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  • 1.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Agnarsson, Björn
    Bidermane, Ieva
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Noël, Quentin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sun, Chenghua
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 17, p. 174702-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and scanning tunneling microscopy. Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and an inhomogeneous charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I(root 3x root 3) or Pt(111)-I(root 7x root 7), and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.

  • 2.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Shariati, M. Nina
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 8, p. 084705-Article in journal (Refereed)
    Abstract [en]

    We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the pi-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; pi-system and the central atom.

  • 3.
    Ai, Yue-Jie
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Zhang, Feng
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Cui, Gang-Long
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fang, Wei-Hai
    Ultrafast deactivation processes in the 2-aminopyridine dimer and the adenine-thymine base pair: Similarities and differences2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 6, p. 064302-Article in journal (Refereed)
    Abstract [en]

    2-aminopyridine dimer has frequently been used as a model system for studying photochemistry of DNA base pairs. We examine here the relevance of 2-aminopyridine dimer for a Watson-Crick adenine-thymine base pair by studying UV-light induced photodynamics along two main hydrogen bridges after the excitation to the localized (1)pi pi(*) excited-state. The respective two-dimensional potential-energy surfaces have been determined by time-dependent density functional theory with Coulomb-attenuated hybrid exchange-correlation functional (CAM-B3LYP). Different mechanistic aspects of the deactivation pathway have been analyzed and compared in detail for both systems, while the related reaction rates have also be obtained from Monte Carlo kinetic simulations. The limitations of the 2-aminopyridine dimer as a model system for the adenine-thymine base pair are discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3464485]

  • 4.
    Alfredsson, Y.
    et al.
    Department of Physics, Uppsala University.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nilson, K.
    Department of Physics, Uppsala University.
    Åhlund, J.
    Department of Physics, Uppsala University.
    Kjeldgaard, L.
    MAX-lab, University of Lund.
    Nyberg, Mats
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Mårtensson, N.
    Department of Physics, Uppsala University.
    Sandell, A.
    Department of Physics, Uppsala University.
    Puglia, C.
    Department of Physics, Uppsala University.
    Siegbahn, H.
    Department of Physics, Uppsala University.
    Electronic structure of a vapor-deposited metal-free phthalocyanine thin film2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 21Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.

  • 5. Al-Khalili, A
    et al.
    Thomas, R
    Ehlerding, A
    Hellberg, F
    Geppert, W D
    Zhaunerchyk, V
    af Ugglas, M
    Larsson, M
    Uggerud, E
    Vedde, J
    Adlhart, C
    Semaniak, J
    Kaminska, M
    Zubarev, R A
    Kjeldsen, F
    Andersson, P U
    Österdahl, Fabian
    KTH, Superseded Departments, Physics.
    Bednarska, V A
    Paal, A
    Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 12, p. 5700-5708Article in journal (Refereed)
    Abstract [en]

    Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.

  • 6. Amft, Martin
    et al.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Influence of the cluster dimensionality on the binding behavior of CO and O(2) on Au(13)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 2, p. 024312-Article in journal (Refereed)
    Abstract [en]

    We present an ab initio density functional theory study of the binding behavior of CO and O(2) molecules to two-and three-dimensional isomers of Au(13) in order to investigate the potential catalytic activity of this cluster towards low-temperature CO oxidation. First, we scanned the potential energy surface of Au(13) and studied the effect of spin-orbit coupling on the relative stabilities of the 21 isomers we identified. While spin-orbit coupling increases the stability of the three-dimensional more than the two-dimensional isomers, the ground state structure at 0 K remains planar. Second, we systematically studied the binding of CO and O(2) molecules onto the planar and three-dimensional structures lowest in energy. We find that the isomer dimensionality has little effect on the binding of CO to Au(13). O(2), on the other hand, binds significantly to the three-dimensional isomer only. The simultaneous binding of multiple CO molecules decreases the binding energy per molecule. Still, the CO binding remains stronger than the O(2) binding. We did not find a synergetic effect due to the co-adsorption of both molecular species. On the three-dimensional isomer, we find O(2) dissociation to be exothermic with an dissociation barrier of 1.44 eV.

  • 7. Amira, S.
    et al.
    Spangberg, D.
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    OD vibrations and hydration structure in an Al3+(aq) solution from a Car-Parrinello molecular-dynamics simulation2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 10Article in journal (Refereed)
    Abstract [en]

    The optimized geometry, energetics, and vibrational properties of Al(D2O)(n)(3+) clusters, with n=1,2,4, and 6, have been studied using plane waves, different local basis sets, different methodologies [density-functional theory, MP2, CCSD(T)], and different functionals (BLYP, PBE). Moreover, Car-Parrinello molecular-dynamics (MD) simulations using the BLYP functional, plane waves, and the Vanderbilt ultrasoft pseudopotentials have been performed for an aqueous Al3+ solution with 1 ion and 32 D2O molecules in a periodic box at room temperature, studied for 10 ps. The cluster calculations were performed to pinpoint possible shortcomings of the electronic structure description used in the Car-Parinello MD (CPMD) simulation. For the clusters, the hydration structure and interaction energies calculated with the 'BLYP/plane-wave' approach agree well with high-level ab initio methods but the exchange-correlation functional introduces errors in the OD stretching frequencies (both in the absolute values and in the ion-induced shifts). For the aqueous solution, the CPMD simulation yields structural properties in good agreement with experimental data. The CPMD-simulated OD stretching vibrational band for the first-shell water molecules around Al3+ is strongly downshifted by the influence of the ion and is compared with experimental data from the literature. To make such a comparison meaningful, the influences of a number of systematic effects have been addressed, such as the exchange-correlation functional, the fictitious electron mass, anharmonicity effects, and the small box size in the simulation. Each of these factors (except the last one) is found to affect the OD frequency by 100 cm(-1) or more. The final corrected frequencies agree with experiment within similar to 30 cm(-1) for bulk water but are too little downshifted for the first-shell Al3+(aq) water molecules (by similar to 200 cm(-1)).

