Ändra sökning
Avgränsa sökresultatet
1234567 151 - 200 av 778
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • 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.
  • 151.
    Duan, Sai
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Xu, Xin
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tian, Zhong-Qun
    Molecular polarization bridging physical and chemical enhancements in surface enhanced Raman scattering2011Ingår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 47, nr 41, s. 11438-11440Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a practical method which demonstrates how the physical and chemical enhancements in SERS for a molecule adsorbed on metal junctions are conceptually coupled through the polarization of the molecule and its surroundings. Calculations with the state-of-the-art density functional reveal that the coupling factor considered in the present work can be as large as 10(6), such that it is indeed important for certain vibrational modes.

  • 152.
    Duan, Sai
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Xu, Xin
    Tian, Zhong-Qun
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    A Hybrid Molecular Dynamics and First Principles Study on the Workfunction of a Pt(1 1 1) Electrode Immersed in Aqueous Solution at Room TemperatureArtikel i tidskrift (Övrigt vetenskapligt)
  • 153.
    Duan, Sai
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Xu, Xin
    Tian, Zhong-Qun
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Hybrid molecular dynamics and first-principles study on the work function of a Pt(111) electrode immersed in aqueous solution at room temperature2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 4, s. 045450-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With a combined molecular dynamics simulation and first-principles calculations, we have investigated a metal surface immersed in aqueous solution at room temperature using a Pt(111) electrode as an example. With the inclusion of thermal average effects at room temperature, the calculated averaged work function is found to be in good agreement with the experimental measurements. The electron redistribution at the interface of the topmost Pt(111) slab layer and the first water layer plays an important role in controlling the work function. A broad distribution of calculated work functions caused by the thermal motions of the dipolar solvents is obtained from statistical sampling, which implies that the chemical reactivity of a metal electrode in aqueous solution is a dynamic property at least in the nanoscale. Such a microscopic understanding helps to understand the behavior of complex electrochemical double layers.

  • 154.
    Duan, Sai
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Xu, Xin
    Tian, Zhong-Qun
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Thermal Eects on Electronic Properties of CO/Pt(111) in WaterArtikel i tidskrift (Övrigt vetenskapligt)
  • 155. Ekström, Ulf
    et al.
    Norman, Patrick
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. KTH.
    Carravetta, Vincenzo
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Polarization propagator for X-ray spectra2006Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, nr 14Artikel i tidskrift (Refereegranskat)
    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.

  • 156. Eriksen, Janus J.
    et al.
    Olsen, Jogvan Magnus H.
    Aidas, Kestutis
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Mikkelsen, Kurt V.
    Kongsted, Jacob
    Computational Protocols for Prediction of Solute NMR Relative Chemical Shifts. A Case Study of L-Tryptophan in Aqueous Solution2011Ingår i: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 32, nr 13, s. 2853-2864Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, we have applied two different spanning protocols for obtaining the molecular conformations of L-tryptophan in aqueous solution, namely a molecular dynamics simulation and a molecular mechanics conformational search with subsequent geometry re-optimization of the stable conformers using a quantum mechanically based method. These spanning protocols represent standard ways of obtaining a set of conformations on which NMR calculations may be performed. The results stemming from the solute-solvent configurations extracted from the MD simulation at 300 K are found to be inferior to the results stemming from the conformations extracted from the MM conformational search in terms of replicating an experimental reference as well as in achieving the correct sequence of the NMR relative chemical shifts of L-tryptophan in aqueous solution. We find this to be due to missing conformations visited during the molecular dynamics run as well as inaccuracies in geometrical parameters generated from the classical molecular dynamics simulations.

  • 157.
    Erro, Samuel Martinez
    et al.
    Stockholm Univ, Dept Organ Chem, Stockholm, Sweden..
    Sanz-Marco, Amparo
    Stockholm Univ, Dept Organ Chem, Stockholm, Sweden..
    Gomez, Antonio Bermejo
    Stockholm Univ, Dept Organ Chem, Stockholm, Sweden..
    Vazquez-Romero, Ana
    Stockholm Univ, Dept Organ Chem, Stockholm, Sweden..
    Ahlquist, Mårten
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Martin-Matute, Belen
    Stockholm Univ, Dept Organ Chem, Stockholm, Sweden..
    Metal-free stereospecific isomerization of electron-deficient allylic alcohols and allylic ethers2017Ingår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Artikel i tidskrift (Övrigt vetenskapligt)
  • 158. Ertan, Emelie
    et al.
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Siberian Fed Univ, Russia.
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Siberian Fed Univ, Russia.
    Hennies, Franz
    Rubensson, Jan-Erik
    Schmitt, Thorsten
    Strocov, Vladimir N.
    Zhou, Kejin
    Iannuzzi, Marcella
    Foehlisch, Alexander
    Odelius, Michael
    Pietzsch, Annette
    Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 14, artikel-id 144301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.

  • 159.
    Fahleson, Tobias
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Norman, Patrick
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Resonant-convergent second-order nonlinear response functions at the levels of Hartree-Fock and Kohn-Sham density functional theory2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, nr 14, artikel-id 144109Artikel i tidskrift (Refereegranskat)
    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.

  • 160. Fahleson, Tobias
    et al.
    Olsen, Jógvan Magnus Haugaard
    Norman, Patrick
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Rizzo, Antonio
    A QM/MM and QM/QM/MM study of Kerr, Cotton--Mouton and Jones linear birefringences in liquid acetonitrile2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    QM/MM and QM/QM/MM protocols are applied to the ab initio study of the three linear bire-fringences Kerr, Cotton–Mouton, and Jones, as shown by acetonitrile in the gas and pureliquid phases. The relevant first-order properties as well as linear, quadratic, and cubicfrequency-dependent response functions were computed using time-dependent Kohn–Shamdensity-functional theory with use of the standard CAM-B3LYP functional. In the liquid phase,a series of room temperature (293.15 K) molecular dynamics snapshots were selected, for whichaveraged values of the observables were obtained at an optical wavelength of 632.8 nm. Thebirefringences were computed for electric and magnetic induction fields corresponding to the lab-oratory setup previously employed by Roth and Rikken in Phys. Rev. Lett. 85, 4478, (2000).Under these conditions, acetonitrile is shown to exhibit a weak Jones response — in fact roughly6.5 times smaller than the limit of detection of the apparatus employed in the measurementsmentioned above. A comparison is made with the corresponding gas-phase results and an as-sessment is made of the index of measureability, estimating the degree of overlap of the threebirefringences in actual measurements. For acetonitrile, it is shown that this index is a factorof 3.6 and 6.7 larger than that of methylcyclopentadienyl-Mn-tricarbonyl and cyclohexadienyl-Fe-tricarbonyl, respectively — two compounds reported in Phys. Rev. Lett. 85, 4478, (2000) to exhibita strong Jones signal.

  • 161. Fahleson, Tobias
    et al.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Norman, Patrick
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Linköping University, Sweden.
    A Polarization Propagator for Nonlinear X-ray Spectroscopies2016Ingår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, nr 11, s. 1991-1995Artikel i tidskrift (Refereegranskat)
    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.

  • 162.
    Fan, Ting
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Duan, Lele
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Huang, Ping
    Chen, Hong
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Daniel, Quentin
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Ahlquist, Mårten S. G.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.2017Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, nr 4, s. 2956-2966Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many Ru water oxidation catalysts have been documented in the literature. However, only a few can catalyze the O-O bond formation via the radical coupling pathway, while most go through the water nucleophilic attack pathway. Understanding the electronic effect on the reaction pathway is of importance in design of active water oxidation catalysts. The Ru-bda (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalyst is one example that catalyzes the 0-0 bond formation via the radical coupling pathway. Herein, we manipulate the equatorial backbone ligand, change the doubly charged bda(2-) ligand to a singly charged tpc- (2,2':6',2 ''-terpyridine-6-carboxylate) ligand, and study the structure activity relationship. Surprisingly, kinetics measurements revealed that the resulting Ru-tpc catalyst catalyzes water oxidation via the water nucleophilic attack pathway, which is different from the Ru-bda catalyst. The O-O bond formation Gibbs free energy of activation (AGO) at T = 298.15 K was 20.2 +/- 1.7 kcal mol(-1). The electronic structures of a series of Ru-v=O species were studied by density function theory calculations, revealing that the spin density of O-Ru=O of Ru-v=O is largely dependent on the surrounding ligands. Seven coordination configuration significantly enhances the radical character of Ru-v=O.

  • 163.
    Fan, Ting
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Zhan, Shaoqi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ahlquist, Mårten S. G.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Why Is There a Barrier in the Coupling of Two Radicals in the Water Oxidation Reaction?2016Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, nr 12, s. 8308-8312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two radicals can form a bond without an energetic barrier. However, the radical coupling mechanism in ruthenium catalyzed water oxidation has been found to be associated with substantial activation energies. Here we have investigated the coupling reaction of [Ru=O(bda)L-2](+) catalysts with different axial L ligands. The interaction between the two oxo radical moieties at the Ru(V) state was found to have a favorable interaction in the transition state in comparison to the prereactive complex. To further understand the existence of the activation energy, the activation energy has been decomposed into distortion energy and interaction energy. No correlation between the experimental rates and the calculated coupling barriers of different axial L was found, showing that more aspects such as solvation, supramolecular properties, and solvent dynamics likely play important roles in the equilibrium between the free Ru-v=0 monomer and the [Ru-v=O center dot center dot center dot O=Ru-v] dimer. On the basis of our findings, we give general guidelines for the design of catalysts that operate by the radical coupling mechanism.

  • 164.
    Fang, Qiu
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Mechanistic photodissociation of small molecules explored by electronic structure calculation and dynamics simulation2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 165.
    Fang, Qiu
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Synchronous Concerted Four-Body Photodissociation of Oxalyl Chloride Explored by ab initio based Molecular Dynamics SimulationsManuskript (preprint) (Övrigt vetenskapligt)
  • 166.
    Farahani, Pooria
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Theoretical Studies of Solvent Effect on Normal Mode Analysis and Thermodynamic Properties of Zigzag (5, 0) Carbon Nanotube2011Ingår i: Fullerenes, nanotubes, and carbon nanostructures (Print), ISSN 1536-383X, E-ISSN 1536-4046, Vol. 19, s. 469-482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Normal mode analysis is an important tool for studying the structure and dynamicsof nanosized systems. The vibrational frequencies obtained can be used to relateobserved spectra to the details of the molecular structure, dynamics and other thermodynamicproperties. It is important to understand the energetic, stability-dependentphysical properties of zigzag (5, 0) carbon nanotube. In this study we have employedsemi-empirical, DFT, molecular mechanic methods. Our results show that the processof introducing (5, 0) carbon nanotube to different dielectrics is energetically comparablein maximum energy; with increasing the dielectric, the energy declines and thestability increases. AM1and PM3 have the same results in the semi-empirical methodand have good agreement relative to each other.

  • 167.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Baader, Wilhelm J.
    Unimolecular Decomposition Mechanism of 1,2-Dioxetanedione: Concerted or Biradical? That is the Question!2017Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 121, s. 1189-1194Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Determination of the ground- and excited-stateunimolecular decomposition mechanisms of 1,2-dioxetanedionegives a level of insight into bimolecular decomposition reactionsof this kind for which some experimental results are reported.Although a few studies have put some effort to describe abiradical mechanism of this decomposition, there is still no systematic study that proves an existence of a biradical character.In the present study, state-of-the-art high-level multistatemulticonfigurational reference second-order perturbation theorycalculations are performed to describe the reaction mechanismof 1,2-dioxetanedione in detail. The calculations indicate that thedecomposition of this four-membered ring peroxide containingtwo carbonyl carbon atoms occurs in concerted but notsimultaneous fashion, so-called “merged”, contrary to the caseof unimolecular 1,2-dioxetane and 1,2-dioxetanone decompositions where biradical reaction pathways have been calculated. Atthe TS of the ground-state surface, the system enters an entropic trapping region, where four singlet and four triplet manifoldsare degenerated, which can lead to the formation of triplet and singlet excited biradical species. However, these excited specieshave to overcome a second activation barrier for C−C bond cleavage for excited product formation, whereas the ground-stateenergy surface possesses only one TS. Thus our calculations indicate that the unimolecular decomposition of 1,2-dioxetanedioneshould not lead to efficient excited-state formation, in agreement with the lack of direct emission from the peroxyoxalate reaction.

  • 168.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Oliveira, Marcelo
    Fdez. Galvan, Ignacio
    Baader, Wilhelm J.
    A combined theoretical and experimental study onthe mechanism of spiro-adamantyl-1,2-dioxetanone decomposition2017Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, s. 17462-17472Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1,2-Dioxetanones have been considered as model compounds for bioluminescence processes. Theunimolecular decomposition of these prototypes leads mainly to the formation of triplet excited stateswhereas in the catalysed decomposition of these peroxides singlet states are formed preferentially.Notwithstanding, these cyclic peroxides are important models to understand the general principles ofchemiexcitation as they can be synthesised, purified and characterised. We report here results ofexperimental and theoretical approaches to investigating the decomposition mechanism of spiroadamantyl-1,2-dioxetanone. The activation parameters in the unimolecular decomposition of thisderivative have been determined by isothermal kinetic measurements (30–70 C) and thechemiluminescence activation energy calculated from the correlation of emission intensities. Theactivation energy for peroxide decomposition proved to be considerably lower than thechemiluminescence activation energy indicating the existence of different reaction pathways for groundand excited state formation. These experimental results are compared with the calculations at thecomplete active space second-order perturbation theory (CASPT2), which reveal a two-step biradicalmechanism starting by weak peroxide bond breakage followed by carbon–carbon elongation. Thetheoretical findings also indicate different transition state energies on the excited and ground statesurfaces during the C–C bond cleavage in agreement with the experimental activation parameters.

  • 169.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Roca-Sanjuan, Daniel
    Aquilante, Francesco
    A Two-Scale Approach to Electron Correlationin Multiconfigurational Perturbation Theory2014Ingår i: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 35, s. 1609-1617Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new approach for the calculation of dynamicelectron correlation effects in large molecular systems usingmulticonfigurational second-order perturbation theory(CASPT2). The method is restricted to cases where partitioningof the molecular system into an active site and an environmentis meaningful. Only dynamic correlation effects derivedfrom orbitals extending over the active site are included at theCASPT2 level of theory, whereas the correlation effects of theenvironment are retrieved at lower computational costs. Forsufficiently large systems, the small errors introduced by thisapproximation are contrasted by the substantial savings inboth storage and computational demands compared to thefull CASPT2 calculation. Provided that static correlation effectsare correctly taken into account for the whole system, the proposedscheme represent a hierarchical approach to the electroncorrelation problem, where two molecular scales aretreated each by means of the most suitable level of theory.

  • 170.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Roca-Sanjuan, Daniel
    Frances-Monerris, Antonio
    Fdez. Galvan, Ignacio
    Lindh, Roland
    Liu, Ya-Jun
    Advances in computationalphotochemistry and chemiluminescenceof biological and nanotechnologicalmolecules2017Ingår i: Photochemistry / [ed] Elisa Fasani and Angelo Albini, Royal Society of Chemistry, 2017, 44, s. 16-60Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Recent advances (2014–2015) in computational photochemistry and chemiluminescencederive from the development of theory and from the application of state-of-the-art andnew methodology to challenging electronic-structure problems. Method developmentshave mainly focused, first, on the improvement of approximate and cheap methods toprovide a better description of non-adiabatic processes, second, on the modification ofaccurate methods in order to decrease the computation time and, finally, on dynamicsapproaches able to provide information that can be directly compared with experimentaldata, such as yields and lifetimes. Applications of the ab initio quantum-chemistry methodshave given rise to relevant findings in distinct fields of the excited-state chemistry.We brieflysummarise, in this chapter, the achievements on photochemical mechanisms andchemically-induced excited-state phenomena of interest in biology and nanotechnology.

  • 171.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Roca-Sanjuan, Daniel
    Zapata, Felipe
    Lindh, Roland
    Revisiting the Nonadiabatic Process in 1,2-Dioxetane2013Ingår i: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 9, s. 5404-5411Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Determining the ground and excited-statedecomposition mechanisms of 1,2-dioxetane is essential tounderstand the chemiluminescence and bioluminescencephenomena. Several experimental and theoretical studies hasbeen performed in the past without reaching a converged description. The reason is in part associated with the complex nonadiabatic process taking place along the reaction. The present study is an extension of a previous work (De Vico, L.;Liu, Y.-J.; Krogh, J. W.; Lindh, R. J. Phys. Chem. A 2007, 111,8013−8019) in which a two-step mechanism was established for the chemiluminescence involving asynchronous O−O′ andC−C′ bond dissociations. New high-level multistate multiconfigurational reference second-order perturbation theory calculations and ab initio molecular dynamics simulations at constant temperature are performed in the present study, which provide further details on the mechanisms and allow to rationalize further experimental observations. In particular, the new results explain the high ratio of triplet to singlet dissociation products.

  • 172.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Vacher, Morgane
    Valentini, Alssio
    Frutos, Luis M.
    Fdez. Galvan, Ignacio
    Karlsson, Hans
    Lindh, Roland
    How Do Methyl Groups Enhance the Triplet Chemiexcitation Yield ofDioxetane?2017Ingår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, s. 3790-3794Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chemiluminescence is the emission of light as aresult of a nonadiabatic chemical reaction. The present work isconcerned with understanding the yield of chemiluminescence,in particular how it dramatically increases upon methylation of1,2-dioxetane. Both ground-state and nonadiabatic dynamics(including singlet excited states) of the decomposition reactionof various methyl-substituted dioxetanes have been simulated.Methyl-substitution leads to a significant increase in thedissociation time scale. The rotation around the O−C−C−Odihedral angle is slowed; thus, the molecular system stayslonger in the “entropic trap” region. A simple kinetic model isproposed to explain how this leads to a higher chemiluminescence yield. These results have important implications for the designof efficient chemiluminescent systems in medical, environmental, and industrial applications.

  • 173.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Yagoobi Nia, Narges
    Sabzyan, Hassan
    Zendehdel, Mahmoud
    Oftadeh, Mohsen
    A combined computational and experimental study of the [Co(bpy)3]2+/3+ complexesas one-electron outer-sphere redox couplesin dye-sensitized solar cell electrolyte media2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, s. 11481-11491Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A combined experimental and computational investigation conducted to understand the nature of theinteractions between cobalt II/III redox mediators ([Co(bpy)3]2+/3+) and their impact on the performanceof the corresponding dye-sensitized solar cells (DSCs) is reported. The fully optimized equilibriumstructures of cobalt(II/III)-tris-bipyridine complexes in the gas phase and acetonitrile solvent are obtainedby the density functional B3LYP method using LanL2DZ and 6-31G(d,p) basis sets. The harmonicvibrational frequencies, infrared intensities and Raman scattering activities of the complexes are alsocalculated. The scaled computational vibrational wavenumbers show very good agreement with theexperimental values. Calculations of the electronic properties of the complexes are also performed atthe TD-B3LYP/6-31G(p,d)[LanL2DZ] level of theory. Detailed interpretations of the infrared and Ramanspectra of the complexes in different phases are reported. Detailed atomic orbital coefficients of thefrontier molecular orbitals and their major contributions to electronic excitations of the complexes arealso reported. These results are in good agreement with the experimental electrochemical values.Marcus diagram is derived for the electron transfer reaction Co(II) + D35+ - Co(III) + D35 using theCo–N bond length as a reaction coordinate.

  • 174.
    Farahani, Pooria
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Zendehdel, Mahmoud
    Yaghoobi Nia, Narges
    Nasr-Esfahani, Mojtaba
    Karbaschi, Mohamad Reza
    A combined computational and experimental study on the hydrogen bonding with chloride ion in a crab-claw like site of a new chromium Schiff base complex2016Ingår i: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 44, s. 150-161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A combined experimental and computational study to understand the nature of the hydrogen bonding ina crab-claw site of a new synthesized chromium Schiff base complex is reported. The fully optimizedequilibrium structures of the Cr(III) complex in the presence and absence of chloride ion are obtainedat the B3LYP functional in conjunction with LanL2DZ basis set. The crystal structure of the chromiumSchiff base complex consists of [CrL2]+ cation, in which L is a tridentate Schiff base ligand with full nameof N-(2-(2-hydroxyethylamino)ethyl)5-methoxysalicylideneimine, and a chloride anion, in the asymmetricunit. The chromium(III) cation possesses a distorted octahedral geometry, coordinated with four nitrogenand two phenoxo oxygen atoms derived from two chelate Schiff base ligands. The harmonicvibrational frequencies, infrared intensities and Raman scattering activities of the complexes are alsoreported. The scaled computational geometry and vibrational wavenumbers are in very good agreementwith the experimental values of single crystal X-ray diffraction and FT-IR, respectively. The electronicproperties calculations of the complexes are also performed at the TD-B3LYP/LanL2DZ level of theory.The spectroscopic excitation parameters obtained for frontier molecular orbitals of the complexes arereported as well. These findings are in good agreement with the experimental UV–Vis diffuse-reflectancespectroscopy. Parabolic diagrams are derived for the chloride insertion and hydrogen bonding in thecrab-claw site with the average optimized H H distances of the effective hydrogen atoms in the crabclawsite as reaction coordinate.

  • 175. Fransson, Thomas
    et al.
    Rehn, Dirk Robert
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Dreuw, Andreas
    Norman, P.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Static polarizabilities and C-6 dispersion coefficients using the algebraic-diagrammatic construction scheme for the complex polarization propagator2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 9, artikel-id 094301Artikel i tidskrift (Refereegranskat)
    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.

  • 176.
    Frecus, Bogdan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Theoretical studies of EPR parameters of spin-labels incomplex environments2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis encloses quantum chemical calculations performed in the framework of density functional response theory for evaluating electron paramagnetic resonance (EPR) spin Hamiltonian parameters of various spin-labels in different environments. These parameters are the well known electronic g-tensor and the nitrogen hyperfine coupling constants, which are extensively explored in this work for various systems. A special attention was devoted to the relationships that form between the structural and spectroscopic properties that can be accounted for as an environmental inuence. Such environmental effects were addressed either within a fully quantum mechanical formalism, involving simplified model structures that still capture the physical properties of the extended system, or by employing a quantum mechanics/molecular mechanics (QM/MM) approach. The latter implies that the nitroxide spin label is treated quantum mechanically, while the environment is treated in a classical discrete manner, with appropriate force fields employed for its description. The state-of- the art techniques employed in this work allow for an optimum accounting of the environmental effects that play an important role for the behaviour of EPR properties of nitroxides spin labels. One achievement presented in this thesis includes the first theoretical con_rmation of an empirical assumption that is usually made for inter-molecular distance measurement experiments in deoxyribonucleic acid (DNA), involving pulsed electron-electron double resonance (PELDOR) and site-directed spin labeling (SDSL) techniques. This refers to the fact that the EPR parameters of the spin-labels are not affected by their interaction with the nucleobases from which DNA is constituted. Another important result presented deals with the inuence of a supramolecular complex on the EPR properties of an encapsulated nitroxide spin-label. The enclusion complex affects the hydrogen bonding topology that forms around the R2NO moiety of the nitroxide. This, on the other hand has a major impact on its structure which further on governs the magnitude of the spectroscopic properties. The projects and results presented in this thesis offer an example of successful usage of modern quantum chemistry techniques for the investigation of EPR parameters of spin-labels in complex systems.

     

  • 177.
    Frecus, Bogdan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Oprea, Corneliu I.
    Panait, Petre
    Ferbinteanu, Marilena
    Cimpoesu, Fanica
    Girtu, Mihai A.
    Ab initio study of exchange coupling for the consistent understanding of the magnetic ordering at room temperature in V[TCNE] (x)2014Ingår i: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, nr 5, s. 1470-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report quantum chemical calculations providing the exchange coupling constants of the V[TCNE](2) model system, describing the amorphous room temperature molecular magnet V[TCNE] (x) (TCNE = tetracyanoethylene, x similar to 2). The geometry is optimized for the ideal lattice using density functional theory (DFT) calculations with periodic boundary conditions. Broken-symmetry DFT calculations indicate antiparallel spin alignment resulting in ferrimagnetic ordering, but heavily overestimate the value of the exchange coupling. Better estimates of the exchange coupling parameters between the V(II) ion and the [TCNE](-) anionic radical are obtained by means of multiconfigurational calculations performed on smaller molecular models cut from the optimized crystal lattice. Complete active space self-consistent field and multireference second-order perturbation theory calculations provide the sign and the strength of the nearest-neighbor as well as next-nearest-neighbor interactions along all three crystallographic directions. We are able to explain also intuitively the mechanism for antiferromagnetic spin coupling in terms of the superexchange pathways, discussing the role of the main four types of contributions to superexchange. Moreover, we clarify the influence of the transition metal ion on the strength of the exchange interaction and on the critical temperature for long-range ferrimagnetic ordering.

  • 178.
    Frecus, Bogdan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Natarajan Arul, Murugan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Vahtras, Olav
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Kongsted, Jacob
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    EPR spin Hamiltonian parameters of encapsulated spin-labels: impact of the hydrogen bonding topology2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 7, s. 2427-2434Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Encapsulation of spin-labels into "host'' compounds, like cucurbit[n]urils or cyclodextrins, in solutions has profound effects on the EPR spin Hamiltonian parameters of the spin-labels. In this work we study the microscopic origin of the EPR spin Hamiltonian parameters of spin-labels enclosed in hydrophobic cavities. We focus on the dependence of the EPR properties of encapsulated spin-labels on the hydrogen bonding topologies that occur upon encapsulation, and quantize various contributions to these parameters according to specific hydrogen bonding patterns. The obtained results provide refined insight into the role of the hydrogen bonding induced encapsulation shifts of EPR spin Hamiltonian parameters in solvated "spin-label@host compound'' complexes.

  • 179.
    Frecus, Bogdan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    π –stacking effects on the EPR parameters of a prototypical DNA spin label2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 25, s. 10466-10471Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The character and value of spin labels for probing environments like double-stranded DNA depends on the degree of changeof the spin Hamiltonian parameters of the spin label induced by the environment. Herein we provide a systematic theoreticalinvestigation of this issue, based on a density functional theory method applied to a spin labeled DNA model system, focusingon the dependence of the EPR properties of the spin label on the π stacking and hydrogen bonding that occur upon incorporatingthe spin label into selected base pair inside DNA. It is found that the EPR spin Hamiltonian parameters of the spin label is onlynegligibly affected by its incorporation into DNA, when compared to the its free form. This result gives theoretical ground forthe common empirical assumption regarding the behaviour of spin Hamiltonian parameters made in EPR based measurementsof distance between spin labels incorporated into DNA.

  • 180. Friese, D. H.
    et al.
    Bast, Radovan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Ruud, K.
    Five-photon absorption and selective enhancement of multiphoton absorption processes2015Ingår i: ACS Photonics, E-ISSN 2330-4022, Vol. 2, nr 5, s. 572-577Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study one-, two-, three-, four-, and five-photon absorption of three centrosymmetric molecules using density functional theory. These calculations are the first ab initio calculations of five-photon absorption. Even- and odd-order absorption processes show different trends in the absorption cross sections. The behavior of all even- and odd-photon absorption properties shows a semiquantitative similarity, which can be explained using few-state models. This analysis shows that odd-photon absorption processes are largely determined by the one-photon absorption strength, whereas all even-photon absorption strengths are largely dominated by the two-photon absorption strength, in both cases modulated by powers of the polarizability of the final excited state. We demonstrate how to selectively enhance a specific multiphoton absorption process.

  • 181. Fronzoni, Giovanna
    et al.
    Baseggio, Oscar
    Stener, Mauro
    Hua, Weijie
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tian, Guangjun
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China.
    Apicella, Barbara
    Alfe, Michela
    de Simone, Monica
    Kivimäki, Antti
    Coreno, Marcello
    Vibrationally resolved high-resolution NEXAFS and XPS spectra of phenanthrene and coronene2014Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, nr 4, s. 044313-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed a combined experimental and theoretical study of the C1s Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy and X-ray Photoelectron Spectroscopy in the gas phase of two polycyclic aromatic hydrocarbons (phenanthrene and coronene), typically formed in combustion reactions. In the NEXAFS of both molecules, a double-peak structure appears in the C1s -> LUMO region, which differ by less than 1 eV in transition energies. The vibronic coupling is found to play an important role in such systems. It leads to weakening of the lower-energy peak and strengthening of the higher-energy one because the 0 - n (n > 0) vibrational progressions of the lower-energy peak appear in nearly the same region of the higher-energy peak. Vibrationally resolved theoretical spectra computed within the Frank-Condon (FC) approximation and linear coupling model agree well with the high-resolution experimental results. We find that FC-active normal modes all correspond to in-plane vibrations.

  • 182.
    Fu, Qiang
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Understanding the Structure and Reaction of Single Molecules on Metal surfaces from First Principles2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The study of surface adsorption and reaction is not only interesting from a scientific point of view, but also important in many application fields such as energy, environment, catalysis, corrosion, electronic device, and sensor. Theoretical calculations are essential in these studies.

    In this thesis, first principles studies for the structure and reaction of some important single molecules on the surface are presented. Dehydrogenation of single trans-2-butene molecule on a Pd(110) surface is the first example. The adsorption configurations of both reactant and produce are assigned and the whole dehydrogenation pathway is revealed. Our calculations show that the reactant, i.e. trans-2-butene molecule, undergoes a rotation before dehydrogenation occurs, which is an important detail that cannot be observed directly in scanning tunneling microscopy (STM) experiments. The dissociation and rotation processes of single oxygen molecule on a Pt(111) surface have been a subject of extensive studies in the past. A new intermediate state with a peculiar configuration is identified. The puzzled adsorption site is well explained. The calculated energy barriers agree well with experimental results for both dissociation and rotation processes.

    Another aspect addressed in this thesis is the mechanism of molecular electronic switches induced by molecular structural changes. By carefully examining the tautomerization process of a naphthalocyanine molecule, an intermediate state is located on the potential surface of the tautomerization. Our calculations indicate that the experimentally observed switching involves four-states, rather than the two-state as proposed by the experimentalists. In a joint experimental and theoretical study the dehydrogenation, tautomerization, and mechanical switching processes of a single melamine molecule on a Cu(100) surface have been comprehensively examined. A new dual-functional molecular device with integrated rectifying and switching functions is made for the first time. In collaborating with another experimental group, we have simulated the switching process of a single 1,1,2,3,4,5-hexaphenylsilole molecule on a Cu(111) surface. The role of the orientation of the molecule is carefully examined and a new switching mechanism is proposed.

    Switching processes are strongly associated with the inelastic electron tunneling. We have proposed a statistical model that allows explaining the non-integer exponent in the power-law relationship between the switching rate and tunneling current. In this model, the importance of the randomness in inelastic electron excitations and the lifetime of the immediate state are emphasized. It has shown that the inelastic electron tunneling is a collection of various n-electron processes with different statistical weight.

  • 183.
    Fu, Qiang
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Cao, Xinrui
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Identification of the Scaling Relations for Binary Noble-Metal Nanoparticles2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 6, s. 2849-2854Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There exist a great many varieties of nanoparticles whose catalytic activities can be widely adjusted by changing their composition, shape, and size. Norskov's concepts to correlate the d-band center, adsorption energy, and activation energy offer an innovative approach to efficiently investigate the catalytic properties. Taking binary noble-metal polyhedral nanoparticles as representative systems, we found from first-principles simulations that the well-established scaling relations of the adsorption energies for extended surfaces can be seamlessly extended to the nanoscale. A systematic investigation of the correlation relations of the adsorption energies between the AH(x) groups and the corresponding A atoms in the binary noble-metal polyhedral nanoclusters of different compositions, shapes, and sizes clearly demonstrates the linear scaling relation. More remarkably, the scaling relation at the nanoscale can be effectively unified with the well-established scaling relations for extended surfaces. Such a description should be extremely helpful for the efficient screening of nanoparticles with superior catalytic properties.

  • 184.
    Fu, Qiang
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Active sites of Pd-doped flat and stepped Cu(111) surfaces for H 2 dissociation in heterogeneous catalytic hydrogenation2013Ingår i: ACS Catalysis, ISSN 2155-5435, Vol. 3, nr 6, s. 1245-1252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been shown in recent experiments that the Cu(111) surface doped by a small amount of Pd atoms can exhibit excellent catalytic performance toward the dissociation of H2 molecules. Here we performed systematic first-principles calculations to investigate the corresponding mechanism. Our results clearly demonstrate that a very small number of Pd atoms in the subsurface layer can effectively reduce the energy barrier of H2 dissociation, making the ensembles composed of the surface and contiguous subsurface Pd atoms as the active sites. The catalytic activity can be further improved if the Pd atoms are doped in the stepped Cu surfaces. The impact of the subsurface Pd atoms comes from an enhanced surface-adsorbate interaction caused by adjusting the electronic structure of the substrate. The important role played by the subsurface atoms offers an efficient approach to finely tune the surface activity by a very limited number of atoms. Our findings should be very useful for understanding and improving the catalytic properties of alloy systems for the industrially important hydrogenation reactions.

  • 185.
    Fu, Qiang
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Catalytic Activity of Single Transition-Metal Atom Doped in Cu(111) Surface for Heterogeneous Hydrogenation2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 28, s. 14618-14624Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single-atom alloy (SAA) has been considered as an effective strategy to achieve excellent catalytic performance toward heterogeneous hydrogenation. We have performed first-principles calculations for SAAs of Cu(111) with nine different transition-metal (TM) elements of the group VIIIB (TM = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt). The thermodynamic stability and the catalytic activity of these SAAs have been systematically investigated. It has been found that the SAA of Cu(111) surface doped by a single Ni, Rh, Pd, or Pt atom can stably exist. There are only three SAAs alloyed with Ni, Pd, and Pt that exhibit a lower energy barrier of H-atom diffusion with respect to that of H-2 dissociation, facilitating the spillover of H atoms. Ab initio molecular dynamics simulations have confirmed the results obtained from the energetic calculations. It is interesting to see that Ni and Pt are more suitable than the Pd as the alloying element of Cu, owing to the lower activation energies of H-2 dissociation. Our results will be important for improving the catalytic performance of SAAs for the industrially important hydrogenation reactions.

  • 186.
    Fu, Ying
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik (Stängd 20120101), Fotonik (Stängd 20120101).
    Optical properties of nanostructures2011Bok (Övrigt vetenskapligt)
    Abstract [en]

    Nanotechnology has been named as one of the most important areas of forthcoming technology because it promises to form the basis of future generations of electronic and optoelectronic devices. From the point of view of technical physics, all these developments greatly reduce the geometric sizes of devices, and thus the number of active electrons in the system. Quantum mechanical considerations about electronic states, electron transports, and various scattering processes, including light-matter interaction, are thus crucial. However, the theoretical study is extremely difficult. The authors' first numerical simulation work about a three-dimensional energy band structure calculation in 1995 took more than 6 months to complete for one bias configuration of a nanoscale metal-oxide-semiconductor field-effect transistor. With today's computation workstations the CPU time is reduced to less than 24 hours. This book discusses electrons and photons in and through nanostructures by the first-principles quantum mechanical theories and fundamental concepts (a unified coverage of nanostructured electronic and optical components) behind nanoelectronics and optoelectronics, the material basis, physical phenomena, device physics, as well as designs and applications. The combination of viewpoints presented in the book can help foster further research and cross-disciplinary interaction needed to surmount the barriers facing future generations of technology design.

  • 187.
    Fu, Ying
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Optical Properties of Quantum Dot Nano-composite Materials Studied by Solid-State Theory Calculations2012Ingår i: Handbook of Computational Chemistry / [ed] J. Leszczynski, Springer Berlin/Heidelberg, 2012, s. 869-899Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This chapter reviews the fundamental concepts of excitons and excitonic polaritons and their extraordinary optical properties in quantum dot nano-composite materials. By starting with the optical excitation of an exciton in the nanostructure we show that the effective dielectric constant of the nanostructure becomes significantly modified due to the exciton generation and recombination, resulting in high positive and negative dielectric constants. We also discuss single exciton generation by multiple photons and multiple exciton generation by single photon. All these nonlinear optical properties of quantum dot nano-composite materials offer novel possibilities and are expected to have deep impact in nanophotonics.

  • 188. Gao, Bin
    et al.
    Ruud, Kenneth
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Plasmon resonances in linear noble-metal chains2012Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, nr 19, s. 194307-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic excitations of three noble-metall chains-copper, silver, and gold-have been investigated at the time-dependent density functional theory level. The reduced single-electron density matrix is propagated according to the Liouville-von Neumann equation in the real-time domain after an impulse excitation. The propagation in the real-time domain enables us to investigate the formation and size evolution of electronic excitations in these metallic chains with different number of atoms, up to a total of 26 atoms. The longitudinal oscillations at lower excitation energies are dominated by s -> p transitions in these chains and have collective or central resonances, while the first peak involving d -> p transitions in the longitudinal mode appears at a higher excitation energy and shows collective resonances. In the transverse oscillations, there are in most cases d -> p transitions in each resonance, which can be attributed to either central or end resonances. Convergence of the oscillations, in particular those involving the collective and central resonances in the three noble-metal chains can only be observed for chains with 18 atoms or more. Different spectroscopic characteristics among these three metallic chains can be attributed to their different electronic structures, in particular the relativistic effects in the gold chains have a dramatic effect on their electronic structures and excitations.

  • 189. Gao, Bin
    et al.
    Ruud, Kenneth
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Shape-Dependent Electronic Excitations in Metallic Chains2014Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 24, s. 13059-13069Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic excitations of silver chains with different geometries (linear, circle, arc and zigzag chains) have been investigated at the time-dependent density functional theory level, by solving the equation of motion of the reduced single-electron density matrix in the real-time domain. A scaling parameter 0 <= lambda <= 1 has been introduced to adjust the two-electron contributions during propagation in the time domain in a way that allows us to distinguish different electronic excitations plasmon and single-particle excitations. The dipole responses, in particular the plasmon resonances of these metallic chains to an external delta-pulse, show a strong dependence on their geometric structures. In most cases, the dipole responses of these chains possess great tunability when altering their geometric parameters the radius of the circle and arc chains, and the bond angle of the zigzag chains. Some excitations in these chains also show a wide tunable excitation energy range, more than 1 eV, making it possible to fine-tune the excitations of the metallic chains at an atomic scale.

  • 190.
    Gao, Li
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Sun, Xianqiang
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Eriksson, Leif A.
    Modification of the anticancer drug tamoxifen to avoid CYP2D6 polymorphism2013Ingår i: Canadian journal of chemistry (Print), ISSN 0008-4042, E-ISSN 1480-3291, Vol. 91, nr 9, s. 916-924Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The prodrug tamoxifen (TAM) is the most widely used drug to treat breast cancer, and is metabolised to the active 4-hydroxy derivatives dominantly by hepatic CYP2D6. However, the application to patients with different polymorphic CYP2D6 has been under debate, because the efficacy of TAM is suspected to be suppressed in patients who have diminished CYP2D6 activity, resulting in inadequate active metabolites. We here propose modified structures, such as 4-methylTAM, which is highly possible to be activated by CYP3A, the most abundant CYP isoforms in the liver, whereby the genetic polymorphism of CYP2D6 is avoided. The diversity of CYP catalyzed metabolic paths for TAM and its derivatives are studied by quantum chemistry calculations on the reaction energies of the initial H atom abstraction steps. The ability of forming DNA adducts is compared through the formation enthalpy of the carbocation intermediate. The results suggest that the modified structures are safe with regard to forming DNA adducts and may be used as prodrugs in a wide range of patients, due to CYP3A, rather than CYP2D6, mediated activation.

  • 191.
    Gao, Li
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Eriksson, Leif A.
    More stable, more estrogenic: the SERM-ERα LBD complex2011Ingår i: Journal of Biophysical Chemistry, ISSN 2153-036X, E-ISSN 2153-0378, Vol. 2, nr 3, s. 233-243Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many synthetic selective estrogen receptor mo- dulators (SERMs) have been cocrystallized with the human estrogen receptor α ligand binding domain (ERα LBD). Despite stabilizing the same canonical inactive conformation of the LBD, most SERMs display different ligand-dependent pharmacological profiles. We show here that in-creased partial agonism of SERMs is associated with increased conformational stability of the SERM-LBD complexes, by investigation of dihy-drobenzoxathiin-based SERMs using molecular modelling techniques. Analyses of tamoxifen (TAM) and 4-hydroxytamoxifen (OHT) in complex with the LBD furthermore indicates that the conversion of TAM to OHT increases both the affinity to ERα and the partial agonism of the anti-cancer drug, which provides a plausible ex-planation of the counterintuitive results of TAM therapy.

  • 192.
    Gao, Li
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Eriksson, Leif A.
    Characterization of Agonist Binding to His524 in the Estrogen Receptor alpha Ligand Binding Domain2012Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, nr 16, s. 4823-4830Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The bioactivities of the natural steroidal estrogen 17 beta-estradiol (E-2), the synthetic estrogen diethylstilbestrol (DES), and the phytoestrogen genistein (GEN) are intimately associated with their binding to the estrogen receptor alpha ligand binding domain (ER alpha LBD) and accordingly allostery. Molecular modeling techniques have been performed on agonists in complex with the LBD, focusing on the pivotal role of His524 modeled as the epsilon-tautomer and the protonated form (depending on pH). It is found that E-2 binds to the active LBD with the aid of Leu525, showing existing stable patterns of an H-binding network with Glu419 via His524 in all models. The main difference seen in the effect is that the full agonists E-2 and DES have higher binding energies to the protonated His524 than the partial agonists GEN and Way-169916 (W), which is in line with noted experimental transcriptional activities. In conclusion, the study demonstrates that the phytoestrogen GEN interacts differently with the LBD than what E-2 and DES do, which explains the observed signaling differences.

  • 193.
    Gao, Li
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Eriksson, Leif A.
    Modification of the anticancerdrug tamoxifen to avoid CYP2D6 polymorphismManuskript (preprint) (Övrigt vetenskapligt)
  • 194. Ge, Jing
    et al.
    Zhang, Qun
    Jiang, Jun
    Geng, Zhigang
    Jiang, Shenlong
    Fan, Kaili
    Guo, Zhenkun
    Hu, Jiahua
    Chen, Zongwei
    Chen, Yang
    Wang, Xiaoping
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China, China.
    Bringing light into the dark triplet space of molecular systems2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 19, s. 13129-13136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A molecule or a molecular system always consists of excited states of different spin multiplicities. With conventional optical excitations, only the (bright) states with the same spin multiplicity of the ground state could be directly reached. How to reveal the dynamics of excited (dark) states remains the grand challenge in the topical fields of photochemistry, photophysics, and photobiology. For a singlet-triplet coupled molecular system, the (bright) singlet dynamics can be routinely examined by conventional femtosecond pump-probe spectroscopy. However, owing to the involvement of intrinsically fast decay channels such as intramolecular vibrational redistribution and internal conversion, it is very difficult, if not impossible, to single out the (dark) triplet dynamics. Herein, we develop a novel strategy that uses an ultrafast broadband white-light continuum as a excitation light source to enhance the probability of intersystem crossing, thus facilitating the population flow from the singlet space to the triplet space. With a set of femtosecond time-reversed pump-probe experiments, we report on a proof-of-concept molecular system (i.e., the malachite green molecule) that the pure triplet dynamics can be mapped out in real time through monitoring the modulated emission that occurs solely in the triplet space. Significant differences in excited-state dynamics between the singlet and triplet spaces have been observed. This newly developed approach may provide a useful tool for examining the elusive dark-state dynamics of molecular systems and also for exploring the mechanisms underlying molecular luminescence/photonics and solar light harvesting.

  • 195. Gejo, T.
    et al.
    Oura, M.
    Tokushima, T.
    Horikawa, Y.
    Arai, H.
    Shin, S.
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Kosugi, N.
    Resonant inelastic x-ray scattering and photoemission measurement of O2: Direct evidence for dependence of Rydberg-valence mixing on vibrational states in O 1 s → Rydberg states2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, nr 4, artikel-id 044310Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-resolution resonant inelastic x-ray scattering (RIXS) and low-energy photoemission spectra of oxygen molecules have been measured for investigating the electronic structure of Rydberg states in the O 1s → σ∗ energy region. The electronic characteristics of each Rydberg state have been successfully observed, and new assignments are made for several states. The RIXS spectra clearly show that vibrational excitation is very sensitive to the electronic characteristics because of Rydberg-valence mixing and vibronic coupling in O2. This observation constitutes direct experimental evidence that the Rydberg-valence mixing characteristic depends on the vibrational excitation near the avoided crossing of potential surfaces. We also measured the photoemission spectra of metastable oxygen atoms (O) from O2 excited to 1s → Rydberg states. The broadening of the 4p Rydberg states of O∗ has been found with isotropic behavior, implying that excited oxygen molecules undergo dissociation with a lifetime of the order of 10 fs in 1s → Rydberg states.

  • 196.
    Gel'mukhanov, Faris
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Liu, X. J.
    Prumper, G.
    Tanaka, T.
    Hoshino, M.
    Tanaka, H.
    Ueda, K.
    Young's double-slit experiment using two-center core-level photoemission: Photoelectron recoil effects2007Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 156, s. 265-269Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Core-level photoemission from N-2 can be considered an analogue of Young's double-slit experiment (YDSE) in which the double-slit is replaced by a pair of N 1s orbitals. The measured ratio between the 1 sigma(g) and 1 sigma(u) photoionization cross-sections oscillates as a function of photoelectron momentum, due to two-center YDSE interference, exhibiting a remarkable dependence on the vibrational sub-levels of the core ionized state. We theoretically demonstrate that the recoil of the photoelectron given to the ionized N atom strongly influences this interference pattern. The reason for this is that the momentum transfer affects the phases of the photoionization amplitudes.

  • 197. Gerasimov, V. S.
    et al.
    Ershov, A. E.
    Gavrilyuk, A. P.
    Karpov, S. V.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Polyutov, S. P.
    Suppression of surface plasmon resonance in Au nanoparticles upon transition to the liquid state2016Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, nr 23, s. 26851-26856Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Significant suppression of resonant properties of single gold nanoparticles at the surface plasmon frequency during heating and subsequent transition to the liquid state has been demonstrated experimentally and explained for the first time. The results for plasmonic absorption of the nanoparticles have been analyzed by means of Mie theory using experimental values of the optical constants for the liquid and solid metal. The good qualitative agreement between calculated and experimental spectra support the idea that the process of melting is accompanied by an abrupt increase of the relaxation constants, which depends, beside electron-phonon coupling, on electron scattering at a rising number of lattice defects in a particle upon growth of its temperature, and subsequent melting as a major cause for the observed plasmonic suppression. It is emphasized that observed effect is fully reversible and may underlie nonlinear optical responses of nanocolloids and composite materials containing plasmonic nanoparticles and their aggregates in conditions of local heating and in general, manifest itself in a wide range of plasmonics phenomena associated with strong heating of nanoparticles.

  • 198. Gerasimov, V. S.
    et al.
    Ershov, A. E.
    Karpov, S. V.
    Gavrilyuk, A. P.
    Zakomirnyi, Vadim I.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Rasskazov, I. L.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Polyutov, S. P.
    Thermal effects in systems of colloidal plasmonic nanoparticles in high-intensity pulsed laser fields [Invited]: publisher's note (vol 7,pg 555, 2017)2017Ingår i: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, nr 3, s. 799-799Artikel i tidskrift (Refereegranskat)
  • 199. Gerasimov, V. S.
    et al.
    Ershov, A. E.
    Karpov, S. V.
    Gavrilyuk, A. P.
    Zakomirnyi, Vadim
    KTH. Siberian Federal University, Russian Federation.
    Rasskazov, I. L.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Polyutov, S. P.
    Thermal effects in systems of colloidal plasmonic nanoparticles in high-intensity pulsed laser fields [Invited]2017Ingår i: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, nr 2, s. 555-568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied light induced processes in nanocolloids and composite materials containing ordered and disordered aggregates of plasmonic nanoparticles accompanied by their strong heating. A universal comprehensive physical model that combines mechanical, electrodynamical, and thermal interactions at nanoscale has been developed as a tool for investigations. This model was used to gain deep insight on phenomena that take place in nanoparticle aggregates under high-intensity pulsed laser radiation resulting in the suppression of nanoparticle resonant properties. Verification of the model was carried out with single colloidal Au and Ag nanoparticles and their aggregates.

  • 200.
    Gong, ZuYong
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China, China.
    Duan, Sai
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Tian, Guangjun
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Jiang, Jun
    Xu, Xin
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China, China.
    Infrared spectra of small anionic water clusters from density functional theory and wavefunction theory calculations2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 19, s. 12698-12707Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed systematic theoretical studies on small anionic water/deuterated water clusters W/D-n=2-6(-) at both density functional theory (B3LYP) and wavefunction theory (MP2) levels. The focus of the study is to examine the convergence of calculated infrared (IR) spectra with respect to the increasing number of diffuse functions. It is found that at the MP2 level for larger clusters (n = 4-6), only one extra diffuse function is needed to obtain the converged relative IR intensities, while two or three more sets of extra diffuse functions are needed for smaller clusters. Such behaviour is strongly associated with the convergence of the electronic structure of corresponding clusters at the MP2 level. It is striking to observe that at the B3LYP level, the calculated relative IR intensities for all the clusters under investigations are diverse and show no trend of convergence upon increasing the number of diffuse functions. Moreover, the increasing contribution from the extra diffuse functions to the dynamic IR dipole moment indicates that the B3LYP electronic structure also fails to converge. These results manifest that MP2 is a preferential theoretical method, as compared to the widely used B3LYP, for the IR intensity of dipole bounded electron systems.

1234567 151 - 200 av 778
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • 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