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  • 1. Amira, S.
    et al.
    Spangberg, D.
    Hermansson, Kersti
    KTH, Superseded Departments, Biotechnology.
    Derivation and evaluation of a flexible SPC model for liquid water2004In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 303, no 3, p. 327-334Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations of a new flexible water model are presented. The potential function is based on the simple point charge (SPC) model combined with an accurate experimental quartic intramolecular potential (CCL). This potential not only reproduces the key structural, dynamical and thermodynamical properties of liquid water, but also generates the correct values for both the absolute O-H vibrational frequency and the gas-to-liquid frequency shift. Thus, the model yields a value of ca. 3420 cm(-1) for the peak maximum of the anharmonic OH stretching band for liquid water (experiment 3400 cm(-1)) and a corresponding gas-to-liquid downshift of -300 cm(-1) (experiment -310 cm(-1)). The paper also emphasizes the importance of parameterizing correctly both the harmonic and anharmonic force constants in the gas-phase when developing flexible water models to be used in the liquid state.

  • 2. Baev, A
    et al.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Gelmukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    de Brito, N
    Bjorneholm, O
    Svensson, S
    Picturing molecular femtosecond processes through an ultra-fast controllable X-ray shutter2003In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 289, no 1, p. 51-56Article in journal (Refereed)
    Abstract [en]

    We show that frequency detuning in a resonant X-ray scattering experiment acts as an X-ray camera shutter by regulating the duration time of the scattering process. The camera shutter can be used to select processes at different time scales for observation. This is illustrated by a resonant Auger study of the ultra-fast dissociation of the core-excited HF molecule. We present experimental results and first principle simulations of the molecular fraction in the resonant Auger spectra of HF which is a dynamical parameter that well illustrates X-ray shutter controlled dissociation.

  • 3.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Sunchugashev, Dmitry A.
    Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Valiev, Rashid R.
    Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Minaev, Boris F.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Vibronic absorption spectra of the angular fused bisindolo- and biscarbazoloanthracene blue fluorophores for OLED applications2018In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 513, p. 105-111Article in journal (Refereed)
    Abstract [en]

    An in-depth analysis of the vibronic absorption spectra for the recently synthesized blue-fluorescent OLED emitters bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene has been carried out computationally at the density functional theory level within the Franck-Condon approximation. These molecules are characterized by extended and rich electronic absorption spectra with most absorption bands being of vibronic origin. The first excited singlet state of bis[(1,2)(5,6)]indoloanthracene compound demonstrates a clear observable double-peak vibronic progression for two different active modes in the absorption spectrum, while the S-2 state is vibronically inactive. In contrast, for the larger biscarbazolo[3,4-a:3',4'-h]anthracene compound the S-0 -> S-2 transition demonstrates well-resolved intense vibronic bands which overlap the less intense progressions of few modes in the S-0 -> S-1 transition. We have also found, that even the higher-lying and very intense S-0 -> S-4 and S-0 -> S-5 transitions for bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene, respectively, are characterized by clear vibronic progressions in excellent agreement with experimental spectra.

  • 4.
    Baryshnikov, Glib V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Cherkasy National University, Ukraine.
    Minaev, B. F.
    Baryshnikova, A. T.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu–-Cu distances2017In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 491, p. 48-55Article in journal (Refereed)
    Abstract [en]

    Three recently synthesized copper(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Dalton Trans., 2013, 42, 16878) have been computationally investigated by density functional theory within the broken symmetry approximation accounting for empirical dispersion corrections. A topological analysis of electron density distributions has been carried out using Bader's “quantum theory of atoms in molecules” formalism. The calculated values of spin-spin exchange for the studied dinuclear complexes indicate a very weak ferromagnetic coupling of the unpaired electrons in good agreement with experimental data. At the same time, the trinuclear copper(II) complex possesses a low-spin doublet ground state with one ferromagnetic and two antiferromagnetic spin projections between the triangular-positioned Cu2+ ions. The estimated values of the coupling constants for the spin-spin exchange in this trinuclear complex are in a good agreement with experimental observations. The calculations support a mechanism of exchange coupling through the aromatic links in these strongly spin-separated systems.

  • 5. Bondarchuk, Sergey V.
    et al.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Density functional study of ortho-substituted phenyl cations in polar medium and in the gas phase2011In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 389, no 1-3, p. 68-74Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations of several 2-X-substituted phenyl cations (X = 2-CHO, 2-CH(2)OH, 2-CHS, 2-CH=NH, 2-OCH=NH, 2-SCH=NH, 2-CH=CH-CH=CH(2), 2-CH=CH(2) and 2-NO(2)) have been carried out in the gas phase and in acetonitrile (MeCN) at the B3LYP/6-31G(d,p) level of theory. The stationary point geometry of these aryl cations have been found to be in strong dependency of the medium. In the gas phase, unexpected behavior of considered aryl cations takes place resulting in the rearrangement or ring closure reaction. Such the cyclization reaction is proceeding via the nearby atom of the substituent which appears in relative vicinity (up to similar to 3 angstrom) to the cationic center. Only in the case of 2-NO(2) derivative, the geometry optimization has lead to rearranged quazi-quinoid structure of the cation that, obviously, takes place because of instability of the ring formed. Scan of the potential energy surface (PES) of 2-nitrophenyl cation has displayed no any reaction path leading toward the rearranged structure. Thus, the impossibility of existing of the singlet state of 2-nitrophenyl cation in the gas phase has been offered. The singlet-triplet transition of 2-nitrophenyl cation has been discussed in terms of the spin-orbit coupling (SOC) effects.

  • 6. Carravetta, V.
    et al.
    Plashkevych, O.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    A screened static-exchange potential for core electron excitations2001In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 263, no 03-feb, p. 231-242Article in journal (Refereed)
    Abstract [en]

    We explore the use of a screened potential for static exchange calculations of core electron excitations, and to which extent this potential can relieve the main limitation of the static exchange method, namely the non-account of the residual screening in the presence of the excited electron. The screened potential is obtained by projecting the target state on a set of polarized orbitals, giving origin to a fully screened potential. Applications are presented and discussed for X-ray absorption spectra of a set of molecules of different size and type. It is found that with the little extra computational effort using the screened potential, the low-energy part of the spectra is generally improved, while the error in the term values are roughly of equal magnitude but of different sign compared to the normal static-exchange calculation. Various aspects of the screened and un-screened static-exchange approximations are analyzed in comparison with other techniques.

  • 7.
    Chen, Xing
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Cao, Zexing
    Department of Chemistry, Xiamen Univeristy.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Spectral character of intermediate state in solid-state photoarrangement of alpha-santonin2012In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 405, p. 40-45Article in journal (Refereed)
    Abstract [en]

    The vibronically resolved spectra of an intermediate and a product involved in the photoreaction of alpha-santonin have been explored by the density functional theory and the post-SCF methodologies, and a detailed comparison of theory with experiment was conducted to obtain reliable assignments to the observed spectra. The predicted emission energies of photosantonic acid and a topochemical product are found to match with the experimental values reasonably. The further calculations manifest that the absorption spectrum of photosantonic acid exhibits vibrationally resolved features, while the absorption band of topochemical product without vibrational resolution is opposite to the experimental observation. These new computational findings lead to a revised assignment to the observed bands and provide a basis for experimentalists to draw a convinced reaction mechanism for the alpha-santonin photorearrangement.

  • 8.
    de Almeida, Katia Júlia
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Hugosson, Håkan Wilhelm
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Cesar, Amary
    Univ Fed Minas Gerais, Dept Quim.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Modeling of EPR parameters of copper(II) aqua complexes2007In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 332, no 2-3, p. 176-187Article in journal (Refereed)
    Abstract [en]

    In this paper we report density functional theory calculations of the electronic g-tensor and hyperfine coupling constants of the copper dication in sixfold- and fivefold-coordination models of the first aqueous solvation sphere. The obtained results indicate that the electronic g-tensor of these copper complexes in combination with hyperfine coupling constants of copper in principle can be used to elucidate the coordination environment of the hydrated copper dication. In addition to these results, we have designed a methodology for accurate evaluation of electronic g-tensors and hyperfine coupling tensors in copper complexes, and demonstrate the applicability of this approach to copper dication aqua complexes.

  • 9.
    Edholm, Olle
    et al.
    KTH, Superseded Departments, Physics.
    Blomberg, C.
    Stretched exponentials and barrier distributions2000In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 252, no 02-jan, p. 221-225Article in journal (Refereed)
    Abstract [en]

    Non exponential relaxation in complex macromolecular systems may be the consequence of dispersedness giving rise to different free energy barriers for different molecules. An approximate analytic formula that relates the time derivative of the decaying function to a probability distribution for the barrier is derived. From this, so called stretched exponentials, e(-t beta),are obtained from barrier distributions with width k(B)T/beta in energy and some asymmetry towards low energies. They may be represented as double exponential functions. An exact general formula that relates the Fourier transforms of the barrier height distribution and the time decaying function is also derived. This is gives a much more stable method for the numerical determination of the barrier height distribution than direct inversion of the Laplace transform.

  • 10. Edvinsson, Tomas
    et al.
    Pschirer, Neil
    Schoneboom, Jan
    Eickemeyer, Felix
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Photoinduced electron transfer from a terrylene dye to TiO2: Quantification of band edge shift effects2009In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 357, no 1-3, p. 124-131Article in journal (Refereed)
    Abstract [en]

    A terrylene chromophore exhibiting a high extinction coefficient has been developed as a sensitizer for photovoltaic applications. The photophysical and photochemical properties of the dye were analyzed both experimentally and theoretically. Terrylene-sensitized nanocrystalline TiO2 solar cells yielded good photocurrents providing more than 60% in external quantum efficiency. The photoinduced electron transfer from the dye to TiO2 was found to be very sensitive to conduction band edge shifts in TiO2 induced, either by changes in the composition of the redox electrolyte or by UV-illumination. This sensitivity was observed in quantum efficiencies for photocurrent generation of terrylene-sensitized solar cells and in photoinduced absorption experiments. The conduction band shifts were quantified using charge extraction methods. The observed sensitivity of the injection efficiency suggests that photoinduced electron transfer occurs from the relaxed excited state, possibly due to poor electronic coupling between TMIMA excited states and TiO2 conduction band states.

  • 11. Farahani, Pooria
    et al.
    Lundberg, Marcus
    Karlsson, Hans
    Ab initio quantum mechanical calculation of the reaction probability forthe Cl þ PH2Cl ! ClPH2 þ Cl reaction2013In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 425, p. 134-140Article in journal (Refereed)
    Abstract [en]

    The SN2 substitution reactions at phosphorus play a key role in organic and biological processes. Quantummolecular dynamics simulations have been performed to study the prototype reactionCl þ PH2Cl ! ClPH2 þ Cl, using one and two-dimensional models. A potential energy surface, showingan energy well for a transition complex, was generated using ab initio electronic structure calculations.The one-dimensional model is essentially reflection free, whereas the more realistic two-dimensionalmodel displays involved resonance structures in the reaction probability. The reaction rate is almosttwo orders of magnitude smaller for the two-dimensional compared to the one-dimensional model. Energeticerrors in the potential energy surface is estimated to affect the rate by only a factor of two. Thisshows that for these types of reactions it is more important to increase the dimensionality of the modelingthan to increase the accuracy of the electronic structure calculation.

  • 12.
    Felicissimo, Viviane
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Minkov, Ivaylo
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Guimaraes, Freddy Fernandes
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Cesar, A.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    A theoretical study of the role of the hydrogen bond on core ionization of the water dimer2005In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 312, no 1-3, p. 311-318Article in journal (Refereed)
    Abstract [en]

    Motivated by the interest in using X-ray spectra for probing of hydrogen bonded networks we developed a quantum model for simulations of the electronic-vibrational profile of the X-ray core photoelectron spectrum of the water dimer. It is found that the potential surfaces of the donor and acceptor O1s core-ionized states of this system display a qualitative difference. Large gradients of the potential in the core ionized state along some intermolecular coordinates combined with small vibrational frequencies breaks down completely the harmonic approximation. The band profiles are therefore treated using a quasi-continuum approximation. The weak hydrogen bonding and the drastic change of water dimer potential under core ionization is responsible for the anomalously strong vibrational broadening: 0.4 eV for the acceptor band and 0.6 eV for the donor band. The core ionization of the donor oxygen is accompanied by proton transfer which should be observable in X-ray fluorescence or Auger spectra.

  • 13.
    García, Emilio Melero
    et al.
    KTH, Superseded Departments, Physics.
    Álvarez Ruiz, Jesús
    KTH, Superseded Departments, Physics.
    Erman, Peter
    KTH, Superseded Departments, Physics.
    Kivimäki, Antti Eerik
    KTH, Superseded Departments, Physics.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Rius Riu, Jaume
    KTH, Superseded Departments, Physics.
    Stankiewicz, Marek
    KTH, Superseded Departments, Physics.
    Veseth, V.
    Neutral dissociation of superexcited states in nitric oxide2003In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 293, no 1, p. 65-73Article in journal (Refereed)
    Abstract [en]

    Near-infrared dispersed fluorescence measurements of 13 different atomic multiplets of neutral atomic fragments from photon induced neutral dissociation processes in NO are reported. For excitation of the molecules narrow band synchrotron photons of energy 17.2-25.8 eV were used. Neither Rydberg series nor other molecular states in NO known so far can account for the collected data. From ab initio calculations we try to obtain more information regarding the NO precursor states, and the mechanism behind the observed neutral dissociation.

  • 14.
    Gelmukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Kimberg, Victor
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    X-ray Doppler spectroscopy of ultrafast fragmentation2004In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Chem. Phys., Vol. 299, p. 253-258Article in journal (Refereed)
    Abstract [en]

    Doppler effects are now commonly observed for Auger resonances of dissociating atoms in randomly oriented molecules. The physics behind the, yet not observed, Doppler effect for fixed-in-space molecules is different in that there will appear extra Doppler resonances resulting from the diffractional scattering of the Auger electrons by the surrounding atoms. It is argued that as these resonances will show maxima in the bond directions their measurement by current energy and angular resolved electron-ion coincidence experiments will provide structural probing. It is also shown that the electronic Doppler effect caused by nuclear vibrations can be observed also for bound nuclear states making use of electron-ion coincidence measurements. Optimal conditions for such measurements prevail when the scattering duration is comparable with a vibrational period.

  • 15. Herschend, Bjorn
    et al.
    Baudin, Micael
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    CO adsorption on CeO2(110) using hybrid-DFT embedded-cluster calculations2006In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 328, no 03-jan, p. 345-353Article in journal (Refereed)
    Abstract [en]

    The adsorption of CO on the CeO2 (110) surface has been studied using hybrid density functional theory (DFT) in the form of the B3LYP functional. In our calculations, both physisorption and chemisorption are observed. In the physisorption case, CO binds perpendicularly to a surface Ce ion. The adsorption energy is estimated to 0.1 eV and the CO stretching vibration becomes slightly blue-shifted (+9 cm(-1)), but the changes to the substrate and adsorbate structure are minimal. Test calculations using Moller-Plesset perturbation theory to the second order (MP2) suggest that dispersive interactions may be important in the case of CO physisorption on ceria. A chemisorption site was also found, where the CO molecule binds to two surface O ions, forming a surface carbonate species. Here, B3LYP predicts an adsorption energy of 2.1 eV and a red-shift of 470 cm(-1) for the CO stretching vibration.

  • 16.
    Hu, Wei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Duan, Sai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Lin, L. -L
    Ma, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Shandong Normal University, China.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Vibrational identification for conformations of trans-1,2-bis (4-pyridyl) ethylene in gold molecular junctions2015In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 453-454, p. 20-25Article in journal (Refereed)
    Abstract [en]

    The surface-enhanced Raman scattering (SERS) spectroscopy and inelastic electron tunneling spectroscopy (IETS) are employed to study trans-1,2-bis (4-pyridyl) ethylene (BPE)/gold system. Both junction and complex forms are considered for the SERS simulations. It is predicted that the peak at 1581 cm-1 is more intense in the junction forms than that in the complex forms. Time dependent density functional theory calculations show that the relative intensity is mainly controlled by the excitation energy derivative respect to the normal modes, and the total intensity is governed by the excitation energy of the excited states. The CH bending modes dominate the IET spectra when BPE adsorbed on the flat gold surfaces. While, the pyridyl ring deformation modes are more active when BPE adsorbed on the edge of the gold clusters. For BPE adsorbed on the tip of gold clusters, the pyridyl ring and CC stretching modes show significant contribution to the IET spectra.

  • 17.
    Jansson, Emil
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Jha, Prakash Chandra
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Chain length dependence of singlet and triplet excited states of oligofluorenes: A density functional study2007In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 336, no 2-3, p. 91-98Article in journal (Refereed)
    Abstract [en]

    Using time dependent density functional theory, we investigate the chain length dependence of the energies of excited states of a series of conjugated 9,9-dihexylfluorene-2,7-diyl oligomers. Excited state optimization reveals that upon excitation the dihedral angle between two adjacent monomer units moves towards zero, forming a planar structure within the oligomer. The calculated energies of the optical transitions in absorption, fluorescence, phosphorescence and triplet-triplet absorption are compared with recently reported experimental data. The calculated as well as experimentally reported energies involved seem to saturate very fast as the chain length increases. The energy dispersion and saturation indicates that the triplet ground state is somewhat more confined than the first singlet excited state. Our calculated energies agree well with the experimental findings where available, showing small but systematic deviations.

  • 18.
    Jansson, Emil
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Jha, Prakash Chandra
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Density functional study of triazole and thiadiazole systems as electron transporting materials.2006In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 330, no 02-jan, p. 166-171Article in journal (Refereed)
    Abstract [en]

    Density functional theory has been used for the calculation of electronic structures, vertical electron affinities and intramolecular reorganization energies for bis-aryl substituted triazole and thiadiazole. The results obtained on the basis of the theoretical calculations indicate that the HOMO and LUMO energies of the substituted molecules can be tuned by changing the substituents as well as by changing the center atom. These changes lead to energy shifts in the order of 2-2.5 eV. The calculation and comparison of vertical electron affinities and intramolecular reorganization energies confirm that thiadiazole systems are interesting for electron transport properties. Taking a lesson from these substitutions, we further model the systems by twisting the molecular units along the central dihedral angle starting from the ideal structure and compare their HOMO-LUMO gap, electron affinity and reorganization energy. We find that by having simple substituents at proper positions one can control the reorganization energy, which in turn indicates that electron transport properties can be tuned.

  • 19.
    Jansson, Emil
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Minaev, Boris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Schrader, Sigurd
    echnische Fachhochschule Wildau, University of Applied Sciences.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Time-dependent density functional calculations of phosphorescence parameters for fac-tris(2-phenylpyridine) iridium2007In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 333, no 03-feb, p. 157-167Article in journal (Refereed)
    Abstract [en]

    fac-Tris(2-phenylpyridine) iridium [fac-Ir(PPY)(3)] produces strong phosphorescence and has therefore been used as materials in organic light emitting diodes to overcome the efficiency limit imposed by the formation of triplet excitons. Accounting for this circumstance we present in this paper a theoretical study of phosphorescence in the Ir(PPY)(3) complex. The spin-orbit coupling effects and the radiative lifetime in the high temperature limit (T) are calculated by time-dependent density functional theory using quadratic response technology in order to elucidate the main mechanism of the phosphorescence. It is found that the orbital structure of the T, state has a localized character and that the T1 -> S0 transition is determined mostly by charge transfer from one of the ligands to the metal. At the vertical S-0-T-1 excitation the triplet state is highly delocalized among all three ligands and has a mixed pi pi* and metal-to-ligand charge transfer character. The intensity borrowing from the S-0 to S-5 transitions is mostly responsible for the strong phosphorescence emission from the x and y spin sublevels. Our results concord with the experimental data on temperature and magnetic field dependence of the phosphorescence kinetics. The calculated radiative lifetime in the high temperature limit agrees well with the measured decay times (2 mu s) accounting for negligible non-radiative quenching of the lowest triplet state.

  • 20. Jonsson, D.
    et al.
    Norman, P.
    Ågren, H.
    Single determinant calculations of excited state polarizabilities1997In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 224, no 2-3, p. 201-214Article in journal (Refereed)
    Abstract [en]

    We apply response theory to simulate excited state polarizabilities emphasizing the possibility to do so by means of optimization of a ground state single determinant only. The excited state polarizabilities are given by the double residues of the cubic response functions. A set of molecules with varying ground state configurations and properties have been considered: water, ozone, formaldehyde, ethylene, butadiene, cyclobutadiene, pyridine, pyrazine and s-tetrazine. The results have been compared to excited state experiments where available and with linear response calculations of the multi-determinant optimized excited state. It is shown that calculations of excited state polarizabilities based on a ground state optimized single determinant work well for most of the cases investigated. This contention is exemplified by the fact that the gas phase value from an electrochromism experiment for the polarizability of the 11B2 excited state of formaldehyde is better reproduced by ground state cubic response theory than by the corresponding separate state linear response function calculation, and by that the calculations call for an experimental reinvestigation of the excited state polarizabilities of s-tetrazine. A few prerequisites are given: The excited state should be isolated in energy, the ordering of the main contributing states should be reproduced, and the geometric conformation of the excited state in question should not be very different from the ground state geometry. The computational and formal advantages of the approach are discussed. © 1997 Elsevier Science B.V.

  • 21. Karaush, Nataliya N.
    et al.
    Valiev, Rashid R.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Tomsk State Univ.
    Baryshnikov, Gleb V.
    Minaev, Boris F.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    DFT simulation of the heteroannelated octatetraenes vibronic spectra with the Franck-Condon and Herzberg-Teller approaches including Duschinsky effect2015In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 459, p. 65-71Article in journal (Refereed)
    Abstract [en]

    Calculations of vibronic structure in the electronic absorption spectra are carried out for the series of heteroannelated octatetraenes on the basis of density functional theory method. Both Franck-Condon and Herzberg-Teller approaches have been used for estimation of frequency and intensity of vibronic bands in the simulated absorption spectra with respect to the S-0 -> S-1 electronic transition. The key result discussed in this work is that the electronic transition into the first singlet excited states is vibronicallyactive in the absorption spectra for all studied circulenes in a good agreement with experimental observations. We have confirmed our previous assumption that the first (low-lying) weak absorption maximum in the spectra of tetra-tert-butyltetraoxa[8] circulene and dithieno[3,4-b: 3',4'-d]thiophene-annelated cyclooctatetraene can be assigned just for the S-0 -> S-1 transition which produce the next more intense vibronic satellite. In the case of aza[8] circulenes the S-0 -> S-1 transition is symmetry allowed and the corresponding vibronic bands are less intense relative to 0-0 band. (C) 2015 Elsevier B.V. All rights reserved.

  • 22. Loboda, O.
    et al.
    Minaev, B.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Schimmelpfennig, B.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Ruud, K.
    Jonsson, D.
    Ab initio calculations of zero-field splitting parameters in linear polyacenes2003In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 286, no 1, p. 127-137Article in journal (Refereed)
    Abstract [en]

    The results of ab initio calculations of zero-field splitting (ZFS) parameters are presented for the linear polyacenes from benzene to pentacene. We show how the electron spin-spin (SS) parameters can be efficiently obtained from restricted high-spin open-shell wave functions (ROHF), and present calculations of these, comparing with the results of a recent multi-configurational self-consistent field approach. The SS parameters are obtained from electron SS coupling strengths evaluated as expectation values over the wave functions and from state-to-state spin-orbit (SO) interactions. The results for the two lowest triplet states of naphthalene demonstrate that excellent values can be obtained even using moderate basis sets in the wave function, indicating that this technique can be used to obtain reliable ZFS parameters of aromatic compounds. Electron correlation is, however, not negligible; by accounting for full pi-electron correlation the ZFS parameters are in considerably better agreement with experiment than the ROHF results. The ROHF method still reproduced the qualitative trend in the polyacene series in which the ZFS parameters are reduced with increasing size of the pi-conjugation. We confirm that the SS coupling contributions completely determine the D and E parameters for the lowest triplet state of the linear polyacenes and that the SO coupling contributions are small. Geometry optimization of the lowest triplet state was found to be fairly significant for the calculated D and E values; these were reduced by about 30% and 40%, respectively, when the geometry was changed from the ground-state singlet to the triplet-excited state optimized geometry, with the latter values being in better agreement with experiment. The present calculations predict that the second triplet state of naphthalene is very unusual, as it has a negative zero-field splitting, implying an altered ordering of the spin sublevels compared to what is common in aromatic systems.

  • 23. Loboda, O.
    et al.
    Tunell, I.
    Minaev, B.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Theoretical study of triplet state properties of free-base porphin2005In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 312, no 03-jan, p. 299-309Article in journal (Refereed)
    Abstract [en]

    This paper presents results and analysis of various properties of the triplet state of free-base porphin (FBP) as calculated by density-functional theory. The radiative lifetime of phosphorescence lines and microwave signals in optical detection of magnetic resonance (ODMR) spectra are obtained using the B3LYP hybrid density-functional and the quadratic response method. The zero-field splitting (ZFS) in the lowest triplet state, a B-3(2 omega) of FBP is calculated as an expectation value of spin-spin coupling operator using the self-consistent field wavefunction. The second-order contribution to US from the spin-orbit coupling operator is found to be almost negligible. The interpretation of the ODMR spectrum is completed by computing the hyperfine tensors of the N-14, C-13 and hydrogen atoms in the lowest triplet state. The most intense phosphorescence emission corresponds to the T-z-spin-sublevel of the a B-3(2u) state, where the z-axis lies in the N-H direction of the FBP molecule in a qualitative agreement with ODMR data. The results indicate that the observed decay of the lowest triplet state of FBP molecule is determined by non-radiative deactivation. The calculated radiative rate constant for the T-z-spin-sublevel k(z),= 2.65 x 10(-3) s(-1) is in agreement with the value k(z) similar or equal to 2 x 10(-3) s(-1), estimated by van Dorp et al. [W. van Dorp, W. Schoemaker, M. Soma, J. van der Waals, Mol. Phys. 30 (1975) 1701] from kinetic analysis of microwave-induced fluorescent signals. The correct prediction of the spin quantization axis of the most active spin sublevel and of its radiative lifetime in the lowest triplet state of the FBP molecule is taken as a proof of capability of the quadratic response time-dependent density-functional theory.

  • 24. Minaev, B. F.
    et al.
    Jonsson, D.
    Norman, P.
    Ågren, H.
    Character and spectra of triplet states in short polyenes1995In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 194, no 1, p. 19-31Article in journal (Refereed)
    Abstract [en]

    Multi-configuration quadratic response calculations with complete account of the spin-orbit coupling operator are performed to study the singlet-triplet absorption and emission spectra of the short polyenes; ethene, trans-1,3-butadiene and trans-1,3,5-hexatriene molecules. The emission spectra are calculated from geometry optimized triplet states. The missing phosphorescence in these compounds are explained as a combination of small oscillator strengths and vibrational quenching. © 1995 Elsevier Science B.V. All rights reserved.

  • 25. Minaev, B.
    et al.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Theoretical DFT study of phosphorescence from porphyrins2005In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 315, no 3, p. 215-239Article in journal (Refereed)
    Abstract [en]

    Geometrical structure of free-base porphin (H2P) and Mg- and Zn-porphyrins together with their vibrational frequencies and vibronic intensities in phosphorescence are investigated by density functions theory (DFT) with the standard B3LYP functional. These molecules have a closed-shell singlet ground state (S-0) and low-lying triplet (T-1) excited states of pi pi* type. The S-0-T-1 transition probability and radiative lifetime of phosphorescence (tau(p)) of these molecules are calculated by time-dependent DFT utilizing quadratic response functions for account of spin-orbit coupling (SOC) and electric-dipole transition moments including displacements along active vibrational modes. The infrared and Raman spectra in the ground singlet and first excited triplet states are also studied for proper assignment of vibronic patterns. The long radiative lifetime of free-base porphin phosphorescence (tau(p) similar to 360 s at low temperature limit, 4.2 K) gets considerably shorter for the metalloporphyrins. An order of magnitude reduction of tau(p) is predicted for Mg-porphyrin but no change of phosphorescence polarization is found. A forty times enhancement of the radiative phosphorescence rate constant is obtained for Zn-porphyrin in comparison with the H2P molecule which is accompanied by a strong change of polarization and spin-sublevel radiative activity. A strong vibronic activity of free-base porphin phosphorescence is found for the b(2g) mode at 430 cm(-1), while the 679 and 715 cm(-1) vibronic bands of b(3g) symmetry are less active. These and other out-of-plane vibrations produce considerable changes in the radiative constants of different spin sublevels of the triplet state; they also promote the S-1 --> T-1 intersystem crossing. Among the in-plane vibrations the a(g) mode at 1614 cm(-1) is found very active; it produces a long progression in the phosphorescence spectrum. The time-dependent DFT calculations explain the effects of the transition metal atom on phosphorescence of porphyrins and reproduce differences in their phosphorescence and EPR spectra.

  • 26. Minaev, Boris
    et al.
    Norman, Patrick
    Jonsson, Dan
    Ågren, Hans
    Response theory calculations of singlet-triplet transitions in molecular nitrogen1995In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 190, p. 11-29Article in journal (Refereed)
  • 27.
    Minaev, Boris
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    De Angelis, Filippo
    Theoretical design of phosphorescence parameters for organic electro-luminescence devices based on iridium complexes2009In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 358, no 3, p. 245-257Article in journal (Refereed)
    Abstract [en]

    Tithe-dependent density functional theory with quadratic response methodology is used in order to calculate and compare spin-orbit coupling effects and the main mechanism of phosphorescence of the neutral Ir(ppy)(3) and cationic [Ir(bpy)(3)](3+) tris-iridium compounds, [Ir(ppy)(2)(bpy)](+) and [Ir(2-phenylpyridine)(2)(4,4'-tert-butyl-2,2'-bipyridine](+) complexes, including also the recently synthesised [Ir(2-phenylpyridine)(2)(4,4'-dimethylamino-2,2'-bipyridine](+) and [Ir(2,4-difluorophenylpyridine)(2)(4,4'-dimethylamino-2,2'-bipyridine](+) dyes, where ppy = 2-phenylpyridine and bpy = 2,2'-bipyridine ligands. Comparison with the symmetric, lighter and more studied [Ru(bpy)(3)](2+) and [Rh(bpy)(3)](3+) complexes is also resented. Variations in lifetimes for Ir(ppy)(3) and [Ir(bpy)(3)](3+) dyes as well as for the mixed cationic complexes are well reproduced by the quadratic response method. All the ortho-metalated iridium compounds exhibit strong phosphorescence, which is used in organic light-emitting diodes (OLEDs) to overcome the efficiency limit imposed by the formation of triplet excitons. The results from the first principle theoretical analysis of phosphorescence have helped to clarify the connections between the main features of electronic structure and the photo-physical properties of the studied heavy organometallic OLED materials.

  • 28. Muller, C.
    et al.
    Freysoldt, C.
    Baudin, M.
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    An ab initio study of CO adsorption on ceria(110)2005In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 318, no 3, p. 180-190Article in journal (Refereed)
    Abstract [en]

    Hartree-Fock and DFT calculations are reported for the CO/CeO2(110) surface system. The electron density, electrostatic potential, atomic charges and projected electronic density of states have been calculated from an ECP-and-point-charge-embedded cluster model and is compared with periodic calculations. The agreement between the two surface models is reasonably good. A number of weakly bonding CO adsorption sites were found, with E-ads (BSSE-corrected) ranging from 0.01 to 0.22 eV per adsorbed molecule. The two most favourable sites are found in the vicinity of surface cerium ions, with the CO molecule oriented in a tilted fashion, C-end down. The surface-induced CO stretching vibrational frequency shifts on these sites are a redshift of approximate to-30 cm(-1) and a blueshift of approximate to 25 cm(-1), respectively.

  • 29. Norman, P.
    et al.
    Cronstrand, P.
    Ericsson, J.
    Theoretical study of linear and nonlinear absorption in platinum-organic compounds2002In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 285, no 2-3, p. 207-220Article in journal (Refereed)
    Abstract [en]

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

  • 30. Norman, P.
    et al.
    Jonsson, D.
    Vahtras, O.
    Ågren, H.
    Non-linear electric and magnetic properties obtained from cubic response functions in the random phase approximation1996In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 203, no 1, p. 23-42Article in journal (Refereed)
    Abstract [en]

    We derive cubic response functions in the Random Phase Approximation for calculations of non-linear frequency-dependent properties of molecules, and demonstrate an implementation of these functions using efficient computational algorithms. Illustrations are given by calculations of the frequency-dependent second hyperpolarizabilities, the frequency-dependent excited state polarizabilities and the three-photon transition amplitudes of the para-nitroaniline molecule, and by calculations of the frequency dependent magnetic second hyperpolarizabilities and their anisotropies for the first row hydrides isoelectronic with neon.

  • 31. Plashkevych, O
    et al.
    Privalov, Timofei
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Carravetta, V
    Ruud, K
    On the validity of the equivalent cores approximation for computing X-ray photoemission and photoabsorption spectral bands2000In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 260, no 1-2, p. 11-28Article in journal (Refereed)
    Abstract [en]

    We evaluate the performance of the equivalent cores (Z + 1) approximation for computing core photoemission and photoabsorption spectral bands versus full self-consistent field optimizations. Franck-Condon factors are obtained using the linear coupling model with the multi-dimensional vibronic coupling constants computed from analytical calculations of the ground state frequencies and normal coordinates, and excited state energy gradients evaluated at the ground state equilibrium geometry. We use carbon monoxide, formaldehyde, chloromethanes and some monosubstituted benzenes for the purpose. Considering other inherent approximations in the calculations, we find that the equivalent core model works well for band shapes and comparatively better for excitations of strong modes and ionization of deeper core levels. The approximation also works somewhat better for photoemission than for discrete photoexcitation.

  • 32.
    Rahm, Martin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Dinitraminic acid (HDN) isomerization and self-decomposition revisited2008In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 348, no 1-3, p. 53-60Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) and the ab initio based CBS-QB3 method have been used to study possible decomposition pathways of dinitraminic acid HN(NO2)(2) (HDN) in gas-phase. The proton transfer isomer of HDN, O2NNN(O)OH, and its conformers can be formed and converted into each other through intra- and intermolecular proton transfer. The latter has been shown to proceed substantially faster via double proton transfer. The main mechanism for HDN decomposition is found to be initiated by a dissociation reaction, splitting of nitrogen dioxide from either HDN or the HDN isomer. This reaction has an activation enthalpy of 36.5 kcal/mol at the CBS-QB3 level, which is in good agreement with experimental estimates of the decomposition barrier.

  • 33.
    Rudberg, Elias
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Computation of Franck-Condon factors for many-atom systems: simulated photoelectron spectra of formic acid isotopologues2004In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 302, no 1-3, p. 217-228Article in journal (Refereed)
    Abstract [en]

    Simulated photoelectron spectra of the four formic acid isotopologues HCOOH, HCOOD, DCOOH and DCOOD are reported. The simulations are based on computed multidimensional harmonic Franck-Condon factors (FCFs) for transitions from the ground state of the neutral molecule to the two lowest electronic states of the cation. The geometrical parameters and force constants used in the Franck-Condon analysis have been obtained at the B3LYP/6-311 +G(3df,2p) level of theory. The results are compared with well-resolved experimental spectra, and good agreement between simulated and experimental spectra is found, in particular for the first PES band. Using the computed FCFs, the vibrational fine structure of the first two bands of the experimental spectra is analyzed, and vibrational frequencies for the two cationic states are extracted from the experimental data.

  • 34.
    Salek, Pawel
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Helgaker, T.
    Saue, T.
    Linear response at the 4-component relativistic density-functional level: application to the frequency-dependent dipole polarizability of Hg, AuH and PtH22005In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 311, no 1-2, p. 187-201Article in journal (Refereed)
    Abstract [en]

    We report the implementation and application of linear response density-functional theory (DFT) based on the 4-component relativistic Dirac-Coulomb Hamiltonian. The theory is cast in the language of second quantization and is based on the quasienergy formalism (Floquet theory), replacing the initial state dependence of the Runge-Gross theorem by periodic boundary conditions. Contradictions in causality and symmetry of the time arguments are thereby avoided and the exchange-correlation potential and kernel can be expressed as functional derivatives of the quasienergy. We critically review the derivation of the quasienergy analogues of the Hohenberg-Kohn theorem and the Kohn-Sham formalism and discuss the nature of the quasienergy exchange-correlation functional. Structure is imposed on the response equations in terms of Hermiticity and time-reversal symmetry. It is observed that functionals of spin and current densities, corresponding to time-antisymmetric operators, contribute to frequency-dependent and not static electric properties. Physically, this follows from the fact that only a time-dependent electric field creates a magnetic field. It is furthermore observed that hybrid functionals enhance spin polarization since only exact exchange contributes to anti-Hermitian trial vectors. We apply 4-component relativistic linear response DFT to the calculation of the frequency-dependent polarizability of the iso-electronic series Hg, AuH and PtH2. Unlike for the molecules, the effect of electron correlation on the polarizability of the mercury atom is very large, about 25%. We observe a remarkable performance of the local-density approximation (LDA) functional in reproducing the experimental frequency-dependent polarizability of this atom, clearly superior to that of the BLYP and B3LYP functionals. This allows us to extract Cauchy moments (S(-4) = 382.82 and S(-6) = 6090.89 a.u.) that we believe are superior to experiment since we go to higher order in the Cauchy moment expansion.

  • 35. Sauge, Sebastien
    et al.
    Valiron, P.
    Collisional survival of antiprotonic helium atoms2001In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 265, no 1, p. 47-61Article in journal (Refereed)
    Abstract [en]

    We investigate the collisional survival of antiprotonic (p) over bar He+ atomcules in pure helium from a detailed ab initio analysis of their intermolecular interaction. After averaging over classical (p) over bar orbits, we attribute the collisional stability of thermalized atomcules to the existence of a high activation barrier due to Pauli repulsion. Our model predicts the reduction of the barrier for outer (p) over bar orbits, thus accounting for the quenching of high n states by He atoms. We also investigate the thermalization stage of newly formed atomcules from a classical trajectory Monte Carlo approach. Our results support the destruction of the states with n greater than or equal to 41, as well as the strong depopulation of all n < 41 layers, with a quenching rate of 50% at least. Assuming a statistical distribution of newly formed atomcules with respect to their initial angular momentum, we account for the 3% observed trapping fraction of metastable states. <(c)> 2001 Elsevier Science B.V. All rights reserved.

  • 36. Sauge, Sebastien
    et al.
    Valiron, P.
    Quenching of cold antiprotonic helium atoms by collisions with H-2 molecules2002In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 283, no 3, p. 433-453Article in journal (Refereed)
    Abstract [en]

    We investigate the collisional quenching of cold metastable antiprotonic atomcules [(p) over bar He+], by HZ molecules in view of the recent state-resolved measurements at CERN. Firstly, we determine ab initio the 6-D intermolecular interaction between the four (anti)nuclei at the CCSD(T)/CP level. After averaging the interaction over the fast (p) over bar orbits, we exhibit reactive channels and activation barriers below few 100 muE(h). Hence, we account qualitatively for the order of magnitude and (n,l) dependence of the quenching cross-sections measured at 30 K, after estimating tunneling probabilities. We also account for the lower quenching efficiency by deuterium. However improving this overall agreement would require the determination of numerous finer contributions. We monitor the saturation of electronic correlation with larger basis sets; we estimate the importance of dynamical relaxation effects; and we stress the role of quantum vibrational and rotational delocalization for the light (p, (p) over bar) nuclei. The latter vibrational corrections lower the barriers, while the rotational H-2 averaging defavours isotropic para-H-2 (J = 0). As a result, we mainly attribute the quenching at 30 K to ortho-H-2 (J = 1). Additional experiments at other temperatures and with para-H-2 would further constrain this orthopara quenching selectivity, and provide an ideal four-body benchmark for further chemical physics investigations (including tunneling effects, collision-induced Auger decay, etc).

  • 37. SEKI, K
    et al.
    KARLSSON, Ulf O
    KTH, School of Information and Communication Technology (ICT).
    ENGELHARDT, R
    KOCH, EE
    SCHMIDT, W
    INTRAMOLECULAR BAND MAPPING OF POLY(PARA-PHENYLENE) VIA UV PHOTOELECTRON-SPECTROSCOPY OF FINITE POLYPHENYLS1984In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 91, no 3, p. 459-470Article in journal (Refereed)
  • 38. SEKI, K
    et al.
    UENO, N
    KARLSSON, Ulf O
    KTH, School of Information and Communication Technology (ICT).
    ENGELHARDT, R
    KOCH, EE
    VALENCE BANDS OF ORIENTED FINITE LINEAR-CHAIN MOLECULAR-SOLIDS AS MODEL COMPOUNDS OF POLYETHYLENE STUDIED BY ANGLE-RESOLVED PHOTOEMISSION1986In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 105, no 1-2, p. 247-265Article in journal (Refereed)
  • 39. Spangberg, D.
    et al.
    Hermansson, Kersti
    KTH, Superseded Departments, Biotechnology.
    The solvation of Li+ and Na+ in acetonitrile from ab initio-derived many-body ion-solvent potentials2004In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 300, no 03-jan, p. 165-176Article in journal (Refereed)
    Abstract [en]

    Several Li--(+) and Na+-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/ TZV++(d,p) level for distorted ion-(MeCN)(n) clusters with n = 1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Bohm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li+(MeCN) and Na+(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li+ ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na+ close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common.

  • 40.
    Ueda, K.
    et al.
    KTH, School of Biotechnology (BIO).
    Liu, X.-J.
    Prumper, G.
    Lischke, T.
    Tanaka, T.
    Hoshino, M.
    Tanaka, H.
    Minkov, Ivaylo
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Kimberg, Victor
    KTH, School of Biotechnology (BIO).
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Role of the recoil effect on two-center interference in x-ray photoionization2006In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 329, no 1-3, p. 329-337Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectra of the N-2 molecule are studied both experimentally and theoretically in the extended energy region up to 1 keV. The ratio of the photoionization cross sections for the gerade and ungerade core levels displays a modulation in the high energy region caused by the two-center interference, as predicted by Cohen and Fano (CF) in 1966. The physical background of this CF effect is the same as in Young's double-slit experiment. We have found that the interference pattern deviates significantly from the CF prediction. The origin of such a breakdown of the CF formula is the scattering of the photoelectron inside the molecule and the momentum transfer from the emitted fast photoelectron to the nuclei. Usually the recoil effect is small. We show that the electron recoil strongly affects the two-center interference pattern. Both stationary and dynamical aspects of the recoil effect shed light on the role of the momentum exchange in the two-center interference.

  • 41.
    Vahtras, Olav
    et al.
    KTH, Superseded Departments, Biotechnology.
    Loboda, O.
    Minaev, B.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Ruud, K.
    Ab initio calculations of zero-field splitting parameters2002In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 279, no 03-feb, p. 133-142Article in journal (Refereed)
    Abstract [en]

    We present calculations of electron spin-spin (SS) coupling strengths evaluated as expectation values over multi-configuration and restricted high-spin self-consistent field wave functions. Together with the spin-orbit (SO) configuration interaction methodology, this enables us to analyze the full spin Hamiltonian including the zero-field splitting (ZFS) parameters of the triplet state. The calculated ZFS parameters include both the SS coupling to first order and SO coupling to second order of perturbation theory. The relative importance of these two contributions is strongly system dependent. In the lowest triplet state of the benzene molecule, the main ZFS parameter - the D parameter - is determined entirely by the SS coupling, with D calculated to be 0.1583 cm(-1). In contrast, the calculated D parameter in the X(3)Sigma(g)(-) ground state of the oxygen molecule (3.77 cm(-1)) includes a large one-center SS contribution (D-SS = 1.455 cm(-1)) but an even larger SO coupling contribution (D-SO = 2.315 cm(-1)). ZFS parameters for molecular oxygen excited states, A(3)Sigma(u)(+) and B(3)Sigma(u)(-), which belong to Hund's case (b), are also calculated. A large negative D value (-10.2 cm(-1)) for the A(3)Sigma(u)(+) state is to 90% determined by the D-SO contribution, while the Schumann-Runge state spin splitting is mainly determined by SS coupling. The calculated values for benzene and oxygen are in good agreement with data from EPR and rotational fine-structure spectra. The applicability of response theory is with this contribution expanded to include the calculation of the SS coupling of the spin Hamiltonian, complementing the previous implementations of hyperfine A- and g-tensors.

  • 42. Wennmalm, Stefan
    et al.
    Edman, Lars
    Rigler, Rudolf
    Non-ergodic behaviour in conformational transitions of single DNA molecules1999In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Chemical PhysicsArticle in journal (Refereed)
1 - 42 of 42
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