  • 8. Andersson, E.
    et al.
    Niskanen, Johannes
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Hedin, L.
    Eland, J. H. D.
    Linusson, P.
    Karlsson, L.
    Rubensson, J. -E
    Carravetta, V.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Feifel, R.
    Core-valence double photoionization of the CS2 molecule2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 9, p. 094305-Article in journal (Refereed)
    Abstract [en]

    Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy.

  • 9. Andersson, L. Mauritz
    Quantum dynamics using a discretized coherent state representation: An adaptive phase space method2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 3, p. 1158-1165Article in journal (Refereed)
    Abstract [en]

    We introduce a discretized coherent state representation (DCSR) for quantum dynamics. Expansion of a wave function in the nonorthogonal slightly overcomplete set is made with an identity operator computed using an iterative refinement method. Calculating the inverse of the overlap matrix is not necessary. The result is an accurate and efficient representation, where you only put basis functions in the region of phase space where the wave function is nonvanishing. Compared to traditional spatial grid methods, fewer grid points are needed. The DCSR can be viewed as an application of the Weyl-Heisenberg frame and extends it into a useful computational method. A scheme for fully quantum mechanical propagation is constructed and applied to the realistic problem of highly excited vibration in the heavy diatomic molecule Rb-2. Compared to split-operator propagation in a conventional spatial grid, an order of magnitude longer time steps can be taken and fewer grid points are needed. The computational effort scales linearly with the number of basis functions. Nonreflecting boundary conditions are a natural property of the representation and is illustrated in a model of predissociation.

  • 10.
    Anghel, Clara
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dong, Qian
    Isotopic investigation of the transport of oxygen species in Y-stabilized zirconiaIn: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Other academic)
  • 11. Baev, A.
    et al.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Macak, P.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    General theory for pulse propagation in two-photon active media2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 117, no 13, p. 6214-6220Article in journal (Refereed)
    Abstract [en]

    The propagation of laser pulses of different lengths in nonlinear media of organic absorbers is described starting out from a recently suggested dynamical theory for two-photon absorption (TPA) of molecules in solutions [J. Opt. Soc. Am. B 19, 937 (2002)]. The roles of saturation effects and pulse duration on the suppression of TPA are emphasized. The numerical simulations of the pulse propagation are performed for a two-photon active charge transfer molecule using molecular parameters obtained from first principle calculations.

  • 12. Baraldi, Alessandro
    et al.
    Vesselli, Erik
    Bianchettin, Laura
    Comelli, Giovanni
    Lizzit, Silvano
    Petaccia, Luca
    de Gironcoli, Stefano
    Locatelli, Andrea
    Mentes, T. Onur
    Aballe, Lucia
    Weissenrieder, Jonas
    Lund University.
    Andersen, Jesper N.
    The (1x1)-> hexagonal structural transition on Pt(100) studied by high-energy resolution core level photoemission2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 16Article in journal (Refereed)
    Abstract [en]

    The (1 x 1)-> quasihexagonal (HEX) phase transition on a clean Pt(100) surface was investigated by monitoring the time evolution of the Pt4f(7/2) core level photoemission spectra. The spectral component originating from the atoms forming the (1 x .1) metastable unreconstructed surface was found at -570 +/- 20 meV with respect to the bulk peak. Ab initio calculations based on density functional theory confirmed the experimental assignment. At temperatures above 370 K, the (1 x 1) phase irreversibly reverts to the more stable HEX phase, characterized by a surface core level shifted component at -185 +/- 40 meV. By analyzing the intensity evolution of the core level components, measured at different temperatures in the range of 393-475 K, we determined the activation energy of the phase transformation, E=0.76 +/- 0.04 eV. This value is considerably lower than the one previously determined by means of low energy electron diffraction. Possible reasons for this discrepancy are discussed.

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

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

  • 14. Behringer, H.
    et al.
    Eichhorn, Ralf
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Brownian dynamics simulations with hard-body interactions: Spherical particles2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 16, p. 164108-Article in journal (Refereed)
    Abstract [en]

    A novel approach to account for hard-body interactions in (overdamped) Brownian dynamics simulations is proposed for systems with non-vanishing force fields. The scheme exploits the analytically known transition probability for a Brownian particle on a one-dimensional half-line. The motion of a Brownian particle is decomposed into a component that is affected by hard-body interactions and into components that are unaffected. The hard-body interactions are incorporated by replacing the affected component of motion by the evolution on a half-line. It is discussed under which circumstances this approach is justified. In particular, the algorithm is developed and formulated for systems with space-fixed obstacles and for systems comprising spherical particles. The validity and justification of the algorithm is investigated numerically by looking at exemplary model systems of soft matter, namely at colloids in flow fields and at protein interactions. Furthermore, a thorough discussion of properties of other heuristic algorithms is carried out.

  • 15.
    Belonoshko, Anatoly B.
    et al.
    KTH, Superseded Departments, Physics.
    LeBacq, O.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Molecular dynamics study of phase transitions in Xe2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 117, no 15, p. 7233-7244Article in journal (Refereed)
    Abstract [en]

    A full account is given of our recent theoretical discovery [A. B. Belonoshko, R. Ahuja, and B. Johansson, Phys. Rev. Lett. 87, 165505 (2001)] of the fcc-bcc transition in Xe at high pressure and temperature. The interaction model and method for calculating phase boundaries are exhaustively tested by independent methods. The model was carefully checked against experimental data and results of ab initio molecular dynamics and it was found to perform very well. The two-phase method employed for finding the melting transition was compared with the robust thermodynamic approach and was found to provide data in exact agreement with the latter. The deviation of the calculated melting curve from the experimental one is quite tolerable at low pressures. After a reinterpretation of the experimental data, our results are also in good agreement with recent diamond anvil cell experiments. At a pressure of around 25 GPa and a temperature of about 2700 K, we find a triple fcc-bcc-liquid point. The fcc-bcc boundary is calculated without reference to the experimental data, in contrast to our previous work, and found to be in nice agreement with previous calculations as well as with the experimental data points, which, however, were interpreted as melting. Our finding concerning the fcc-bcc transition is confirmed by the direct molecular dynamics simulation of the fcc, bcc, and liquid phases in the same computational cell. In this simulation, it was observed that while the fcc phase melts, the bcc structure solidifies. Since Xe is a typical rare-gas solid, the fcc-bcc transition can now be expected for a number of other van der Waals systems, first of all in Ar and Kr. Our finding suggests, that the transition from close packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated. The performed thorough test of methods and models in this study leads us to suggest that the original interpretation of experimental results is erroneous.

  • 16.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, N. V.
    Bastea, S.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Shock wave propagation in dissociating low-Z liquids: D-22005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 12Article in journal (Refereed)
    Abstract [en]

    We present direct molecular dynamics simulations of shock wave propagation in liquid deuterium for a wide range of impact velocities. The calculated Hugoniot is in perfect agreement with the gas-gun data as well as with the most recent experimental data. At high impact velocities we observe a smearing of the shock wave front and propagation of fast dissociated molecules well ahead of the compressed region. This smearing occurs due to the fast deuterium dissociation at the shock wave front. The experimental results are discussed in view of this effect.

  • 17.
    Bergström, Lars Magnus
    KTH, Superseded Departments, Chemistry.
    Derivation of expressions for the spontaneous curvature, mean and Gaussian bending constants of thermodynamically open surfactant monolayers and bilayers2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 118, no 3, p. 1440-1452Article in journal (Refereed)
    Abstract [en]

    We have derived expressions for the spontaneous curvature H-0, the mean and Gaussian bending constants, k(c) and (k) over bar (c), respectively, for a surfactant film of finite thickness that is open in a thermodynamic sense. Geometrical packing constraints are taken into account and give rise to explicit large and important contributions to k(c), (k) over bar (c), and k(c)H(0). From its contribution to the latter quantity we may deduce that surfactant aggregates (micelles, vesicles, microemulsion droplets) are expected to dramatically increase their size with increasing surfactant tail length. Moreover, the coupling between free energy contributions related to surfactant head group and tail with geometrical packing constraints give rise to dominant terms on the form 2xi(p)H(0), where xi(p) is the thickness of a planar film, in the expressions for k(c). In the case of repulsive head group effects that favor a large spontaneous curvature, such as electrostatics, these terms raise k(c) and thus increase the rigidity of the film. Due to the constraint of constant free monomer chemical potentials, the composition of the film becomes a function of curvature. As a result, the ability of a surfactant film to have different surfactant compositions in differently curved parts (e.g., inner and outer layer of a vesicle, central parts and end caps of rod or threadlike micelles, etc.) may considerably reduce k(c), whereas (k) over bar

  • 18.
    Bergström, Lars Magnus
    KTH, Superseded Departments, Chemistry.
    Thermodynamics of anisotropic surfactant micelles. I. The influence of curvature free energy on the micellar size and shape2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, no 13, p. 5559-5568Article in journal (Refereed)
    Abstract [en]

    A novel theory for the structural behavior of surfactant micelles is expounded. The micelles are considered to be generally shaped as triaxial tablets with distinct thickness width and length, respectively, and may become spherical, spherocylindrical or disk-shaped in the special cases where two or more of the dimensions are equal. It is demonstrated that the average width and length of a tablet-shaped micelle with a fixed thickness is mainly determined by two constants, k(1) and k(2), related to the first and second order correction in curvature of the micellar end caps. The size of the micelles is found to be mainly determined by k(1), whereas k(2) influences the shape, i.e., the length-to-width ratio, of the micelles so that the micellar size increases with increasing k(1) and the length-to-width ratio decreases with increasing k(2). Hence, large positive values of k(2) promote the formation of tablets rather than very long spherocylinders. An additional parameter related to the curvature of the straight cylindrical rims may influence the structure of the tablet-shaped micelles insofar k(2) is close to or below zero.

  • 19.
    Bergström, Lars Magnus
    KTH, Superseded Departments, Chemistry.
    Thermodynamics of anisotropic surfactant micelles. II. A molecular interpretation of the micellar curvature free energy2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, no 13, p. 5569-+Article in journal (Refereed)
    Abstract [en]

    Explicit expressions have been derived for the two curvature constants k(1) and k(2) that mainly influence the size and shape, respectively, of generally shaped micelles (triaxial tablets with a thickness < width < length). It is found that geometrical packing constraints, together with an unfavorable hydrocarbon/water interfacial tension gamma(hc/w), give rise to a large and positive contribution to both k(1) and k(2) that increases with the micellar thickness (equivalent to surfactant tail length) as well as with gamma(hc/w). The constant k(1) that mainly influence the size of the micelles may be brought down by electrostatics to values where rather small micelles are able to form. However, electrostatics also have a tendency to increase the constant k(2) that mainly affects the length-to-width ratio of the micelles so that the smaller micelles are predicted to be rather disklike, i.e., with a low length-to-width ratio. In addition, residual head group effects as well as the free energy contribution due to the hydrocarbon chains may influence the micellar size and shape. In particular, it is demonstrated that mixing of two surfactants reduces k(2) and promotes the formation of elongated micelles with a large length-to-width ratio whereas k(1), and thus the overall size of the micelles, is only slightly influenced. The effect of mixing is predicted to increase with increasing asymmetry between the surfactants mixed in the micelles with respect to head group size and charge number as well as hydrophobic tail volume.

  • 20.
    Besharat, Zahra
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Halldin Stenlid, Joakim
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Marks, Kess
    Önsten, Anneli
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Johnson, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Öström, Henrik
    Weissenrieder, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Dehydrogenation of methanol on Cu2O(100) and (111)2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 24Article in journal (Refereed)
    Abstract [en]

    Adsorption and desorption of methanol on the (111) and (100) surfaces of  Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120–620 K, in combination with density functional theorycalculations and sum frequency generation spectroscopy. The bare (100) surfaceexhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this  surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surfaceoxygen.

  • 21. Bidermane, I.
    et al.
    Luder, J.
    Boudet, S.
    Zhang, T.
    Ahmadi, Sareh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Grazioli, C.
    Bouvet, M.
    Rusz, J.
    Sanyal, B.
    Eriksson, O.
    Brena, B.
    Puglia, C.
    Witkowski, N.
    Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 23, p. 234701-Article in journal (Refereed)
    Abstract [en]

    Using Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy, the thickness dependent formation of Lutetium Phthalocyanine (LuPc2) films on a stepped passivated Si(100)2x1 reconstructed surface was studied. Density functional theory (DFT) calculations were employed to gain detailed insights into the electronic structure. Photoelectron spectroscopy measurements have not revealed any noticeable interaction of LuPc2 with the H-passivated Si surface. The presented study can be considered to give a comprehensive description of the LuPc2 molecular electronic structure. The DFT calculations reveal the interaction of the two molecular rings with each other and with the metallic center forming new kinds of orbitals in between the phthalocyanine rings, which allows to better understand the experimentally obtained NEXAFS results.

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

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

  • 23. Bittererova, M.
    et al.
    Ostmark, H.
    Brinck, Tore
    KTH, Superseded Departments, Chemistry.
    A theoretical study of the azide (N-3) doublet states. A new route to tetraazatetrahedrane (N-4): N+N-3 -> N-42002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 116, no 22, p. 9740-9748Article in journal (Refereed)
    Abstract [en]

    The potential energy surfaces for the low-lying doublet states of the azide radical (N-3) have been computed at the complete active space self-consistent field (CASSCF) level with the CAS(15,12) active space. The cc-pVTZ and aug-cc-pVTZ basis sets have been employed throughout the present work. Energies, geometries and harmonic frequencies were determined for the N-3 linear ground electronic state ((2)Pi(g)), a stable C-2v ring structure (B-2(1)), and a C-s transition state ((2)A(')) connecting the ring and linear structures. Other N-3 (C-2v) stationary points ((2)A(2), B-2(1), and (2)A(1)) have been characterized, as well. The vertical excitation energies for the doublet excited states of the N-3 linear ((2)Pi(g)) and stable ring (B-2(1)) isomers were calculated using CASSCF and multireference configuration interaction [MRCI-SD(Q)] methods. A new route to tetraazatetrahedrane [N-4(T-d)] has been proposed on the N-4 singlet potential energy surface within C-s symmetry. MRCI-SD(Q) calculations predict that N-4 (T-d) can be formed from atomic nitrogen in the D-2 state and N-3 (C-2v, B-2(1)) in a barrierless exothermic reaction. The energy difference (D-0) is 135.4 kcal/mol at the MRCI-SD(Q) level.

  • 24.
    Brandt, Erik G.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Edholm, Olle
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Stretched exponential dynamics in lipid bilayer simulations2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 11, p. 115101-Article in journal (Refereed)
    Abstract [en]

    The decay of fluctuations in fluid biomembranes is strongly stretched and nonexponential on nanometer lengthscales. We report on calculations of structural correlation functions for lipid bilayer membranes from atomistic and coarse-grained molecular dynamics simulations. The time scales extend up to microseconds, whereas the linear size of the largest systems is around 50 nm. Thus, we can cover the equilibrium dynamics of wave vectors over two orders of magnitude (0.2-20 nm(-1)). The time correlations observed in the simulations are best described by stretched exponential functions, with exponents of 0.45 for the atomistic and 0.60 for the coarse-grained model. Area number density fluctuations, thickness fluctuations, and undulations behave dynamically in a similar way and have almost exactly the same dynamics for wavelengths below 3 nm, indicating that in this regime undulations and thickness fluctuations are governed by in-plane density fluctuations. The out-of-plane height fluctuations are apparent only at the longest wavelengths accessible in the simulations (above 6 nm). The effective correlation times of the stretched exponentials vary strongly with the wave vector. The variation fits inverse power-laws that change with wavelength. The exponent is 3 for wavelengths smaller than about 1.25 nm and switches to 1 above this. There are indications for a switch to still another exponent, 2, for wavelengths above 20 nm. Compared to neutron spin-echo (NSE) experiments, the simulation data indicate a faster relaxation in the hydrodynamic limit, although an extrapolation of NSE data, as well as inelastic neutron scattering data, is in agreement with our data at larger wave vectors.

  • 25.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Carniato, S.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Functional and basis set dependence of K-edge shake-up spectra of molecules2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 18, p. 184316-Article in journal (Refereed)
    Abstract [en]

    A straightforward approach for computing the K -edge shake-up spectra of molecules based on equivalent core-hole linear response theory at both Hartree-Fock and density functional theory levels is proposed. Benchmark calculations have been performed to explore its sensitivity to different types of functionals and basis sets for the carbon 1s shake-up spectra of benzene and metal-free phthalocyanine (H2 Pc). A very good agreement with previous theoretical and experimental works for the benzene molecule has been obtained for all the functionals and basis sets tested. Electron correlation is found to be essential for a good description of the H2 Pc system, whose experimental C 1s shake-up spectrum is best reproduced by the hybrid density functional.

  • 26.
    Brena, Barbara
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Characterization of the electronic structure of C50Cl10 by means of soft x-ray spectroscopies2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 24, p. 244305-1-244305-4Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the last synthesized fullerene molecule, the C50Cl10, has been characterized by theoretical simulation of x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and near-edge x-ray-absorption fine structure. All the calculations were performed at the gradient-corrected and hybrid density-functional theory levels. The combination of these techniques provides detailed information about the valence band and the unoccupied molecular orbitals, as well as about the carbon core orbitals.

  • 27.
    Brena, Barbara
    et al.
    KTH, Superseded Departments, Biotechnology.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Electronic structures of azafullerene C48N122003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 14, p. 7139-7144Article in journal (Refereed)
    Abstract [en]

    Two recently proposed low-energy azafullerene C48N12 isomers have been theoretically characterized using x-ray spectroscopies. The x-ray photoelectron spectroscopy, the near-edge absorption fine structure, the x-ray emission spectroscopy, and the ultraviolet photoelectron spectroscopy for both isomers have been predicted at the gradient-corrected density functional theory level. These spectroscopies together give a comprehensive insight of the electronic structure on the core, valence, and unoccupied orbitals. They have also provided a convincing way for identifying the isomer structures.

  • 28.
    Brumboiu, Iulia Emilia
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Prokopiou, G.
    Kronik, L.
    Brena, B.
    Valence electronic structure of cobalt phthalocyanine from an optimally tuned range-separated hybrid functional2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 4, article id 044301Article in journal (Refereed)
    Abstract [en]

    We analyse the valence electronic structure of cobalt phthalocyanine (CoPc) by means of optimally tuning a range-separated hybrid functional. The tuning is performed by modifying both the amount of short-range exact exchange (α) included in the hybrid functional and the range-separation parameter (γ), with two strategies employed for finding the optimal γ for each α. The influence of these two parameters on the structural, electronic, and magnetic properties of CoPc is thoroughly investigated. The electronic structure is found to be very sensitive to the amount and range in which the exact exchange is included. The electronic structure obtained using the optimal parameters is compared to gas-phase photo-electron data and GW calculations, with the unoccupied states additionally compared with inverse photo-electron spectroscopy measurements. The calculated spectrum with tuned γ, determined for the optimal value of α = 0.1, yields a very good agreement with both experimental results and with GW calculations that well-reproduce the experimental data.

  • 29.
    Busson, B.
    et al.
    Univ Paris Saclay, Univ Paris Sud, CNRS, Lab Chim Phys, Batiment 201 P2, F-91405 Orsay, France..
    Dalstein, Laetitia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. Laboratoire de Chimie Physique, CNRS, University of Paris-Sud, Université Paris-Saclay, Bâtiment 201 P2, Orsay, France.
    Nonlinear optical response of a gold surface in the visible range: A study by two-color sum-frequency generation spectroscopy. II. Model for metal nonlinear susceptibility2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 3, article id 034701Article in journal (Refereed)
    Abstract [en]

    We present a modeling of the nonlinear optical response of a metal surface in order to account for recent experimental results from two-color Sum-Frequency Generation (SFG) experiments on gold. The model allows calculating the surface and bulk contributions and explicitly separates free and bound electron terms. Contrary to the other contributions, the perpendicular surface component is strongly model-dependent through the surface electron density profiles. We consider three electron density schemes at the surface, with free and bound electrons overlapping or spilling out of the bulk, for its calculation. The calculated SFG signals from the metal rely only on bulk quantities and do not need an explicit definition of the density profiles. In the particular case of gold, when the free electrons overlap with the bound ones or spill out of the bulk, the free electron response completely dominates through the perpendicular surface terms. When the bound electrons spill out, the situation is more balanced, still in favor of the free electrons, with lower amplitudes and different dispersion line shapes. As for silver, the free electron contributions dominate and the calculated slow amplitude growth from blue to red follows the experimental trends.

  • 30. Callaghan, P. T.
    et al.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Diffusion-diffusion correlation and exchange as a signature for local order and dynamics2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 8, p. 4032-4038Article in journal (Refereed)
    Abstract [en]

    We demonstrate the use of new two-dimensional nuclear magnetic resonance experiments in the examination of local diffusional anisotropy under conditions of global isotropy. The methods, known as diffusion-diffusion correlation spectroscopy and diffusion exchange spectroscopy, employ successive pairs of magnetic field gradient pulses, with signal analysis using two-dimensional inverse Laplace transformation. Diffusional anisotropy is measured for water molecules in a polydomain lamellar phase lyotropic liquid crystal, 40 wt % nonionic surfactant C10E3 (C10H21O(CH2CH2O)(6)H) in H2O.

  • 31. Cao, Jun
    et al.
    Fang, Qiu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fang, Wei-Hai
    Photoisomerization mechanism of 4-methylpyridine explored by electronic structure calculations and nonadiabatic dynamics simulations2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 4, p. 044307-Article in journal (Refereed)
    Abstract [en]

    In the present paper, different electronic structure methods have been used to determine stationary and intersection structures on the ground (S-0) and (1)pi pi* (S-2) states of 4-methylpyridine, which is followed by adiabatic and nonadiabatic dynamics simulations to explore the mechanistic photoisomerization of 4-methylpyridine. Photoisomerization starts from the S-2((1)pi pi*) state and overcomes a small barrier, leading to formation of the prefulvene isomer in the S-0 state via a S-2/S-0 conical intersection. The ultrafast S-2 -> S-0 nonradiative decay and low quantum yield for the photoisomerization reaction were well reproduced by the combined electronic structure calculation and dynamics simulation. The prefulvene isomer was assigned as a long-lived intermediate and suggested to isomerize to 4-methylpyridine directly in the previous study, which is not supported by the present calculation. The nonadiabatic dynamics simulation and electronic structure calculation reveal that the prefulvene isomer is a short-lived intermediate and isomerizes to benzvalene form very easily. The benzvalene form was predicted as the stable isomer in the present study and is probably the long-lived intermediate observed experimentally. A consecutive light and thermal isomerization cycle via Dewar isomer was determined and this cycle mechanism is different from that reported in the previous study. It should be pointed out that formation of Dewar isomer from the S-2((1)pi pi*) state is not in competition with the isomerization to the prefulvene form. The Dewar structure observed experimentally may originate from other excited states.

  • 32. Carniato, S.
    et al.
    Selles, P.
    Journel, L.
    Guillemin, R.
    Stolte, W. C.
    El Khoury, L.
    Marin, T.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Lindle, D. W.
    Simon, M.
    Thomson-resonant interference effects in elastic x-ray scattering near the Cl K edge of HCl2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 9, p. 094311-Article in journal (Refereed)
    Abstract [en]

    We experimentally observed interference effects in elastic x-ray scattering from gas-phase HCl in the vicinity of the Cl Kedge. Comparison to theory identifies these effects as interference effects between non-resonant elastic Thomson scattering and resonant Raman scattering. The results indicate the non-resonant Thomson and resonant Raman contributions are of comparable strength. The measurements also exhibit strong polarization dependence, allowing an easy identification of the resonant and non-resonant contributions.

  • 33. Carniato, Stéphane
    et al.
    Taïeb, Richard
    Kukk, Edwin
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Brena, Barbara
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    N-K near edge x-ray absorption fine structures of acetonitrile in gas phase2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 21, p. 214301-Article in journal (Refereed)
    Abstract [en]

     The dynamic processes of N(1s) core-hole excitation in gas-phase CH3CN molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N-K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of nu((CN)) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.

  • 34. Carravetta, V.
    et al.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Jensen, H. J. A.
    Ab initio calculations of molecular resonant photoemission spectra2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, no 18, p. 7790-7798Article in journal (Refereed)
    Abstract [en]

    An ab initio method for calculations of molecular resonant photoemission (RPE) spectra is described. The method includes a multicenter expansion of both the dipole matrix element-direct emission-and the Hamiltonian matrix element between the resonant state and the autoionizing states-resonant emission. These quantities are relevant for the description of the process both in the two-step model, where the spectrum is computed at the resonance energy only, and in the one-step model where, by a K-matrix approach, the direct-to-resonant interference is taken into account and the electronic line profile is fully described. The resonant two-electron matrix elements are evaluated over the core-excited relaxed orbitals with the outgoing Auger electron orbital expanded on an augmented multicentered Gaussian basis set. Stieltjes imaging is shown to work excellently for such Gaussian basis sets giving correct continuum normalization matrix elements even for RPE electron energies as high as 100-1000 eV. A numerical investigation is carried out for the participator decay of the C 1s --> pi* and O 1s --> pi* states of CO.

  • 35. Castleton, C. W. M.
    et al.
    Kullgren, J.
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 24Article in journal (Refereed)
    Abstract [en]

    We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U approximate to 3 eV and that the degree of localization reaches a maximum at similar to 6 eV for LDA+U or at similar to 5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U > 0 eV, but the band structure is similar to LDA+U.) The best overall choice is U approximate to 6 eV with LDA+U and approximate to 5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both CeO2 and Ce2O3, with and without vacancies, is hard to find.

  • 36.
    Chen, Xing
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ruud, K.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Role of zero-point vibrational corrections to carbon hyperfine coupling constants in organic pi radicals2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 5, p. 054310-Article in journal (Refereed)
    Abstract [en]

    By analyzing a set of organic pi radicals, we demonstrate that zero-point vibrational corrections give significant contributions to carbon hyperfine coupling constants, in one case even inducing a sign reversal for the coupling constant. We discuss the implications of these findings for the computational analysis of electron paramagnetic spectra based on hyperfine coupling constants evaluated at the equilibrium geometry of radicals. In particular, we note that a dynamical description that involves the nuclear motion is in many cases necessary in order to achieve a semi-quantitatively predictive theory for carbon hyperfine coupling constants. In addition, we discuss the implications of the strong dependence of the carbon hyperfine coupling constants on the zero-point vibrational corrections for the selection of exchange-correlation functionals in density functional theory studies of these constants.

  • 37. Coriani, Sonia
    et al.
    Host, Stinne
    Jansik, Branislav
    Thogersen, Lea
    Olsen, Jeppe
    Jorgensen, Poul
    Reine, Simen
    Pawlowski, Filip
    Helgaker, Trygve
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Linear-scaling implementation of molecular response theory in self-consistent field electronic-structure theory2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, no 15, p. 11930-11935Article in journal (Refereed)
    Abstract [en]

    A linear-scaling implementation of Hartree-Fock and Kohn-Sham self-consistent field theories for the calculation of frequency-dependent molecular response properties and excitation energies is presented, based on a nonredundant exponential parametrization of the one-electron density matrix in the atomic-orbital basis, avoiding the use of canonical orbitals. The response equations are solved iteratively, by an atomic-orbital subspace method equivalent to that of molecular-orbital theory. Important features of the subspace method are the use of paired trial vectors (to preserve the algebraic structure of the response equations), a nondiagonal preconditioner (for rapid convergence), and the generation of good initial guesses (for robust solution). As a result, the performance of the iterative method is the same as in canonical molecular-orbital theory, with five to ten iterations needed for convergence. As in traditional direct Hartree-Fock and Kohn-Sham theories, the calculations are dominated by the construction of the effective Fock/Kohn-Sham matrix, once in each iteration. Linear complexity is achieved by using sparse-matrix algebra, as illustrated in calculations of excitation energies and frequency-dependent polarizabilities of polyalanine peptides containing up to 1400 atoms.

  • 38. Cronstrand, P.
    et al.
    Jansik, Branislav
    KTH, Superseded Departments, Biotechnology.
    Jonsson, D.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Density functional response theory calculations of three-photon absorption2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 19, p. 9239-9246Article in journal (Refereed)
    Abstract [en]

    Three-photon absorption probabilities delta(3PA) have been calculated through application of a recently derived method for cubic response functions within density functional theory (DFT). Calculations are compared with Hartree-Fock (HF) and with a coupled cluster hierarchy of models in a benchmarking procedure. Except for cases having intermediate states near resonance, density functional theory is demonstrated to be in sufficient agreement with the highly correlated methods in order to qualify for predictions of delta(3PA). For the larger systems addressed, a set of acceptor A and donor D substituted pi-conjugated systems formed by trans-stilbene and dithienothiophene (DTT), we find noticeable differences in the magnitude of delta(3PA) between HF and DFT, although similar trends are followed. It is shown that the dipolar structures, TS-AD and DTT-AD, have substantially larger delta(3PA) than other types of modifications which is in accordance with observations for two-photon absorption. This is the first application of density functional theory to three-photon absorption beyond the use of few-state models.

  • 39. Cronstrand, P.
    et al.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Effects of dipole alignment and channel interference on two-photon absorption cross sections of two-dimensional charge-transfer systems2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 117, no 24, p. 11102-11106Article in journal (Refereed)
    Abstract [en]

    The relationship between two-photon absorption cross sections and the architecture of donor-acceptor substitutions in two-dimensional charge-transfer cumulene-containing aromatic molecules is analyzed. It is shown that a molecular design strategy proposed for one-dimensional charge-transfer molecules must be considerably altered for two-dimensional systems. It is found that the maximal two-photon cross section of such two-dimensional systems can often be well described by a four state model. The importance of the alignment of the transition dipole moments and of channel interference on the two-photon absorption cross sections is emphasized.

  • 40. Cronstrand, P.
    et al.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Time-dependent density-functional theory calculations of triplet-triplet absorption2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 22Article in journal (Refereed)
    Abstract [en]

    We present density-functional theory calculations of triplet-triplet absorption by three different approaches based on time-dependent density-functional theory (DFT): unrestricted DFT linear response, open-shell restricted DFT linear response applied to the triplet state, and quadratic response with triplet excitations applied to the ground state. Comparison is also made with corresponding results obtained by Hartree-Fock and multiconfiguration self-consistent-field response theory. Two main conclusions concerning triplet-triplet transitions are drawn in this study: First, the very good agreement between unrestricted and restricted DFT results indicates that spin contamination of the triplet state is not a serious problem when computing triplet-triplet spectra of common organic molecules. Second, DFT response calculations of triplet-triplet transitions can be affected by triplet instability problems, especially for the combination of DFT quadratic response with functionals containing fractional exact Hartree-Fock exchange.

  • 41.
    Cronstrand, Peter
    et al.
    KTH, Superseded Departments, Chemistry.
    Norman, P.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Few-states models for three-photon absorption2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 5, p. 2020-2029Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 43.
    Dalstein, Laetitia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. Univ Paris Saclay, Univ Paris Sud, CNRS, Lab Chim Phys, Batiment 201 P2, F-91405 Orsay, France.
    Revel, A.
    Univ Paris Saclay, Univ Paris Sud, CNRS, Lab Chim Phys, Batiment 201 P2, F-91405 Orsay, France.;CNRS, IN2P3, GANIL, CEA,DSM, Blvd Henri Becquerel, F-14076 Caen, France..
    Humbert, C.
    Univ Paris Saclay, Univ Paris Sud, CNRS, Lab Chim Phys, Batiment 201 P2, F-91405 Orsay, France..
    Busson, B.
    Univ Paris Saclay, Univ Paris Sud, CNRS, Lab Chim Phys, Batiment 201 P2, F-91405 Orsay, France..
    Nonlinear optical response of a gold surface in the visible range: A study by two-color sum-frequency generation spectroscopy. I. Experimental determination2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 13, article id 134701Article in journal (Refereed)
    Abstract [en]

    We experimentally determine the effective nonlinear second-order susceptibility of gold over the visible spectral range. To reach that goal, we probe by vibrational two-color sum-frequency generation spectroscopy the methyl stretching region of a dodecanethiol self-assembled monolayer adsorbed on a gold film. The sum-frequency generation spectra show a remarkable shape reversal when the visible probe wavelength is tuned from 435 to 705 nm. After correcting from Fresnel effects, the methyl stretching vibrations serve as an internal reference, allowing to extract the dispersion of the absolute phase and relative amplitude of the effective nonlinear optical response of gold in the visible range.

  • 44.
    Davis, Sergio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belonoshko, Anatoly
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, Natalia
    van Duin, Adri
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    High-pressure melting curve of hydrogen2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, p. 194508-Article in journal (Refereed)
    Abstract [en]

    The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates considerably from density functional theory calculations. Due to this, the computed melting curve, although shares most of the known features, yields considerably lower melting temperatures compared to extrapolations of the available diamond anvil cell data. This failure of the ReaxFF model, which can reproduce many physical and chemical properties (including chemical reactions in hydrocarbons) of solid hydrogen, hints at an important change in the mechanism of interaction of hydrogen molecules in the liquid state.

  • 45. Deng, Yunfeng
    et al.
    Gao, Bin
    Deng, Mingsen
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    A comparative theoretical study on core-hole excitation spectra of azafullerene and its derivatives2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 12, p. 124304-Article in journal (Refereed)
    Abstract [en]

    The core-hole excitation spectra-near-edge x-ray absorption spectroscopy (NEXAFS), x-ray emission spectroscopy (XES), and x-ray photoelectron spectroscopy (XPS) shake-up satellites have been simulated at the level of density functional theory for the azafullerene C59N and its derivatives (C59N)(+), C59HN, (C59N)(2), and C59N-C-60, in which the XPS shake-up satellites were simulated using our developed equivalent core hole Kohn-Sham(ECH-KS) density functional theory approach [B. Gao, Z. Wu, and Y. Luo, J. Chem. Phys. 128, 234704 (2008)] which aims for the study of XPS shake-up satellites of large-scale molecules. Our calculated spectra are generally in good agreement with available experimental results that validates the use of the ECH-KS method in the present work. The nitrogen K-edge NEXAFS, XES, and XPS shake-up satellites spectra in general can be used as fingerprints to distinguish the azafullerene C59N and its different derivatives. Meanwhile, different carbon K-edge spectra could also provide detailed information of (local) electronic structures of different molecules. In particular, a peak (at around 284.5 eV) in the carbon K-edge NEXAFS spectrum of the heterodimer C59N-C-60 is confirmed to be related to the electron transfer from the C59N part to the C-60 part in this charge-transfer complex.

  • 46.
    Duan, Sai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Guangjun
    Xie, Zhen
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Gauge invariant theory for super high resolution Raman images2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 19, article id 194106Article in journal (Refereed)
    Abstract [en]

    The use of a highly localized plasmonic field has enabled us to achieve sub-nanometer resolution of Raman images for single molecules. The inhomogeneous spatial distribution of plasmonic field has become an important factor that controls the interaction between the light and the molecule. We present here a gauge invariant interaction Hamiltonian (GIIH) to take into account the nonuniformity of the electromagnetic field distribution in the non-relativistic regime. The theory has been implemented for both resonant and nonresonant Raman processes within the sum-over-state framework. It removes the gauge origin dependence in the phenomenologically modified interaction Hamiltonian (PMIH) employed in previous studies. Our calculations show that, in most resonant cases, the Raman images from GIIH are similar to those from PMIH when the origin is set to the nuclear charge center of the molecule. In the case of nonresonant Raman images, distinct differences can be found from two different approaches, while GIIH calculations provide more details and phase information of the images. Furthermore, the results from GIIH calculations are more stable with respect to the computational parameters. Our results not only help to correctly simulate the resonant and nonresonant Raman images of single molecules but also lay the foundation for developing gauge invariant theory for other linear and nonlinear optical processes under the excitation of non-uniform electromagnetic field. Published by AIP Publishing.

  • 47.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Anisotropic self-diffusion in the nematic phase of a thermotropic liquid crystal by H-1-spin-echo nuclear magnetic resonance2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 4, p. 1946-1950Article in journal (Refereed)
    Abstract [en]

    The orientation-dependent molecular diffusion in the nematic liquid crystal 4-pentyl-4'-cyanobiphenyl is measured to high accuracy. The applied nuclear magnetic resonance method combines multiple-pulse homonuclear dipolar decoupling with pulsed-field-gradient stimulated echo and slice selection. The obtained temperature dependencies of the principal diffusion coefficients are not described by a simple Arrhenius relationship but reflect the decrease of the molecular orientational order close to the nematic-to-isotropic phase transition. The geometric average of the principal diffusion coefficients is continuous with the diffusion coefficient in the isotropic phase. The results are best described in terms of the affine transformation model of diffusion in hard-ellipsoid nematics.

  • 48. Dvinskikh, Sergey V.
    et al.
    Sandstrom, D.
    Luz, Z.
    Zimmermann, H.
    Maliniak, A.
    Molecular structure and order of hexaoctyloxy-rufigallol in the solid and columnar phases: Analysis of H-2-C-13 dipolar and C-13 chemical-shift interactions2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 1, p. 413-422Article in journal (Refereed)
    Abstract [en]

    We report a C-13 NMR investigation of 1,2,3,5,6,7-hexaoctyloxy-rufigallol in the solid and columnar phases using various H-2- and C-13-labeled isotopomers. The measurements were performed under both static and magic-angle spinning conditions. The conformations of the aliphatic side chains were derived from an analysis of H-2-C-13 dipolar and C-13 chemical-shift interactions. The nonequivalent chains exhibit significantly different structural behavior in both solid and columnar phase. It emerged that one of the side chains adopts an in-plane structure, while the other two chains prefer antiparallel out-of-plane conformations. Quantum-chemical calculations of the C-13 chemical-shift tensors were also carried out. These calculations support the experimental findings.

  • 49. Dvinskikh, Sergey V.
    et al.
    Yamamoto, Kazutoshi
    Ramamoorthy, Ayyalusamy
    Heteronuclear isotropic mixing separated local field NMR spectroscopy2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 3Article in journal (Refereed)
    Abstract [en]

    This paper presents a theoretical, numerical, and experimental study of a new class of separated local field (SLF) techniques. These techniques are based on the heteronuclear isotropic mixing leading to spin exchange via the local field (HIMSELF). It is shown that highly efficient and robust SLF experiments can be designed based on double channel windowless homonuclear decoupling sequences. Compared to rotating frame techniques based on Hartmann-Hahn cross polarization, the new approach is less susceptible to the frequency offset and chemical shift interaction and can be applied in the structural studies of macromolecules that are uniformly labeled with isotopes such as C-13 and N-15. Furthermore, isotropic mixing sequences allow for transfer of any magnetization component of one nucleus to the corresponding component of its dipolar coupled partner. The performance of HIMSELF is studied by analysis of the average Hamiltonian and numerical simulation and is experimentally demonstrated on a single crystalline sample of a dipeptide and a liquid crystalline sample exhibiting motionally averaged dipolar couplings.

  • 50. Dvinskikh, Sergey V.
    et al.
    Zimmermann, H.
    Maliniak, A.
    Sandstrom, D.
    Heteronuclear dipolar recoupling in solid-state nuclear magnetic resonance by amplitude-, phase-, and frequency-modulated Lee-Goldburg cross-polarization2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 4Article in journal (Refereed)
    Abstract [en]

    This paper presents a theoretical, numerical, and experimental study of phase- and frequency-switched Lee-Goldburg cross-polarization (FSLG-CP) under magic-angle spinning conditions. It is shown that a well-defined amplitude modulation of one of the two radio-frequency (rf) fields in the FSLG-CP sequence results in highly efficient heteronuclear dipolar recoupling. The recoupled dipolar interaction is gamma-encoded and, under ideal conditions, the effective spin Hamiltonian is equivalent to that in continuous-wave Lee-Goldburg CP. In practice, however, FSLG-CP is less susceptible to rf field mismatch and inhomogeneity, and provides better suppression of H-1 spin diffusion. The performance of FSLG-CP is experimentally demonstrated on liquid-crystalline samples exhibiting motionally averaged dipolar couplings.

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