Ändra sökning
Avgränsa sökresultatet
123 1 - 50 av 116
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1. Aaboud, M.
    et al.
    Kastanas, Konstatinos A.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ohm, Christian
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ripellino, Giulia
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    L.Zwalinski,
    et. al.,
    Search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a Z boson in pp collisions at s=13 TeV with the ATLAS detector2018Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 776, s. 318-337Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a leptonically decaying Z boson in proton–proton collisions at s=13 TeV is presented. This search uses 36.1 fb−1 of data collected by the ATLAS experiment at the Large Hadron Collider. No significant deviation from the expectation of the Standard Model backgrounds is observed. Assuming the Standard Model ZH production cross-section, an observed (expected) upper limit of 67% (39%) at the 95% confidence level is set on the branching ratio of invisible decays of the Higgs boson with mass mH=125 GeV. The corresponding limits on the production cross-section of the ZH process with the invisible Higgs boson decays are also presented. Furthermore, exclusion limits on the dark matter candidate and mediator masses are reported in the framework of simplified dark matter models. 

  • 2. Aaboud, M.
    et al.
    Kastanas, Konstatinos A.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ohm, Christian
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ripellino, Giulia
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Zwalinski, L.
    et.al.,
    Measurement of differential cross sections of isolated-photon plus heavy-flavour jet production in pp collisions at s=8 TeV using the ATLAS detector2018Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, s. 295-317Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton–proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb−1. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: |ηγ|<1.37 and 1.56<|ηγ|<2.37. The measurement covers photon transverse energies 25<ET γ<400 GeV and 25<ET γ<350 GeV respectively for the two |ηγ| regions. For each jet flavour, the ratio of the cross sections in the two |ηγ| regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central γ+b measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.

  • 3.
    Baryshnikov, Glib V.
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. V. D. Kuznetsov Siberian Physical-Technical Institute at National Research Tomsk State University, Russian Federation.
    Minaev, Boris F.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. V. D. Kuznetsov Siberian Physical-Technical Institute at National Research Tomsk State University, Russian Federation.
    Baryshnikova, A. A.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Anion-induced exchange interactions in binuclear complexes of Cu(II) with flexible hexadentate bispicolylamidrazone ligands2016Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 661, s. 48-52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two recently synthesized copper(II) complexes with spacer-armed bispicolylamidrazone ligands have been theoretically studied at the density functional theory (DFT) level accounting for empirical dispersion correction and intrinsic anionic environment by perchlorate ions. The exchange parameter between the open-shell singlet and triplet states of the studied complexes has been estimated by broken symmetry DFT calculations. The mechanism of spin-spin exchange interaction between the unpaired electrons via the σ-bond aliphatic chain (Gusev et al., 2015) is confirmed. Instead, a anion-induced mechanism is proposed which means that the anionic grid participates in the exchange interaction between the unpaired electrons.

  • 4. Baudin, M.
    et al.
    Wojcik, M.
    Hermansson, Kersti
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Palmqvist, A. E. C.
    Muhammed, Mamoun
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    MD simulations of a doped ceria surface - very large surface ion motion2001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 335, nr 06-maj, s. 517-523Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mean-square displacements (MSDs) and individual-ion square-displacements (ISDs) for the different constituents in Ca-doped CeO2(0 1 1) slabs at 300 K have been studied as a function of depth from the surface. Constant pressure-constant temperature MD simulations were used. The MSDs are 2-3 times larger at the surface than in the bulk, but ISDs as large as ca. 150 times the surface MSD value were observed during short-time periods for anions next to an anion vacancy at the surface. The chemical implications of this kind of motion are important, since transient structural distortions of this magnitude will lead to large electron re-distributions.

  • 5. Bauer, C.
    et al.
    Boschloo, Gerrit
    Mukhtar, E.
    Hagfeldt, A.
    Ultrafast relaxation dynamics of charge carriers relaxation in ZnO nanocrystalline thin films2004Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 387, nr 03-jan, s. 176-181Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ultrafast spectroscopy has been used to study the relaxation processes of charge carriers in ZnO nanocrystalline thin films. A broad red-IR absorption band linked to shallowly trapped electrons was observed by spectroelectrochemical measurements. Femtosecond transient absorption data revealed multiexponential decays of the charge carriers with time constants ranging from 1 to 400 ps. The decay profile of the signal shows a probe wavelength dependence. This effect is assigned to the trapping (localisation) of nonequilibrium charge carriers which occurs on a time scale of similar to1 ps. The recombination of shallowly trapped electrons with deeply trapped holes, determined by single-photon counting, mainly occurs in 400 ps.

  • 6. Belyanin, Maxim L.
    et al.
    Stepanova, Elena V.
    Valiev, Rashid R.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. National Research Tomsk Polytechnic University, Russian Federation.
    Filimonov, Victor D.
    Usov, Vladimir Y.
    Borodin, Oleg Y.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Design, synthesis and evaluation of a new Mn - Contrast agent for MR imaging of myocardium based on the DTPA-phenylpentadecanoic acid complex2016Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 665, s. 111-116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present paper we describe the first synthesis and evaluation of a novel Mn (II) complex (DTPA-PPDA Mn (II)) which contains a C-15 fatty acid moiety that has high affinity to the heart muscle. The complexation energy of DTPA-PPDA Mn (II) evaluated by quantum chemistry methodology indicates that it essentially exceeds the corresponding value for the known DTPA Mn (II) complex. Molecular docking revealed that the affinity of the designed complex to the heart-type transport protein H-FABP well exceeds that of lauric acid. Phantom experiments in low-field MRI the designed contrast agent provides MR imaging comparable to gadopentetic acid.

  • 7. Birgerson, J.
    et al.
    Keil, M.
    Luo, Yi
    KTH, Tidigare Institutioner, Bioteknologi.
    Svensson, S.
    Ågren, Hans
    KTH, Tidigare Institutioner, Bioteknologi.
    Salaneck, W. R.
    A study of the electronic structure of ethylenedioxythiophene in gas phase using NEXAFS and quantum chemical calculations2004Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 392, nr 1-3, s. 100-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Near-edge X-ray absorption fine structure spectroscopy spectra of ethylenedioxythiophene has been recorded in gas phase at the carbon K-edge, sulphur L-edge and oxygen, K-edge. The experimental data has been interpreted with the help of a modified density functional code deMon. The good agreement between the calculated spectra and the measured one allows us to assign all observed resonances. The existence of pi* resonances in both the measured and the calculated OK-edge adsorption spectrum demonstrate that the delocalized pi-system of the thiophene part of the molecule is extended up to the oxygen atoms of the molecule.

  • 8. Bittererova, M.
    et al.
    Brinck, Tore
    KTH, Tidigare Institutioner                               , Kemi.
    Ostmark, H.
    Theoretical study of the singlet electronically excited states of N-42001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 340, nr 06-maj, s. 597-603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vertical excitation energies for the lowest eleven singlet states of T-d N-4 were calculated using the TD-DFT method with the B3LYP functional, and at the EOM-CCSD level of theory. The vertical excitation energies for the five lowest-lying excited states were also obtained using the state-averaged CASSCF, CASPT2, CASPT3, and MRCI + Q methods. Our results show that the five lowest-lying states are of valence character. EOM-CCSD/d-aug-cc-pVTZ calculations predict that there are two weakly allowed optical transitions of T-2 symmetry at 10.44 and 10.82 eV. The transition to the third T-2 state, which is predicted to be at 10.89 eV, has an oscillator strength about one order of magnitude higher.

  • 9. Bittererova, M.
    et al.
    Ostmark, H.
    Brinck, Tore
    KTH, Tidigare Institutioner                               , Kemi.
    Ab initio study of the ground state and the first excited state of the rectangular (D-2h) N-4 molecule2001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 347, nr 03-jan, s. 220-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dissociation pathway of D-2h N-4 has been investigated at the CASSCF level of theory. A new C-2v transition state to dissociation was found and characterized on the potential energy surface. The effective barrier of dissociation from D-2h N-4 to 2N(2) is estimated to 6.5 kcal/mol from MR-AQCCNTZ//CAS(12,12)/VTZ calculations. Vertical excitation energies and oscillator strengths for the lowest 20 singlet states of D-2h N-4 have been calculated using the EOM-CCSD method. The geometry of the first excited state B-1(3u), considered as the lowest optically accessible state, has been optimized and characterized at various computational levels. This state might be useful for detection of D-2h N-4 by means of laser-induced fluorescence (LIF) spectroscopy.

  • 10. Boschloo, Gerrit
    et al.
    Hagfeldt, A.
    Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO22003Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 370, nr 04-mar, s. 381-386Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Photoinduced absorption (PIA) spectroscopy was used to investigate dye-sensitized electrodes and solar cells under illumination conditions comparable to sunlight. In the absence of redox electrolyte, cis-Ru (dcbpy)(2)(NCS)(2)-sensitized nanostructured TiO2 films show a long-lived photoinduced charge-separation (oxidized dye molecules/injected electrons in TiO2), with a lifetime of about 10(-3) s under full sun illumination. The PIA spectrum of a complete dye-sensitized cell is due to electrons in TiO2 and iodine radicals (12) in the electrolyte. The lifetime of this charge-separated state at open-circuit conditions was determined to be 0.15 s (0.27 sun illumination).

  • 11. Carniato, S.
    et al.
    Taieeb, R.
    Guillemin, R.
    Journel, L.
    Simon, M.
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    K-L resonant X-ray Raman scattering as a tool for potential energy surface mapping2007Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 439, nr 06-apr, s. 402-406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With help of theoretical calculations, we demonstrate that original pump-probe experiments, using IR laser as a pump and K-L X-ray Raman scattering as a probe, offer a powerful tool to map core-excited potential energy curves with very high energy resolution, beyond vibrational and lifetime limitations.

  • 12. Carravetta, V.
    et al.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    An ab initio method for computing multi-atom resonant photoemission2002Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 354, nr 02-jan, s. 100-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an ab initio method for computing multi-atom resonant photoemission (MARPE) in molecules and use this method to investigate the possibility of having a sizable MARPE effect. The MARPE cross section is obtained by making multi-center expansions of both the dipole matrix element - direct emission - and the hamiltonian matrix element between the resonant state and the autoionizing states - resonant emission. We show by sample calculations that the resonant contribution exhibits a strong distance dependence of the atoms participating in the MARPE process, and that it is energy dependent and element specific for the neighboring atoms. The ratio of resonant MARPE and direct photoionization cross sections is found to amount to less than one percent which probably makes the molecular MARPE effect difficult to apply in practice.

  • 13. Cava, Carlos E.
    et al.
    Possagno, Ricardo
    Schnitzler, Mariane C.
    Roman, Paulo C.
    Oliveira, Marcela M.
    Lepiensky, Carlos M.
    Zarbin, Aldo J. G.
    Roman, Lucimara S.
    Iron- and iron oxide-filled multi-walled carbon nanotubes: Electrical properties and memory devices2007Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 444, nr 4-6, s. 304-308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrical and morphological properties of neat iron- and iron oxide-filled multi-walled carbon nanotubes and its dispersion with a semiconducting polymer were investigated. The electrical properties of these carbon nanotubes changed significantly when exposed to different atmospheres. The current voltage characteristics of the films formed from the dispersions were obtained from planar devices with metallic electrodes. These devices were used as gas sensor and as memory devices where the writing, reading and erasing can be done electrically.

  • 14.
    Chatterjee, S
    et al.
    Swiss Federal Institute for Materials Science and Technology, Empa.
    Wang, J.W.
    National Cheng Kung University, Taiwan.
    Kuo, W.S.
    Feng Chia University, Taiwan.
    Tai, N.H.
    National Tsing Hua University, Hsinchu, Taiwan.
    Salzmann, C.
    University College London, London, UK.
    Li, W.L.
    Hollertz, Rebecca
    Swiss Fed Labs Mat Sci & Technol Empa, Lab Funct Polymers, Switzerland.
    Nüesch, F.
    Chu, B.T.T.
    Mechanical reinforcement and thermal conductivity in expanded graphene nanoplatelets reinforced epoxy composites2012Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 531, s. 6-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Influence of reinforcements on mechanical and thermal properties of graphene nanoplatelets/epoxy composites is investigated. Amine functionalized expanded graphene nanoplatelets (EGNPs) were dispersed within epoxy resins using high-pressure processor followed by three roll milling. Functionality on the EGNPs was confirmed with FTIR and micro-Raman spectroscopy. Bending and nano-mechanical testing was performed on the composites. Incorporation of EGNPs improved the flexural modulus and hardness of the composite and increased fracture toughness by up to 60%. Marked improvement was observed in thermal conductivity of the composites reaching 36% at 2 wt.% loading. Functionalized EGNPs exhibited significant improvements indicating favorable interaction at EGNPs/polymer interface.

  • 15. Chattopadhyaya, Mausumi
    et al.
    Natarajan Arul, Murgan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Alam, Md. Mehboob
    Chakrabarti, Swapan
    Spatial spin-charge separation in neutral endohedral metallofullerene: A combined restricted open-shell MP2 and Car-Parrinello molecular dynamics study2013Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 557, s. 71-75Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first theoretical evidence of the unusual separation of spin and charge degrees of freedom of electron in a neutral endohedral metallofullerene, Sc@C-50. To demystify its origin, we have performed computation at the level of ROMP2 in combination with Car-Parrinello molecular dynamics at 300 K on a series of Sc@C-n. Our inspection reveals that a sharp fall of electron correlation in Sc@C-50 makes the system so sensitive that, to avoid additional Pauli repulsion, Sc leaves the charge component of the solitary 3d electron to C-50 keeping the spin density over its own.

  • 16.
    Chen, Tao
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Leiden Observatory, Leiden University, PO Box 9513, NL 2300 RA Leiden, The Netherlands.
    Zhen, J.
    Wang, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Linnartz, H.
    Tielens, A. G. G. M.
    From planes to bowls: Photodissociation of the bisanthenequinone cation2018Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 692, s. 298-303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a combined experimental and theoretical study of the photodissociation of the bisanthenequinone (C28H12O2) cation, Bq+. The experiments show that, upon photolysis, the Bq+ cation does not dehydrogenate, but instead fragments through the sequential loss of the two neutral carbonyl groups, causing the formation of five-membered carbon cycles. Quantum chemical calculations confirm this Bq+ → [Bq - CO]+ → [Bq - 2CO]+ sequence as the energetically most favorable reaction pathway. For the first CO loss, a transition state with a barrier of ∼3.2 eV is found, substantially lower than the lowest calculated H loss dissociation pathway (∼4.9 eV). A similar situation applies for the second CO loss channel (∼3.8 eV vs. ∼4.7 eV), but where the first dissociation step does not strongly alter the planar PAH geometry, the second step transforms the molecule into a bowl-shaped one. 

  • 17. Cronstrand, P.
    et al.
    Luo, Yi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Generalized few-state models for two-photon absorption of conjugated molecules2002Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 352, nr 04-mar, s. 262-269Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present three- and four-state models for two-photon absorption (TPA) cross-sections generalized to include dipolar direction information and polarization effects of the laser beam. By introducing an effective dipole moment which incorporates the directions of the transition dipole moments and the influence of additionally strongly coupled excited states we can distinguish between different effects leading to enhanced two-photon absorption.

  • 18.
    Cronstrand, Peter
    et al.
    KTH, Tidigare Institutioner, Bioteknologi.
    Luo, Yi
    KTH, Tidigare Institutioner, Bioteknologi.
    Norman, P.
    Ågren, Hans
    KTH, Tidigare Institutioner, Bioteknologi.
    Ab initio calculations of three-photon absorption2003Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 375, nr 02-jan, s. 233-239Artikel i tidskrift (Refereegranskat)
    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.
    de Almeida, Katia Júlia
    et al.
    Univ Fed Minas Gerais, Dept Quim.
    Cesar, Amary
    Univ Fed Minas Gerais, Dept Quim.
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Vahtras, Olav
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Modelling the visible absorption spectra of copper(II) acetylacetonate by density functional theory2010Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 492, nr 1-3, s. 14-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spin restricted open-shell Density Functional Theory calculations have been carried out by means of linear response theory to investigate the visible absorption spectrum of copper(II) acetylacetonate complex, Cu(acac)(2). The 3d -> 3d transition energies and the influence of molecular structure and non-coordinating solvent on the spectra have been investigated. The obtained four 3d -> 3d transition energies accord well with the experimental data in the crystal phase. The presented results indicate that the experimentally observed four band structure of Cu(acac)(2) is of molecular nature, and not caused by factor-group splitting in the crystal environment as previously suggested.

  • 20. Derkatch, A.
    et al.
    Lundevall, C.
    Berg, Lars-Erik
    KTH, Tidigare Institutioner                               , Fysik.
    Royen, P.
    Lifetime measurements of the A (2)Pi state of BaCl using laser spectroscopy2000Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 332, nr 04-mar, s. 278-282Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The lowest-lying radiative state of barium chloride has been studied by laser-induced fluorescence in the near-infrared wavelength region. The A (II1/2)-I-2 and A (II3/2)-I-2 states have been investigated in time-resolved experiments using a Ti:Sapphire laser. The zero pressure radiative lifetime measured for the e-levels of BaCl was 107 +/- 4 ns for the A (II1/2)-I-2 state and 101+/-6 ns for the A (II3/2)-I-2 state. The discrepancy between the corresponding transition moments is discussed.

  • 21. Dvinskikh, Sergey V.
    et al.
    Sandstrom, D.
    Zimmermann, H.
    Maliniak, A.
    C-13-detected H-1-H-2 separated local field NMR spectroscopy2003Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 382, nr 04-mar, s. 410-417Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new NMR method for measuring H-1-H-2 dipolar couplings in macroscopically oriented media. To overcome the lack of dipolar resolution in 1D H-1 and H-2 spectra of deuterated molecules, we use a 2D heteronuclear correlation experiment where H-1 chemical shifts and H-1-H-2 dipolar interactions in the first dimension are. correlated with C-13 chemical shifts and H-2-C-13 dipolar interactions in the second dimension. The technique is demonstrated on a columnar liquid-crystalline phase.

  • 22. Dvinskikh, Sergey V.
    et al.
    Yamamoto, K.
    Ramamoorthy, A.
    Separated local field NMR spectroscopy by windowless isotropic mixing2006Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 419, nr 03-jan, s. 168-173Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new separated local field NMR experiment, designed for accurate measurements of heteronuclear dipolar couplings, is described. The pulse sequence is based on a homonuclear decoupling windowless heteronuclear isotropic mixing approach to achieve the coherent polarization exchange between the z-components of the magnetizations in heteronuclear spin system. This technique suppresses chemical shifts and frequency offset variations irrespective of the dipolar coupling value. The experiment is demonstrated on a columnar liquid. crystal.

  • 23. Eden, M
    et al.
    Annersten, H
    Zazzi, Åsa
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Pulse-assisted homonuclear dipolar recoupling of half-integer quadrupolar spins in magic-angle spinning NMR2005Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 410, nr 1-3, s. 24-30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate numerically and experimentally that zero-quantum homonuclear dipolar recoupling techniques employing rotor-synchronized 180 degrees pulses, previously introduced for spin-1/2 applications, are useful also for magnetization transfers between half-integer quadrupolar nuclei in rotating solids. The recoupling sequences are incorporated as mixing periods in two-dimensional experimental protocols, that correlate either single-quantum coherences of coupled spins, or triple-quantum with single-quantum coherences for improving spectral resolution. We present Na-23 and Al-27 NMR experiments on powders of sodium sulphite [Na2SO3], YAG [Y3Al5O12] and a synthetic chlorite mineral [Mg4.5Al3Si2.5O10(OH)(8)].

  • 24. Engstrom, M.
    et al.
    Himo, Fahmi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ab initio g-tensor calculations of the thioether substituted tyrosyl radical in galactose oxidase2000Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 319, nr 04-mar, s. 191-196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The tyrosyl radical in galactose oxidase is covalently cross-linked to a neighboring cysteine residue through a thioether bond. The role of this sulfur cross-link has been discussed ever since the crystal structure of the enzyme was solved. In the present work, the ab initio multiconfigurational linear response method is applied to calculate the g-tensor of unsubstituted and thioether substituted phenoxyl radicals. In contrast to some previous interpretations, but in agreement with recent EPR measurements, we find that the sulfur substitution induces only minor shifts in the g-tensor components. The spin distribution retains the odd-alternant pattern of the unsubstituted radical and only a small amount of spin is localized to the sulfur center.

  • 25. Engstrom, M.
    et al.
    Vahtras, Olav
    KTH, Tidigare Institutioner, Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner, Bioteknologi.
    MCSCF and DFT calculations of EPR parameters of sulfur centered radicals2000Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 328, nr 06-apr, s. 483-491Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The EPR parameters of sulfur centered radicals are different depending on the radical structure, charge and solvent. That is, the g- and A-tensor components provide significant patterns which may distinguish sulfur radical structures from each other. In the present work, these EPR parameters were calculated for monosulfide radicals (RS'), disulfide radicals (RSS.), radical cations ((RSSR+)-S-.) and anions ((RSSR-)-S-.), with R = CH3, using the MCSCF linear response and DFT/B3LYP methods. Results were in agreement with experimental data for the cases when well-resolved EPR spectra are available. Especially, the assignment of the disulfide anion in ribonucleotide reductase was confirmed. The results indicate that investigations with the present computational methods on refined structures and solvent modeling may provide interpretations of experimental data on unassigned radical species.

  • 26. Engström, M.
    et al.
    Owenius, R.
    Vahtras, Olav
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ab initio g-tensor calculations of hydrogen bond effects on a nitroxide spin label2001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 338, nr 06-apr, s. 407-413Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydrogen bonding effects on the electron paramagnetic resonance (EPR) g-tensor of a nitroxide spin label was investigated by quantum chemical calculations. The restricted open-shell Hartree-Fock (ROHF) linear response method with the atomic mean field approximation (AMFI) was used in the calculations. The results show that hydrogen bonding reduces the g-tensor component directed along the NO bond, g(xx). This decrease is traced to higher excitation energy and lower spin-orbit coupling and angular momentum matrix elements for the n-pi* excitation. The calculations show that the g-tensor is practically invariable when hydrogen bonding was modeled with methanol instead of water.

  • 27. Feng, Yanli
    et al.
    Zhang, Qiong
    Tan, Wenjuan
    Zhang, Deqing
    Tu, Yaoquan
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Tian, He
    A supramolecular photoswitch constructed by intermolecular hydrogen bond between BTEPy and TTF-COOH2008Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 455, nr 4-6, s. 256-260Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel supramolecular photoswitch containing bisthienylethene- pyridine (BTEPy) and carboxyl attached tetrathiafluvalene (TTF-COOH) was constructed via intermolecular hydrogen bond. FT-IR spectra, XPS characterizations, H-1 NMR and theoretical calculation were carried out to verify the formation of the intermolecular hydrogen bond. The supramolecular self-assemblies BTEPy 2TTF show good photo-chromic properties. A molecular switch with UV/vis light as inputs and electrochemical signals as outputs was obtained.

  • 28. Ferrighi, Lara
    et al.
    Frediani, Luca
    Cappelli, Chiara
    Salek, Pawel
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Helgaker, Trygve
    Ruud, Kenneth
    Density-functional-theory study of the electric-field-induced second harmonic generation (EFISHG) of push-pull phenylpolyenes in solution2006Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 425, nr 4-6, s. 5593-5603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density-functional theory and the polarizable continuum model have been used to calculate the electric-field-induced second harmonic generation of a series of push-pull phenylpolyenes in chloroform solution. The calculations have been performed using both the Becke 3-parameter Lee-Yang-Parr functional and the recently developed Coulomb-attenuated method functional. Solvation has been investigated by examining the effects of the reaction field, non-equilibrium solvation, geometry relaxation, and cavity field. The inclusion of solvent effects leads to significantly better agreement with experimental observations.

  • 29.
    Gador, Niklas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Zhang, Bo
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Hansson, T
    Molecular rotation-vibration coupling by quantum wavepacket interference at potential energy curve crossings2005Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 412, nr 4-6, s. 386-390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum wavepacket interference is shown to result in modulation of the ultrafast transient anisotropy of a diatomic molecule. The molecule is in a state comprising two bound electronic states at intermediate coupling strength and the anisotropy modulation enters via variations in the instantaneous contributions of the initial states to the total anisotropy. A necessary condition for the appearance of the modulation is that the involved rotational states possess different vibrational dynamics. The wavepacket interference mediates this coupling by imposing dynamical restrictions on the accessible vibrational phase space which depend on the rotational state.

  • 30.
    Gel'mukhanov, Faris
    et al.
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Baev, A.
    Luo, Yi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Resonant X-ray Raman scattering from dense gases and solutions2001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 346, nr 06-maj, s. 437-442Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To complement conventional theory of resonant X-ray Raman scattering (RXS) adapted either for rarefied gases or solids, we propose a theory and corresponding analysis for RXS from dense gases and solutions. We show that the dephasing broadening of the spectral lines due to interaction with buffer or solvent particles qualitatively changes the physics of the X-ray scattering. The dephasing results in an additional, two-step (TS) scattering, contribution to the RXS cross-section, which interferes with the Raman one-step (OS) channel and which shows a nondispersive behaviour, This results in a doubling of the spectral lines by detuning the excitation frequency away from resonance. The theory is demonstrated numerically for RXS of formaldehyde in solution.

  • 31.
    Georgieva, Polina
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Himo, Fahmi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Density functional theory study of the reaction mechanism of the DNA repairing enzyme alkylguanine alkyltransferase2008Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 463, nr 1-3, s. 214-218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reaction mechanism of human O6-alkylguanine-DNA alkyltransferase (AGT) is studied using density functional theory. AGT repairs alkylated DNA by directly removing the alkyl group from the O6 position of the guanine. A quantum chemical model of the active site was devised based on the recent crystal structure of the AGT–DNA complex. The potential energy curve is calculated and the stationary points are characterized. It is concluded that the previously proposed reaction mechanism is energetically plausible. In this mechanism, His146 first acts as a water-mediated general base to activate Cys145, which then performs a nucleophilic attack to dealkylate the guanine base.

  • 32.
    Guimaraes, Freddy Fernandes
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Gelmukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Cesar, A.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Quantum wave packet revivals in IR plus X-ray pump-probe spectroscopy2005Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 405, nr 4-6, s. 398-403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The wave packet revivals constitute a central concept of X-ray spectroscopy with ultra-high spectral resolution. The revival phenomenon allows to resolve the anharmonical shift or rotational structure by means of time dependent measurements and makes X-ray pump-probe spectroscopy a powerful technique to study long-term dynamics of molecules in different phases. We study the revivals referring to the X-ray absorption spectrum of the NO molecule driven by strong infrared pulse. It is shown that the phase sensitive trajectories of the center of gravity of the wave packets and the X-ray spectra copy each other.

  • 33. Guo, J. D.
    et al.
    Luo, Yi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Himo, Fahmi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Density functional theory study of the canthaxanthin and other carotenoid radical cations2002Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 366, nr 02-jan, s. 73-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    B3LYP hybrid density functional theory method is employed to study the five carotenoid radical cations of canthaxanthin (1), 7',7'-dimethyl-7'-apo-beta-carotene (2), 8'-apo-beta-carotene-8'-al hydrazone (3), 7',7'-dicyano-7'-apo-beta-carotene (4), and 8'-apo-beta-carotene-8'-al (5). The radicals are characterized by means of their geometries, spin populations, and isotropic hyperfine coupling constants. It is shown that for all the systems, the unpaired spin is delocalized over the whole pi-conjugated system in an odd-alternant pattern. As a result of this, the hyperfine coupling constants are rather low. The radical cations of 1, 2, and 3, have very similar properties to the unsubstituted P-carotene radical, while the dicyano- and aldehyde-substitutions result in significantly different electronic structures.

  • 34. Himo, Fahmi
    Stability of protein-bound glycyl radical: a density functional theory study2000Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 328, nr 3, s. 270-276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory is used to study different models of the glycyl radical in proteins. The radical is characterized by means of the C-alpha-H bond strength, geometry, spin distribution, and hyperfine parameters. It is shown that, due to substituent effects from the peptide bond, the protein-bound glycyl radical is less stable than the nonprotein-bound one. This effect is of great importance for the biological function of the glycyl radical. The capto-dative resonance stabilization is confirmed, and new resonances are suggested to arise due to the peptide bond, resulting in further delocalization of the unpaired spin.

  • 35.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Photocatalyst AgInS2 for active overall water-splitting: A first-principles study2014Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 591, s. 189-192Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure of photocatalyst AgInS2 has been investigated by first-principles calculation. Our results demonstrate that the band edge positions of chalcopyrite and orthorhombic AgInS2 straddle the water redox potentials. From the band offset calculation, we find that Ga-doping of AgInS2 shifts the conduction band minimum upwards, whereas Cu-doping of AgInS2 shifts the valence band maximum upwards. By (Ag,Cu)(In,Ga)S-2 alloying one can thereby tailor both the band edge positions and the band gap energy, and this effect provides an approach to optimize the band properties for overall water splitting.

  • 36. Hugosson, Håkan Wilhelm
    et al.
    Jansson, U.
    Johansson, Börje
    Eriksson, O.
    Phase stability diagrams of transition metal carbides, a theoretical study2001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 333, nr 6, s. 444-450Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The experimental phase diagrams at T = 0 of the refractory compounds ZrC, NbC and MoC have been reproduced with great accuracy from first principles theory. The energy of formation for these compounds has been calculated for several phases and stoichiometries in order to understand, for example, the differences and changes in homogeneity ranges found in these systems. This determination of relative phase stabilities for a wide range of concentrations is necessary for first principles determination of phase diagrams for these compounds with complex bonding and structural properties as well as technological importance.

  • 37. Jansik, B.
    et al.
    Rizzo, A.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Response theory calculations of two-photon circular dichroism2005Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 414, nr 06-apr, s. 461-467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The feasibility of calculations of two-photon circular dichroism (TPA-CD) by means of response theory is demonstrated. The results from sample applications, involving the calculation of residues of appropriate frequency dependent quadratic response functions within a density functional theory model, show that the structural content of TPA-CD spectra is very different from both normal circular dichroism and two-photon absorption, indicating a unique fingerprinting functionality for chiral species. Combined with increased penetrability of the infrared exciting light and the confocal nature of two-photon absorption, this makes TPA-CD a useful tool for biomolecular identification.

  • 38.
    Jha, Prakash Chandra
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Jansson, Emil
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Triplet energies of pi-conjugated polymers2006Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 424, nr 03-jan, s. 23-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report time-dependent density functional theory calculations of singlet-triplet splittings (S-0-T-1) and triplet-triplet (T-1-T-n) excitation energies of a range of conjugated polymers with relevance as light emitting diode materials. The errors obtained from the computed results are discussed in terms of maximum and mean deviation values in comparison with experimental data. The theoretical methodology shows in general a sufficient agreement to warrant its use for prediction of polymer (S-0-T-1) and (T-0-T-1) excitation energies. We confirm that spin contamination of the triplet state is not a serious problem when computing triplet-triplet spectra of organic oligomers.

  • 39.
    Jiang, Jun
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lu, W.
    Natl. Lab. for Infrared Physics, Shanghai Inst. of Technical Physics, Chinese Academy of Sciences.
    Luo, Yi
    KTH, Tidigare Institutioner                               , Kemi.
    Length dependence of coherent electron transportation in metal-alkanedithiol-metal and metal-alkanemonothiol-metal junctions2004Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 400, nr 4-6, s. 336-340Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have applied the elastic-scattering Green's function theory to study the coherent electron transportation processes in both metal-alkanedithiol-metal (gold-[S(CH2)(n)S]-gold, n = 8-14) and metal-alkanemonothiol-metal (gold-[H(CH2)(n)S]-gold, n = 814) at the hybrid density functional theory level. It is shown that the current decreases exponentially with the molecular length. At the low temperature limit the electron decay rate, beta, for alkanedithiol junction is found to be around 0.30/CH2 at 1.0 V bias, much smaller than the calculated value of 0.60/CH2 for alkanemonothiol junction. The decay rate for alkanedithiol junction at the room temperature is neither sensitive to the activation of the Au-S stretching vibrational mode nor to the external bias. The calculated current-voltage characteristics and decay rates for both junctions are in excellent agreement with the corresponding experimental results.

  • 40. Johnson, Claes Magnus
    et al.
    Sugiharto, Albert B.
    Roke, Sylvie
    Surface and bulk structure of poly-(lactic acid) films studied by vibrational sum frequency generation spectroscopy2007Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 449, nr 03-jan, s. 191-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surface and bulk structure of various poly-(lactic acid) (PLA) films were examined by vibrational sum frequency generation (VSFG). In contrast to linear infrared spectroscopy, the VSFG spectra show significantly different characteristics in the CH stretching region. For crystalline PLLA we observed strong surface and bulk signals, which were caused by both the order and the symmetry of the space group. Amorphous PLLA and racemically composed PDLLA were found to consist of a relatively disordered bulk. Contrary to the bulk, all surfaces studied generated VSFG signal caused by the broken symmetry at the polymer/air interface.

  • 41. Jonsson, D.
    et al.
    Luo, Y.
    Ruud, K.
    Norman, P.
    Ågren, H.
    Calculations of circular intensity differences in electric-field-induced second harmonic generation1998Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 288, nr 2-4, s. 371-376Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio calculations of electric-field induced second-harmonic generation for chiral molecules are presented. The calculations employ cubic response theory and take into account electric-dipole, electric-quadrupole and magnetic-dipole interactions, which result in an intensity dependence on the helicity of the light. The circular intensity difference is calculated for the chiral molecules twisted ethylene, trans-1,2-dimethylcyclopropane and methyloxirane. The calculated circular intensity differences are small - being of the order of 10-4-10-3 - but such electric-field induced second harmonic generation intensity dependencies should be experimentally detectable.

  • 42. Jun, J.
    et al.
    Wei, L.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Electronic structures and transportation properties of sub-60 nm long single-walled carbon nanotubes2005Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 416, nr 06-apr, s. 272-276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has long been a challenge to calculate electronic structures and properties of molecular systems containing more than 10000 electrons using first-principles approaches. We have developed an elongation method that allows to treat 59 nm long single-walled carbon nanotubes (SWCNTs) containing 4770 carbon atoms at the hybrid density functional theory level. An unexpected oscillating behaviour of the energy gap with respect to the length of the nanotube is observed. The calculated current voltage characteristics of sub-20 nm SWCNTs are in excellent agreement with the experimental results, revealing the underlying mechanism of electron transport in nanosized SWCNTs for the first time.

  • 43.
    Kashtanov, Stepan
    et al.
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Rubio-Pons, Oscar
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Luo, Yi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Stäfstrom, Sven
    Linköpings Universitet.
    Csillag, Stefan
    Stockholms Universitet.
    Characterization of aza-fullerene C58N2 isomers by X-ray spectroscopy2003Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 371, nr 02-jan, s. 98-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray photoelectron and near-edge X-ray absorption fine-structure spectra (NEXAFS) of four isomers of C58N2 are predicted by means of density-functional theory calculations. A strong isomer dependence for both types of spectra are found. The spectroscopic findings are discussed in conjunction with results from electronic and geometric structure optimizations.

  • 44. Keal, T. W.
    et al.
    Helgaker, T.
    Salek, Pawel
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Tozer, D. J.
    Choice of exchange-correlation functional for computing NMR indirect spin-spin coupling constants2006Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 425, nr 1-3, s. 163-166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The choice of exchange-correlation functional for the determination of indirect nuclear spin-spin coupling constants in density-functional theory is considered. In an assessment of one-bond (1)J(CH) couplings, the PBE functional was recently shown [S.N. Maximoff, J.E. Peralta, V. Barone, G.E. Scuseria, J. Chem. Theory Comput. 1 (2005) 541] to perform well, significantly outperforming B3LYP. For couplings involving N, 0, and F atoms in simple molecules, we demonstrate that the opposite is observed; PBE is considerably less accurate than B3LYP. By contrast, the B97-2 and B97-3 semi-empirical functionals provide good, consistent quality couplings for all these atom types in an extensive assessment.

  • 45.
    Kvashnina, K. O.
    et al.
    Uppsala Universitet.
    Butorin, S. M.
    Uppsala Universitet.
    Modin, A.
    Uppsala Universitet.
    Soroka, Inna
    Uppsala Universitet.
    Marcellini, M.
    Uppsala Universitet.
    Nordgren, J.
    Uppsala Universitet.
    Guo, J. -H
    SKB, Sweden.
    Werme, L.
    Uppsala Universitet.
    In-situ x-ray absorption study of copper films in ground water solutions2007Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 447, nr 1-3, s. 54-57Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Damage to copper by corrosion can be decreased by modifying the chem. of the copper surface environment. The surface modification of oxidized copper films induced by chem. reaction with Cl- and HCO3- ions in aq. solns. was monitored by in-situ x-ray absorption spectroscopy. The corrosion of copper can be significantly decreased by adding even a small amt. of sodium bicarbonate. The copper films corroded rapidly in chloride solns. of synthetic ground water, whereas the same soln. contg. 1.1 mM HCO-3 prevented or slowed down the corrosion processes. [on SciFinder(R)]

  • 46.
    Li, Hongbao
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China, China.
    Lin, Zijing
    University of Science and Technology of China.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China, China.
    A Fragment Based Step-by-Step Strategy for Determining the Most Stable Conformers of Biomolecules2014Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 610, s. 303-309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For biomolecules of increased size and flexibility, more efficient and reliable strategiesare always needed to determine their stable low-energy conformers. Here, we propose a fragment basedstep-by-step strategy to search for the full conformational space of biomolecules. In this strategy, themolecule is divided into several fragments and each of them is systematically optimized in a step-bystepfashion. It can significantly reduce the computational cost without losing any accuracy asdemonstrated by the conformer search of several representative di-/tri-/tetra- peptides. Such an approachwill be very useful for finding the stable conformers of large biomolecules.

  • 47.
    Li, Hongbao
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Lin, Zijing
    University of Science and Technology of China,.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Gas-phase IR spectroscopy of deprotonated amino acids: Global or Local minima?2014Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 598, s. 86-90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory calculations for the structure and IR spectroscopy of deprotonated tyrosine and cysteine molecules in gas phase have been carried out to resolve the on-going debate about the global minimum of deprotonated amino acids. It is found that the global minimum of the deprotonated specie is not always directly produced from the most stable neutral conformer. Depending on the setup, the experimental IR spectroscopy of deprotonated amino acids could only give the information of the local minima of the deprotonated species.

  • 48.
    Li, Hongbao
    et al.
    KTH, Skolan för bioteknologi (BIO).
    Lin, Zijing
    University of Science and Technology of China.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China.
    The Role of Dimerization on the Structure Transformation of Arginine in Gas Phase2014Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 608, s. 398-403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The equilibrium distribution of arginine molecules in canonical and zwitterionicforms predicted by the theory failed to correctly reproduce the double-peak feature observedin the IR experiment. We have shown from first principles calculations that the energeticallyfavorable dimerization of zwitterions can effectively eliminate the pathway for the structureconversion between two distinct canonical forms and reduce the probability for thesecanonical forms to reach their thermal equilibrium. The role of dispersion effect is discussed.It suggests that the experimental IR spectrum is determined by the way how the conformersof arginine are initially generated.

  • 49.
    Li, JunFeng
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Xiamen University, China.
    Tian, GuanJun
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Cao, ZeXing
    Theoretical studies on the vibrationally-resolved absorption and fluorescence spectra of H-Pyrene(+) and H-Coronene(+)2015Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 641, s. 57-61Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    H-Pyrene and H-Coronene are important carrier candidates for the diffuse interstellar band. In order to understand the observed absorption and fluorescence emission spectra of H-Pyrene and H-Coronene, time-dependent density functional theory (TD-DFT) method and Franck-Condon approximation have been employed to simulate the corresponding vibrationally-resolved optical spectra. For H-Pyrene, the calculated absorption, emission and 0-0 band energies are in good agreement with the experimental values. The strong absorption and emission vibrational peaks near the 0-0 band match well with the experiment peaks. A noticeable deviation for several weak peaks far away from the origin band is observed, as a result of the vibronic coupling with other excited states. For H-Coronene, the predicted vibrationally resolved electronic absorption and emission spectra resemble very well their experimental counterparts spectra, allowing to fully assign the observed vibronic peaks.

  • 50.
    Li, Shen
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jia, Xiaopeng
    Ma, Hongan
    First-principles investigation of electronic structure and transport properties of CoSb3 under different pressures2012Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 549, s. 22-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure of pure CoSb3 (undoped) and the electronic transport properties as a function of chemical potential (mu) of CoSb3 under different pressures were studied systematically and in detailin our research. Direct band gap change to indirect band gap with increasing pressure was found for the undoped CoSb3. The electrical conductivity of undoped CoSb3 significantly decreases with increasing pressure from 0 to 10 GPa, the Seebeck coefficient of undoped CoSb3 significantly enhanced with increasing pressure. The n-type of doping in CoSb3 would be more favorable for enhancing the thermoelectric properties than that of p-type doping under pressure.

123 1 - 50 av 116
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf