Ab initio calculations of three-photon absorption2003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 375, no 02-jan, 233-239 p.Article in journal (Refereed)
    Abstract [en]

    We present large scale ab initio calculations of three-photon absorption of a series of dithienothiophene based charge transfer molecules using response theory within the random phase approximation. The structure-to-property relations obtained for the three-photon absorption cross-sections are discussed and compared with those for one- and two-photon absorption.

  • 19.
    Cronstrand, Peter
    et al.
    KTH, Superseded Departments, Chemistry.
    Norman, P.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Few-states models for three-photon absorption2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 5, 2020-2029 p.Article in journal (Refereed)
    Abstract [en]

    Few-states models are derived for the calculation of three-photon absorption matrix elements. Together with earlier derived few-states models for two-photon absorption, the models are evaluated against results from response theory calculations that provide the full sum-over-states values. It is demonstrated that not even for systems with charge-transfer character, where few-states models for two-photon absorption are in excellent agreement with response theory, do the models provide a quantitatively correct description for three-photon absorption. The convergence behavior, merits, and shortcomings of the models are elucidated in some detail. The role of various characteristics of the electronic structure, such as symmetry, charge transfer, and conjugation-important for the formation of a large three-photon cross section-is analyzed. As for two-photon absorption cross sections, it is essential to consider generalized few-states models also for three-photon absorption, that is, to account for dipolar directions and laser beam polarization. Despite their poor quantitative performance, it is argued that few-states models at times can be useful for interpretation purposes when applied to three-photon absorption.

  • 20. Cukras, J.
    et al.
    Coriani, S.
    Decleva, P.
    Christiansen, O.
    Norman, P.
    Photoionization cross section by Stieltjes imaging applied to coupled cluster Lanczos pseudo-spectra2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, no 9, 094103Article in journal (Refereed)
    Abstract [en]

    A recently implemented asymmetric Lanczos algorithm for computing (complex) linear response functions within the coupled cluster singles (CCS), coupled cluster singles and iterative approximate doubles (CC2), and coupled cluster singles and doubles (CCSD) is coupled to a Stieltjes imaging technique in order to describe the photoionization cross section of atoms and molecules, in the spirit of a similar procedure recently proposed by Averbukh and co-workers within the Algebraic Diagrammatic Construction approach. Pilot results are reported for the atoms He, Ne, and Ar and for the molecules H2, H2O, NH3, HF, CO, and CO2. © 2013 AIP Publishing LLC.

  • 21. Cukras, J.
    et al.
    Kauczor, J.
    Norman, P.
    Rizzo, A.
    Rikken, G. L. J. A.
    Coriani, S.
    A complex-polarization-propagator protocol for magneto-chiral axial dichroism and birefringence dispersion2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 19, 13267-13279 p.Article in journal (Refereed)
    Abstract [en]

    A computational protocol for magneto-chiral dichroism and magneto-chiral birefringence dispersion is presented within the framework of damped response theory, also known as complex polarization propagator theory, at the level of time-dependent Hartree-Fock and time-dependent density functional theory. Magneto-chiral dichroism and magneto-chiral birefringence spectra in the (resonant) frequency region below the first ionization threshold of R-methyloxirane and l-alanine are presented and compared with the corresponding results obtained for both the electronic circular dichroism and the magnetic circular dichroism. The additional information content yielded by the magneto-chiral phenomena, as well as their potential experimental detectability for the selected species, is discussed. © the Owner Societies 2016.

  • 22. Di Meo, F.
    et al.
    Pedersen, M. N.
    Rubio-Magnieto, J.
    Surin, M.
    Linares, M.
    Norman, P.
    DNA electronic circular dichroism on the inter-base pair scale: An experimental-theoretical case study of the at homo-oligonucleotide2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 3, 355-359 p.Article in journal (Refereed)
    Abstract [en]

    A successful elucidation of the near-ultraviolet electronic circular dichroism spectrum of a short double-stranded DNA is reported. Time-dependent density functional theory methods are shown to accurately predict spectra and assign bands on the microscopic base-pair scale, a finding that opens the field for using circular dichroism spectroscopy as a sensitive nanoscale probe of DNA to reveal its complex interactions with the environment. (Chemical Equation Presented). © 2015 American Chemical Society.

  • 23. Ekström, U.
    et al.
    Norman, Patrick
    Linköping University, Sweden.
    X-ray absorption spectra from the resonant-convergent first-order polarization propagator approach2006In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, no 4, 042722Article in journal (Refereed)
    Abstract [en]

    The one-photon absorption cross sections of molecular systems have been determined in the high-energy region from the imaginary part of the electric dipole polarizability tensor. In contrast to commonly adopted state-specific methodologies, the complex polarization propagator approach does not require explicit consideration of the excited states and it is open-ended towards multiphoton absorption. It is shown that the electronic relaxation in the core-hole state is well accounted for in the present approach with use of standard density-functional based electronic structure methods. Sample calculations are presented of the K -edge x-ray absorption spectra for H2 O, CO, C4 H4 N, and C6 H6.

  • 24. Ekström, U.
    et al.
    Norman, Patrick
    Linkoping University, Sweden.
    Carravetta, V.
    Relativistic four-component static-exchange approximation for core-excitation processes in molecules2006In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 73, no 2, 022501Article in journal (Refereed)
    Abstract [en]

    A generalization of the static-exchange approximation for core-electron spectroscopies to the relativistic four-component realm is presented. The initial state is a Kramers restricted Hartree-Fock state and the final state is formed as the configuration-interaction single excited state, based on the average of configurations for (n-1) electrons in n near-degenerate core orbitals for the reference ionic state. It is demonstrated that the static-exchange Hamiltonian can be made real by considering a set of time-reversal symmetric electron excitation operators. The static-exchange Hamiltonian is constructed at a cost that parallels a single Fock matrix construction in a quaternion framework that fully exploits time-reversal and spatial symmetries for the D2h point group and subgroups. The K - and L -edge absorption spectra of H2 S are used to illustrate the methodology. The calculations adopt the Dirac-Coulomb Hamiltonian, but the theory is open ended toward improvements in the electron-electron interaction operator. It is demonstrated that relativistic effects are substantial for the L -edge spectrum of sulfur, and substantial deviations from the statistical 2:1 spin-orbit splitting of the intensity distribution are found. The average ratio in the mixed region is 1.54 at the present level of theory.

  • 25. Ekström, U.
    et al.
    Norman, Patrick
    Linköping University, Sweden.
    Rizzo, A.
    Four-component Hartree-Fock calculations of magnetic-field induced circular birefringence - Faraday effect - In noble gases and dihalogens2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 7, 074321Article in journal (Refereed)
    Abstract [en]

    The effects of relativity on the magnetic-field induced circular birefringence, or Faraday effect, in He, Ne, Ar, Xe, Rn, F 2, Cl 2, Br 2, and I 2 have been determined at the four-component Hartree-Fock level of theory. A measure of the birefringence is given by the Verdet constant, which is a third-order molecular property and thus relates to quadratic response functions. A fully analytical nonlinear polarization propagator approach is employed. The results are gauge invariant as a consequence of the spatial symmetries in the molecular systems. The calculations include electronic as well as vibrational contributions to the property. Comparison with experiment is made for He, Ne, Ar, Xe, and Cl 2, and, apart from neon, the theoretical values of the Verdet constant are within 10% of the experimental ones. The inclusion of nonrelativistically spin-forbidden excitations in the propagator parametrization has significant effects on the dispersion in general, but such effects are in the general case largely explained by the use of a resonant-divergent propagator theory. In the present work we do, however, observe noticeable relativistic corrections to the Verdet constant in the off-resonant regions for systems with light elements (F 2 and Cl 2), and nonrelativistic results for the Verdet constant of Br 2 are in error by 25% in the low-frequency region.

  • 26. Ekström, U.
    et al.
    Ottosson, H.
    Norman, Patrick
    Linköping University, Sweden.
    Characterization of the chemisorption of methylsilane on a au(1,1,1) surface from the silicon K- And L-edge spectra: A theoretical study using the four-component static exchange approximation2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 37, 13846-13850 p.Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) of methylsilane, isolated and chemisorbed to a Au(1,1,1) surface, are determined in the fully relativistic four-component static exchange approximation - both the K- and the L-edge of silicon are addressed in this investigation. In the fully chemisorbed structure, three H(Si) atoms have been cleaved off when Si binds in the hollow site of Au forming three Si - Au bonds of normal length. As due to die tri-coordinated chemisorption, the onsets of the K- and L-edge NEXAFS absorption bands occur some 2.0 and 2.5 eV lower in energy, respectively. The spin-orbit splittings in the silicon 2p-shell are not significantly changed due to adsorption. A partly chemisorbed methylsilane with only one H(Si) bond cleaved was also studied, and it is shown that the polarization dependence in the surface spectra contains details that can be used experimentally to identify the surface coordination of silicon. The red-shifts in the XPS silicon 1s (2p) spectra upon surface binding are 0.95 (0.65) and 1.15 (0.83) eV for the mono- and tricoordinated system, respectively.

  • 27. Ekström, Ulf
    et al.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH.
    Carravetta, Vincenzo
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Polarization propagator for X-ray spectra2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 14Article in journal (Refereed)
    Abstract [en]

    A polarization propagator for x-ray spectra is outlined and implemented in density functional theory. It rests on a formulation of a resonant-convergent first-order polarization propagator approach which 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 spectrum relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects.

  • 28. Elm, J.
    et al.
    Norman, P.
    Bilde, M.
    Mikkelsen, K. V.
    Computational study of the Rayleigh light scattering properties of atmospheric pre-nucleation clusters2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 22, 10883-10890 p.Article in journal (Refereed)
    Abstract [en]

    The Rayleigh and hyper Rayleigh scattering properties of the binary (H 2SO4)(H2O)n and ternary (H 2SO4)(NH3)(H2O)n clusters are investigated using a quantum mechanical response theory approach. The molecular Rayleigh scattering intensities are expressed using the dipole polarizability α and hyperpolarizability β tensors. Using density functional theory, we elucidate the effect of cluster morphology on the scattering properties using a combinatorial sampling approach. We find that the Rayleigh scattering intensity depends quadratically on the number of water molecules in the cluster and that a single ammonia molecule is able to induce a high anisotropy, which further increases the scattering intensity. The hyper Rayleigh scattering activities are found to be extremely low. This study presents the first attempt to map the scattering of atmospheric molecular clusters using a bottom-up approach. This journal is © the Partner Organisations 2014.

  • 29. Elm, J.
    et al.
    Norman, P.
    Mikkelsen, K. V.
    Rayleigh light scattering properties of atmospheric molecular clusters consisting of sulfuric acid and bases2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 24, 15701-15709 p.Article in journal (Refereed)
    Abstract [en]

    The Rayleigh light scattering properties of (H<inf>2</inf>SO<inf>4</inf>)<inf>a</inf>(NH<inf>3</inf>)<inf>b</inf> and (H<inf>2</inf>SO<inf>4</inf>)<inf>a</inf>((CH<inf>3</inf>)<inf>2</inf>NH)<inf>b</inf> atmospheric molecular clusters have been investigated using a response theory approach. Using density functional theory the molecular structures and stepwise formation free energies of clusters with a and b up to 4 have been re-investigated. The Rayleigh scattering intensities are calculated from the dipole polarizability tensor α using the CAM-B3LYP functional by applying linear response methods. The intrinsic scattering properties of (H<inf>2</inf>SO<inf>4</inf>)<inf>a</inf>(NH<inf>3</inf>)<inf>b</inf> and (H<inf>2</inf>SO<inf>4</inf>)<inf>a</inf>((CH<inf>3</inf>)<inf>2</inf>NH)<inf>b</inf> indicate that amine containing clusters scatter light significantly more efficiently then their ammonia containing counterparts. Using the Atmospheric Cluster Dynamics Code (ACDC) the steady state cluster concentrations are estimated and the effective scattering is calculated. The effective scattering is shown to be highly dependent on the estimated concentrations and indicates that there exist competitive pathways, such as nucleation and coagulation, which influence the cluster distributions. The frequency dependence of the scattering is found to depend on the cluster composition and show increased responses when clusters contain more bases than acid molecules. Based on structures obtained using semi-empirical molecular dynamics simulations the Rayleigh scattering properties of clusters with up to 20 acid-base pairs are evaluated. This study represents the first step towards gaining a fundamental understanding of the scattering properties of small atmospheric clusters in the ambient atmosphere. © the Owner Societies 2015.

  • 30. Fahleson, T.
    et al.
    Kauczor, J.
    Norman, P.
    Coriani, S.
    The magnetic circular dichroism spectrum of the C 60 fullerene2013In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 111, no 9-11, 1401-1404 p.Article in journal (Refereed)
    Abstract [en]

    The magnetic circular dichroism spectrum of the C60 fullerene has been determined with the use of Kohn-Sham density functional theory in conjunction with the CAM-B3LYP exchange-correlation functional. The experimental spectrum of Gasyna et al. [Chem. Phys. Lett. 183, 283 (1991)] covering the wavelength region above 200 nm is explained by the signal responses from the three lowest singlet states of T 1u symmetry. © 2013 Copyright Taylor and Francis Group, LLC.

  • 31. Fahleson, T.
    et al.
    Kauczor, J.
    Norman, P.
    Santoro, F.
    Improta, R.
    Coriani, S.
    TD-DFT investigation of the magnetic circular dichroism spectra of some purine and pyrimidine bases of nucleic acids2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 21, 5476-5489 p.Article in journal (Refereed)
    Abstract [en]

    We present a computational study of the magnetic circular dichroism (MCD) spectra in the 200-300 nm wavelength region of purine and its derivative hypoxanthine, as well as of the pyrimidine bases of nucleic acids uracil, thymine, and cytosine, using the B3LYP and CAM-B3LYP functionals. Solvent effects are investigated within the polarizable continuum model and by inclusion of explicit water molecules. In general, the computed spectra are found to be in good agreement with the experimental ones, apart from some overall blue shifts. Both the pseudo-A term shape of the MCD spectra of the purines and the B term shape of the spectra of pyrimidine bases are reproduced. Our calculations also correctly reproduce the reversed phase of the MCD bands in purine compared to that of its derivatives present in nucleic acids. Solvent effects are sizable and system specific, but they do not in general alter the qualitative shape of the spectra. The bands are dominated by the bright π → π∗ transitions, and our calculations in solution nicely reproduce their energy differences, improving the estimates obtained in the gas phase. Shoulders are predicted for purine and uracil due to n → π∗ excitations, but they are too weak to be observed in the experiment. © 2015 American Chemical Society.

  • 32. Fahleson, T.
    et al.
    Norman, P.
    Coriani, S.
    Rizzo, A.
    Rikken, G. L. J. A.
    A density functional theory study of magneto-electric Jones birefringence of noble gases, furan homologues, and mono-substituted benzenes2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, no 19, 194311Article in journal (Refereed)
    Abstract [en]

    We report on the results of a systematic ab initio study of the Jones birefringence of noble gases, of furan homologues, and of monosubstituted benzenes, in the gas phase, with the aim of analyzing the behavior and the trends within a list of systems of varying size and complexity, and of identifying candidates for a combined experimental/theoretical study of the effect. We resort here to analytic linear and nonlinear response functions in the framework of time-dependent density functional theory. A correlation is made between the observable (the Jones constant) and the atomic radius for noble gases, or the permanent electric dipole and a structure/chemical reactivity descriptor as the para Hammett constant for substituted benzenes. © 2013 AIP Publishing LLC.

  • 33.
    Fahleson, Tobias
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Resonant-convergent second-order nonlinear response functions at the levels of Hartree-Fock and Kohn-Sham density functional theory2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 14, 144109Article in journal (Refereed)
    Abstract [en]

    The second-order nonlinear (or cubic) response function is derived from the Ehrenfest theorem with inclusion made of the finite lifetimes of the excited states, representing the extension of the derivation of the quadratic response function in the same framework [P. Norman et al., J. Chem. Phys. 123, 194103 (2005)]. The resulting damped response functions are physically sound and converging also in near-resonance and resonance regions of the spectrum. Being an accurate approximation for small complex frequencies (defined as the sum of an optical frequency and an imaginary damping parameter), the polynomial expansion of the complex cubic response function in terms of the said frequencies is presented and used to validate the program implementation. In terms of approximate state theory, the computationally tractable expressions of the damped cubic response function are derived and implemented at the levels of Hartree-Fock and Kohn-Sham density functional theory. Numerical examples are provided in terms of studies of the intensity-dependent refractive index of para-nitroaniline and the two-photon absorption cross section of neon. For the latter property, a numerical comparison is made against calculations of the square of two-photon matrix elements that are identified from a residue analysis of the resonance-divergent quadratic response function.

  • 34. Fahleson, Tobias
    et al.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Linköping University, Sweden.
    A Polarization Propagator for Nonlinear X-ray Spectroscopies2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 11, 1991-1995 p.Article in journal (Refereed)
    Abstract [en]

    A complex polarization propagator approach has been developed to third order and implemented in density functional theory (DFT), allowing for the direct calculation of nonlinear molecular properties in the X-ray wavelength regime without explicitly addressing the excited-state manifold. We demonstrate the utility of this propagator method for the modeling of coherent near-edge X-ray two-photon absorption using, as an example, DFT as the underlying electronic structure model. Results are compared with the corresponding near edge X-ray absorption fine structure spectra, illuminating the differences in the role of symmetry, localization, and correlation between the two spectroscopies. The ramifications of this new technique for nonlinear X-ray research are briefly discussed.

  • 35. Falklöf, O.
    et al.
    Durbeej, B.
    Norman, Patrick
    Linköping University, Sweden.
    Inter-Excited-State Phosphorescence in the Four-Component Relativistic Kohn-Sham Approximation: A Case Study on Lumiflavin2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 49, 11911-11921 p.Article in journal (Refereed)
    Abstract [en]

    Electronic transitions from one excited state to another excited state of different spin symmetry play important roles in many biochemical reactions. Although recent years have seen much progress in the elucidation of nonradiative (intersystem crossing) relaxation mechanisms for such transitions, there is presently a scarcity of data available to assess whether also radiative (phosphorescence) mechanisms are relevant for these processes. Here, we demonstrate that the well-established ability of quantum chemical methods to describe intersystem crossing events between excited states can be supplemented by the ability to also describe inter-excited-state phosphorescence. Specifically, by performing four-component relativistic time-dependent density functional theory calculations, we obtain rate constants for the radiative transitions from the absorbing 1(πHπL∗) singlet state of lumiflavin to the 3(πHπL∗), 3(nN2πL∗), and 3(πH-1πL∗) triplet states, and subsequently, we compare these results with rate constants calculated for the corresponding nonradiative transitions. Thereby, it is found that the radiative rate constants for these particular transitions are typically 2 to 5 orders of magnitude smaller than the nonradiative ones.

  • 36. Fransson, T.
    et al.
    Burdakova, D.
    Norman, Patrick
    Linköping University, Sweden.
    K- and L-edge X-ray absorption spectrum calculations of closed-shell carbon, silicon, germanium, and sulfur compounds using damped four-component density functional response theory2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 19, 13591-13603 p.Article in journal (Refereed)
    Abstract [en]

    X-ray absorption spectra of carbon, silicon, germanium, and sulfur compounds have been investigated by means of damped four-component density functional response theory. It is demonstrated that a reliable description of relativistic effects is obtained at both K- and L-edges. Notably, an excellent agreement with experimental results is obtained for L2,3-spectra - with spin-orbit effects well accounted for - also in cases when the experimental intensity ratio deviates from the statistical one of 2:1. The theoretical results are consistent with calculations using standard response theory as well as recently reported real-time propagation methods in time-dependent density functional theory, and the virtues of different approaches are discussed. As compared to silane and silicon tetrachloride, an anomalous error in the absolute energy is reported for the L2,3-spectrum of silicon tetrafluoride, amounting to an additional spectral shift of ∼1 eV. This anomaly is also observed for other exchange-correlation functionals, but it is seen neither at other silicon edges nor at the carbon K-edge of fluorine derivatives of ethene. Considering the series of molecules SiH4-XFX with X = 1, 2, 3, 4, a gradual divergence from interpolated experimental ionization potentials is observed at the level of Kohn-Sham density functional theory (DFT), and to a smaller extent with the use of Hartree-Fock. This anomalous error is thus attributed partly to difficulties in correctly emulating the electronic structure effects imposed by the very electronegative fluorines, and partly due to inconsistencies in the spurious electron self-repulsion in DFT. Substitution with one, or possibly two, fluorine atoms is estimated to yield small enough errors to allow for reliable interpretations and predictions of L2,3-spectra of more complex and extended silicon-based systems.

  • 37. Fransson, T.
    et al.
    Coriani, S.
    Christiansen, O.
    Norman, Patrick
    Linköping University, Sweden.
    Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 12, 124311Article in journal (Refereed)
    Abstract [en]

    Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger π-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to π-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate π-peak separations due to spectral compressions, a characteristic which is inherent to this method.

  • 38. Fransson, T.
    et al.
    Saue, T.
    Norman, Patrick
    Linköping University, Sweden.
    Four-Component Damped Density Functional Response Theory Study of UV/Vis Absorption Spectra and Phosphorescence Parameters of Group 12 Metal-Substituted Porphyrins2016In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 12, no 5, 2324-2334 p.Article in journal (Refereed)
    Abstract [en]

    The influences of group 12 (Zn, Cd, Hg) metal-substitution on the valence spectra and phosphorescence parameters of porphyrins (P) have been investigated in a relativistic setting. In order to obtain valence spectra, this study reports the first application of the damped linear response function, or complex polarization propagator, in the four-component density functional theory framework [as formulated in Villaume et al. J. Chem. Phys. 2010, 133, 064105 ]. It is shown that the steep increase in the density of states as due to the inclusion of spin-orbit coupling yields only minor changes in overall computational costs involved with the solution of the set of linear response equations. Comparing single-frequency to multifrequency spectral calculations, it is noted that the number of iterations in the iterative linear equation solver per frequency grid-point decreases monotonously from 30 to 0.74 as the number of frequency points goes from one to 19. The main heavy-atom effect on the UV/vis-absorption spectra is indirect and attributed to the change of point group symmetry due to metal-substitution, and it is noted that substitutions using heavier atoms yield small red-shifts of the intense Soret-band. Concerning phosphorescence parameters, the adoption of a four-component relativistic setting enables the calculation of such properties at a linear order of response theory, and any higher-order response functions do not need to be considered-a real, conventional, form of linear response theory has been used for the calculation of these parameters. For the substituted porphyrins, electronic coupling between the lowest triplet states is strong and results in theoretical estimates of lifetimes that are sensitive to the wave function and electron density parametrization. With this in mind, we report our best estimates of the phosphorescence lifetimes to be 460, 13.8, 11.2, and 0.00155 s for H2P, ZnP, CdP, and HgP, respectively, with the corresponding transition energies being equal to 1.46, 1.50, 1.38, and 0.89 eV.

  • 39. Fransson, T.
    et al.
    Zhovtobriukh, I.
    Coriani, S.
    Wikfeldt, K. T.
    Norman, Patrick
    Linköping University, Sweden.
    Pettersson, L. G. M.
    Requirements of first-principles calculations of X-ray absorption spectra of liquid water2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, 566-583 p.Article in journal (Refereed)
    Abstract [en]

    A computational benchmark study on X-ray absorption spectra of water has been performed by means of transition-potential density functional theory (TP-DFT), damped time-dependent density functional theory (TDDFT), and damped coupled cluster (CC) linear response theory. For liquid water, using TDDFT with a tailored CAM-B3LYP functional and a polarizable embedding, we find that an embedding with over 2000 water molecules is required to fully converge spectral features for individual molecules, but a substantially smaller embedding can be used within averaging schemes. TP-DFT and TDDFT calculations on 100 MD structures demonstrate that TDDFT produces a spectrum with spectral features in good agreement with experiment, while it is more difficult to fully resolve the spectral features in the TP-DFT spectrum. Similar trends were also observed for calculations of bulk ice. In order to further establish the performance of these methods, small water clusters have been considered also at the CC2 and CCSD levels of theory. Issues regarding the basis set requirements for spectrum simulations of liquid water and the determination of gas-phase ionization potentials are also discussed.

  • 40. Fransson, Thomas
    et al.
    Rehn, Dirk Robert
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Dreuw, Andreas
    Norman, P.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Static polarizabilities and C-6 dispersion coefficients using the algebraic-diagrammatic construction scheme for the complex polarization propagator2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 9, 094301Article in journal (Refereed)
    Abstract [en]

    An implementation of the damped linear response function, or complex polarization propagator, using the algebraic-diagrammatic construction (ADC) scheme has been developed and utilized for the calculation of electric-dipole polarizabilities and C-6 dispersion coefficients. Four noble gases (He, Ne, Ar, and Kr), five n-alkanes (methane, ethane, propane, butane, and pentane), three carbonyls (formaldehyde, acetaldehyde, and acetone), and three unsaturated hydrocarbons (ethene, acetylene, and benzene) have been treated with the hierarchical set of models ADC(2), ADC(2)-x, and ADC(3/2), and comparison has been made to results obtained with damped linear response Hartree-Fock (HF) and coupled cluster singles and doubles (CCSD) theory as well as high-quality experimental estimates via the dipole oscillator strength distribution approach. This study marks the first ADC calculations of C-6 dispersion coefficients and the first ADC(3/2) calculations of static polarizabilities. Results at CCSD and ADC(3/2) levels of theory are shown to be of similar quality, with electron correlation effects increasing the molecular property values for all calculations except CCSD considerations of ethene and acetylene (attributed to an overestimation of bond electron density at HF level of theory). The discrepancies betweenCCSDand ADC(3/2) are partially due toADCoverestimating anisotropies, and discrepancies with respect to experimental values are partially due to the lack of zero-point vibrational effects in the present study.

  • 41. Glimsdal, E.
    et al.
    Norman, Patrick
    Linköping University, Sweden.
    Lindgren, M.
    Excitation and emission properties of platinum(II) acetylides at high and low concentrations2009In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 113, no 42, 11242-11249 p.Article in journal (Refereed)
    Abstract [en]

    Photophysical properties of platinum(II) acetylides in tetrahydrofuran (THF) solutions and incorporated in poly (methyl methacrylate) (PMMA) glasses have been studied over a large concentration range from 10 /ÀM to 50 mM. In general, the luminescence properties of the studied chromophores in the liquid state were also maintained in the solid state, except for shorter decay times of 50-90 μs of the triplet state in the glass compared with 200-300 μs in solution at low concentrations. The phosphorescence line shapes were found to be independent of both the chromophore concentration and the environment (THF and PMMA). The triplet state lifetimes did not change with concentration in the solid-state case, whereas, in solution, the decay becomes shorter at increasing concentration. The latter effect could be modeled with an additional linear quenching rate, kq in the range of (1 to 7) × 107 M-1 s-1. Excitation spectra of the triplet state at high concentrations, in both solutions and solid glasses, showed additional excitation bands on the long wavelength side compared with the corresponding measurements at low concentrations. This indicates enhanced singlet-triplet coupling due to intermolecular electronic interactions that become important at concentrations of 0.1 to 1 mM and above.

  • 42. Henriksson, J.
    et al.
    Ekström, U.
    Norman, P.
    On the evaluation of quadratic response functions at the four-component Hartree-Fock level: Nonlinear polarization and two-photon absorption in bromo- and iodobenzene2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 21, 214311Article in journal (Refereed)
    Abstract [en]

    The nonlinear polarization and two-photon absorption parameters have been determined for dibromo- and di-iodobenzene in their meta- and ortho-conformations and with relativistic effects accounted for to a varying degree. By exclusion of small component integrals in the calculations of the first-order hyperpolarizability, results within 1% of fully relativistic four-component Hartree-Fock values are obtained at a cost of 8.7 times the corresponding nonrelativistic calculations. It is shown that the nonlinear absorption in bromobenzene (and even more so in iodobenzene) is broad banded due to spin-orbit interactions among the excited states, and nonrelativistic and scalar relativistic calculations are not to be used in this case. © 2006 American Institute of Physics.

  • 43. Henriksson, J.
    et al.
    Norman, Patrick
    Linkoping University, Sweden.
    Jensen, H. J. A.
    Two-photon absorption in the relativistic four-component Hartree-Fock approximation2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 11, 114106Article in journal (Refereed)
    Abstract [en]

    A first implementation of the single residue of the quadratic response function in the four-component Hartree-Fock approximation is presented. The implementation is based on a Kramers paired molecular orbital basis and takes full advantage of time and spatial symmetry reductions in a quaternion formulation-in analogy with the previous work on the quadratic response function [J. Chem. Phys. 121, 6145 (2004)]. Sample calculations are given in terms of the monochromatic and coherent two-photon absorption cross sections in the noble gases. The relativistic two-photon selection rule ΔJ= {0,±2} allows for nonrelativistically spin-forbidden transitions, and, even in neon, strong two-photon absorption is shown to occur for the X S01 →2 P23 transition. It is argued that relevant comparisons between nonrelativistic and relativistic calculations must be performed at the level of integrated absorption cross sections.

  • 44. Henriksson, J.
    et al.
    Saue, T.
    Norman, Patrick
    Linkopings universitet, Sweden.
    Quadratic response functions in the relativistic four-component Kohn-Sham approximation2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 2, 024105Article in journal (Refereed)
    Abstract [en]

    A formulation and implementation of the quadratic response function in the adiabatic four-component Kohn-Sham approximation is presented. The noninteracting reference state is time-reversal symmetric and formed from Kramers pair spinors, and the energy density is gradient corrected. Example calculations are presented for the optical properties of disubstituted halobenzenes in their meta and ortho conformations. It is demonstrated that correlation and relativistic effects are not additive, and it is shown that relativity alone reduces the μ Β- -response signal by 62% and 75% for meta- and ortho-bromobenzene, respectively, and enhances the same response by 17% and 21% for meta- and ortho-iodobenzene, respectively. Of the employed functionals, CAM-B3LYP shows the best performance and gives hyperpolarizabilities Β distinctly different from B3LYP.

  • 45. Henriksson, Johan
    et al.
    Nyrell, Susanna
    Norman, Patrick
    Linkoping University, Sweden.
    Theoretical Design of Optical Switches Using the Spin Transition Phenomenon2006In: Computing letters, ISSN 1574-0404, Vol. 2, no 4, 237-249 p.Article in journal (Refereed)
    Abstract [en]

    The spin characteristics of octahedrically coordinated Fe(II) compounds are determined from first-principles quantum chemical calculations. Four novel Fe(II) spin transition materials are suggested for use in optical switching applications.

  • 46.
    Holmgaard List, Nanna
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Knoops, Jeremie
    Rubio-Magnieto, Jenifer
    Ide, Julien
    Beljonne, David
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Surin, Mathieu
    Linares, Mathieu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Origin of DNA-Induced Circular Dichroism in a Minor-Groove Binder2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 42, 14947-14953 p.Article in journal (Refereed)
    Abstract [en]

    Induced circular dichroism (ICD) of DNA-binding ligands is well known to be strongly influenced by the specific mode of binding, but the relative importance of the possible mechanisms has remained undetermined. With a combination of molecular dynamics simulations, CD response calculations, and experiments on an AT-sequence, we show that the ICD of minor-groove-bound 4',6-diamidino-2-phenylindole (DAPI) originates from an intricate interplay between the chiral imprint of DNA, off-resonant excitonic coupling to nucleobases, charge-transfer, and resonant excitonic coupling between DAPIs. The significant contributions from charge-transfer and the chiral imprint to the ICD demonstrate the inadequacy of a standard Frenkel exciton theory of the DAPI-DNA interactions.

  • 47.
    Holmgaard List, Nanna
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Kongsted, J.
    Jensen, H. J
    A quantum-mechanical perspective on linear response theory within polarizable embedding2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 23, 234101Article in journal (Refereed)
    Abstract [en]

    We present a derivation of linear response theory within polarizable embedding starting from a rigorous quantum-mechanical treatment of a composite system. To this aim, two different subsystem decompositions (symmetric and nonsymmetric) of the linear response function are introduced and the pole structures as well as residues of the individual terms are discussed. In addition to providing a thorough justification for the descriptions used in polarizable embedding models, this theoretical analysis clarifies which form of the response function to use and highlights complications in separating out subsystem contributions to molecular properties. The basic features of the presented expressions and various approximate forms are illustrated by their application to a composite model system.

  • 48. Hülsen, M.
    et al.
    Norman, P.
    Dolg, M.
    Theoretical investigation of thermally and photochemically induced haptotropic rearrangements of chromium ligands on naphthalene systems2011In: Journal of Organometallic Chemistry, ISSN 0022-328X, E-ISSN 1872-8561, Vol. 696, no 24, 3861-3866 p.Article in journal (Refereed)
    Abstract [en]

    The description of chemical reactions by means of quantum mechanical methods is an important task and gets even more challenging if excited states have to be considered. This work focuses on the haptotropic rearrangements of chromium atoms bearing three coligands which migrate on a naphthalene-like system. The reactions are either thermally or photochemically controllable and thus the systems are candidates for molecular switches. We propose a detailed reaction scheme for the investigated system. Furthermore, we provide a detailed analysis of the important steps of the reaction cycle. In comparison to previous publications, the scope of this work also involves the quantum mechanical treatment of excited states in order to describe occurring photon absorption processes in a proper way. Linear response time-dependent density functional theory calculations were carried out to describe the molecules' responses to the external electromagnetic perturbations. © 2011 Elsevier B.V. All rights reserved.

  • 49. Jansik, B.
    et al.
    Schimmelpfennig, B.
    Norman, P.
    Macak, P.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Ohta, K.
    Relativistic effects on linear and non-linear polarizabilities of the furan homologues2003In: Journal of Molecular Structure: THEOCHEM, ISSN 0166-1280, Vol. 633, no 03-feb, 237-246 p.Article in journal (Refereed)
    Abstract [en]

    First principles calculations including relativistic effects are carried out for dipole moments, polarizabilities, first- and second-order hyperpolarizabilities for the series of furan homologues XC4H4, X = O, S, Se, Te, at three different levels of theory; time-dependent Dirac-Hartree-Fock (DHF), time-dependent Hartree-Fock with a Douglas-Kroll transformed one-component Hamiltonian, and time-dependent Hartree-Fock using effective-core potentials. By comparison with the corresponding non-relativistic results, the influence of relativistic effects on the properties as well as the accuracy of previously reported calculations on these molecules using effective-core potentials for selenium and tellurium can be addressed. The obtained results indicate that relativistic effects can be described with comparable accuracy at all three employed levels, and that non-scalar effects, which are explicitly treated only at the time-dependent DHF level, are of minor importance. Frequency dispersion and relativity are found to be additive at the single-determinant level. We find that relativistic effects cannot make up for the earlier identified mismatch between theory and experiment for the non-linear polarizabilities of the heavier homologues. A Bishop-Kirtman analysis of vibrational effects indicates that the same can be said about these.

  • 50. Jansik, B.
    et al.
    Schimmelpfennig, B.
    Norman, P.
    Mochizuki, Y.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Size, order, and dimensional relations for silicon cluster polarizabilities2002In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 106, no 2, 395-399 p.Article in journal (Refereed)
    Abstract [en]

    Response theory calculations in the random phase approximation are applied to linear polarizabilities and second hyperpolarizabilities of 1-, 2-, and 3-dimensional hydrogen-terminated silicon clusters. Successive enlargement of the clusters to embody on the order of 50 silicon atoms plus bond-saturating hydrogen atoms allows for extrapolation to bulk values of individual silicon atom contributions in the 1D and 3D cases. Modern effective core potentials are shown to provide excellent approximations to the all-electron values in all cases; errors for both polarizabilities and hyperpolarizabilities are on the order of 1%. The findings indicate considerable time savings in predictions of the electric polarizability properties of elements beyond the first row atoms.

1234 1 - 50 of 171
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf