Digitala Vetenskapliga Arkivet

Change search
Refine search result
12345 101 - 150 of 201
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Malmqvist, Per-Åke
    Björn’s top ten2003In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 110, no 3, p. 115-117Article in journal (Other academic)
  • 102.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Olsen, Jeppe
    Roos, Björn O
    Low-rank configuration interaction with orbital optimization - the LR SCF approach1988In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 148, no 4, p. 276-280Article in journal (Refereed)
    Abstract [en]

    Orbital optimization has been included in the low-range (LR) CI approach to configuration interaction, It is shown to have a noticeable effect on the computed correlation energy when only a small number of single excitation operators are used to approximate the doubly excited part of the wavefunction. The importance of optimization decreases rapidly when the number of parameters describing the LR wavefunction is increased. Test calculations are performed for H2O (geometry optimization) and for the polarizability of F. Optimization of the orbitals leads to improved convergence for all properties studied.

  • 103. Lindh, Roland
    et al.
    Pedersen, Thomas B.
    Aquilante, Francesco
    PHYS 142-Cholesky decomposition in computational chemistry2008Conference paper (Other academic)
  • 104.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Pedersen, Thomas B
    Aquilante, Francesco
    PHYS 142-Cholesky decomposition in computational chemistry2008Conference paper (Other academic)
  • 105.
    Lindh, Roland
    et al.
    Department of Chemistry and Biochemistry, University of California.
    Pegg, Ian L
    Knobler, Charles M
    Sscott, Robert L
    Approaches to the Tricritical Point in Quasibinary Fluid Mixtures1984In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 52, no 10, p. 839-842Article in journal (Refereed)
    Abstract [en]

    When the Griffiths theory of tricritical points is extended to the eighth power of the order parameter, certain composition differences preserve the limiting behavior far from the tricritical point, an unexpected result that had been overlooked in earlier van der Waals model calculations. New calculations show that, along a path of constant tricritical composition and density and increasing temperature, a quasibinary system goes from two phases to one at the tricritical point, with no appearance of the third phase.

  • 106.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Persson, B Joakim
    Ab Initio Study of the Bergman Reaction: The Autoaromatization of Hex-3-ene-1,5-diyne1994In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 116, no 11, p. 4963-4969Article in journal (Refereed)
    Abstract [en]

    The Bergman reaction of the hex-3-ene-1,5-diyne molecule (enediyne) to form the singlet biradical p-benzyne structure under ring closure has been studied by ab initio methods. The complete active space (CAS) SCF method was used for geometry optimizations at five points along the reaction path of the Bergman reaction. Subsequent calculations using the multireference second-order perturbation theory based on a CASSCF reference (CASPT2) established the energetics along the reaction path, especially for the reactant, transition state, and product. The energetics were further corrected for zero point vibrational energy at the CASSCF level of theory. The study incorporated four different basis sets: a double-zeta plus polarization (DZP), a triple-zeta plus double polarization (TZ2P), and two different average atomic natural orbital (ANO) basis sets. The study predicts the energy barrier to ring closure to be 25.0 +/- 3.1 kcal/mol and the enthalpy of reaction to be 4.9 +/- 3.2 kcal/mol. The latter value deviates significantly from the value estimated on the basis of group additivity and the Born-Haber cycle. The enediyne moiety is the main functional group of a new class of anticancer agents. The activation of the Bergman reaction in these drugs has been argued to be due to a small structural change in the terminal-terminal carbon distance of about -0.5 Angstrom originating from an epoxide conversion in the rest of the drug. The present study indicates that such a structural change is not sufficient for the Bergman autoaromatization to proceed at an appreciable rate. A new reaction path involving no biradical formation, resulting in the same products, is suggested.

  • 107.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Rice, Julia E
    Lee, Timothy J
    The energy separation between the classical and nonclassical isomers of protonated acetylene: An extensive study in one‐ and n‐particle space1991In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 94, no 12, p. 8008-8014Article in journal (Refereed)
    Abstract [en]

    The energy separation between the classical and nonclassical forms of protonated acetylene has been reinvestigated in light of the recent experimentally deduced lower bound to this value of 6.0 kcal/mol. The objective of the present study is to use state-of-the-art ab initio quantum mechanical methods to establish this energy difference to within chemical accuracy (i.e., about 1 kcal/mol). The one-particle basis sets include up to g-type functions and the electron correlation methods include single and double excitation coupled-cluster (CCSD), the CCSD(T) extension, multireference configuration interaction, and the averaged coupled-pair functional methods. A correction for zero-point vibrational energies has also been included, yielding a best estimate for the energy difference between the classical and nonclassical forms of 3.7 +/- 1.3 kcal/mol.

  • 108.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Roos, Björn O
    A theoretical study of the diffuseness of the V(1B1u) state of planar ethylene1989In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 35, no 6, p. 813-825Article in journal (Refereed)
    Abstract [en]

    The ground (N) state and the 1B1u(V) excited state of planar ethylene have been studied at the CPF and MR-SDCI levels of theory, using an extended CGTO basis set of the ANO type. The investigation especially addresses the near-degeneracy problem in the ground state and the coupling between the diffuse character of the π* orbital and the amount of correlation included in the wave function of the V state. The MR-SDCI results yield a vertical excitation energy in the range 7.8–8.0 eV, whereas the CPF result is 7.9 eV. The best MR-SDCI result for 〈1π*‖z2‖1π*〉 is 7.8, whereas CPF calculations based on MR-SDCI INOS give the value 6.7. It is clear from the results that these numbers have not converged and that more extended calculations than was possible in the present work would yield an even more compact wave function.

  • 109.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Roos, Björn O
    Jonsäll, Göran
    Ahlberg, Per
    A MCSCF study of homoaromaticity and the role of ion pairing in the stabilization of carbanions1986In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 108, no 21, p. 6554-6561Article in journal (Refereed)
    Abstract [en]

    The bicyclo[3.2.1]octa-3,6-dien-2-yl anion (I), the anion I lithium cation complex, the allyl anion (X), the allylradical, the allyl anion lithium cation complex, the ethene molecule, and the ethene lithium cation complex have been studiedby means of multiconfigurational SCF (MCSCF) and analytical gradients. The calculations have been confined to minimaland split-valence basis sets. The large distance between the C2 olefinic bridge and the C3 carbanionic bridge of anion I andthe short C6-C7 bond distance imply bishomoaromaticity to be negligible. According to these results, homoaromaticity isnot responsible for the observed stability in many potentially homoaromatic carbanions. The stability of anion I in the gasphase is instead explained in terms of a simple electrostatic model, where the quadrupole moment in the C2 olefinic bridgestabilizes the charge in the C, carbanionic bridge. This model agrees quantitatively with experiment. Calculations on theanion I lithium cation complex showed that in solution an additional attractive interaction between the C2 olefinic bridge andthe lithium cation can contribute. This additional interaction is estimated to stabilize the carbanion-lithium ion pair in thegas phase by about 16 kcal/mol. However, the stabilizing interactions of anion I in solution (quadrupole-charge andcounterion-anion interactions) will be reduced by solvent shielding. The relative ratios of the different stabilizing interactionsare therefore difficult to estimate. The geometrical findings of this paper have been verified by a recent X-ray experiment.

  • 110.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Roos, Björn O
    Kraemer, Wolfgang P
    A CAS SCF CI study of the hydrogen migration potential in protonated acetylene, C2H3+1987In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 139, no 5, p. 407-416Article in journal (Refereed)
    Abstract [en]

    CAS SCF CI studies have been performed on the protonated acetylene molecule, using extended Gaussian basis sets (C/5s, 4p,2d, lf/H/3s, 2p) of the general contraction type. Full geometry optimization has been performed for the classical and non-classicalstructures, and along a planar rearrangement path between these two structures. The non-classical bridged structure is found tobe about 4 kcahmol more stable than the classical one. A small barrier ( < 1 kcallmol ) is predicted along the rearrangement path.The proton affinity of acetylene has been calculated to have a value of 154.8 kcallmol, in good agreement with the experimentalestimate of 153.3 kcabmol. The rotationai constant for rotation around the CC bond has been determined to be 13.42 cm- ‘. Thestretching frequency for the bridging proton perpendicular to the CC bond was found to be 2100 cm-‘.

  • 111.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Ryde, Ulf
    Schütz, Martin
    On the significance of the trigger reaction in the action of the calicheamicin gamma(I)(1) anti-cancer drug1997In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 97, no 1-4, p. 203-210Article in journal (Refereed)
    Abstract [en]

    The significance of the so-called trigger reaction in the reaction mechanism of the calicheamicin gamma(1)(l) anti-cancer drug has been studied with ab initio quantum chemical methods. The structures of four fragments of calicheamicin gamma(1)(l), consisting of either 39 or 41 atoms, have been fully optimized using the Becke-Perdew86 density functional method and the 6-31G* basis sets. The four structures constitute members of an isodesmic for which the reaction energy is a direct of the change in activation energy of the Bergman reaction, caused by the structural rearrangements of the preceding trigger reaction. This difference in activation energy has been calculated with density functional theory, using the exchange-correlation functional mentioned above, and with second-order Moller-Plesset perturbation theory (MP2), employing an ANO-type basis set. In both cases a value of 12 kcal/mol is obtained. The study firmly supports the hypothesis that the significance of the trigger reaction is to saturate a double bond in the vicinity of the enediyne group, which counteracts the formation of the biradical state of the drug. The MP2 computations became feasible by a novel implementation of an integral-direct, distributed-data, parallel MP2 algorithm.

  • 112. Lindh, Roland
    et al.
    Ryu, U
    Liu, B
    The reduced multiplication scheme of the Rys quadrature and new recurrence relations for auxiliary function based two‐electron integral evaluation1991In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 95, no 8, p. 5889-5897Article in journal (Refereed)
    Abstract [en]

    The reduced multiplication scheme of the Rys quadrature is presented. The method is based on new ways in which the Rys quadrature can be developed if it is implemented together with the transfer equation applied to the contracted integrals. In parallel to the new scheme of the Rys quadrature improvements are suggested to the auxiliary function based algorithms. The two new methods have very favorable theoretical floating point operation (FLOP) counts as compared to other methods. It is noted that the only significant difference in performance of the two new methods is due to the vectorizability of the presented algorithms. In order to exhibit this, both methods were implemented in the integral program SEWARD. Timings are presented for comparisons with other implementations. Finally, it is demonstrated how the transfer equation in connection with the use of spherical harmonic Gaussians offers a very attractive path to compute the two-electron integrals of such basis functions. It is demonstrated both theoretically and with actual performance that the use of spherical harmonic Gaussians offers a clear advantage over the traditional evaluation of the two-electron integrals in the Cartesian Gaussian basis.

  • 113.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Schütz, Martin
    Singlet benzyne thermochemistry: A CASPT2 study of the enthalpies of formation1996In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 258, no 3-4, p. 409-415Article in journal (Refereed)
    Abstract [en]

    The enthalpies of formation for singlet benzynes were examined at the CASPT2 (second order perturbation theory, based on a complete active space SCF reference function) level of theory, The study employed isodesmic reactions in order to minimize the influence of systematic errors of the method. The results obtained for m- and p-benzyne were found to dispute earlier experimentally deduced values; a discrepancy of about 5 kcal/mol was observed. As a consequence, the enthalpy of reaction of the so called Bergman reaction, deduced previously from the experimental enthalpy of formation of p-benzyne, seems to be overestimated by about 5 kcal/mol. Furthermore, it was observed that the CCSD(T) method (coupled cluster singles and doubles with a perturbatative estimate of the triples contribution) is inappropriate for a balanced treatment of the Bergman reaction, due to the extensive differences in the electronic structures of the two reactants.

  • 114.
    Lindh, Roland
    et al.
    Department of Theoretical Chemistry, Lund University.
    Wisborg Krogh, Jesper
    Schütz, Martin
    Hirao, Kimihiko
    Semidirect parallel self-consistent field: the load balancing problem in the input/output intensive self-consistent field iterations2003In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 110, no 3, p. 156-164Article in journal (Refereed)
    Abstract [en]

    The full capacity of contemporary parallel computers can, in the context of iterative ab initio procedures like, for example, self-consistent field (SCF) and multiconfigurational SCF, only be utilized if the disk and input/output (I/O) capacity are fully exploited before the implementation turns to an integral direct strategy. In a recent report on parallel semidirect SCF http://www.tc.cornell.edu/er/media/1996/collabrate.html, http://www.fp.mcs.anl.gd/grand-challenges/chem/non-direct/index.html it was demonstrated that super-linear speedups are achievable for algorithms that exploit scalable parallel I/O. In the I/O-intensive SCF iterations of this implementation a static load balancing, however, was employed, dictated by the initial iteration in which integral evaluation dominates the central processing unit activity and thus determines the load balancing. In the present paper we present the first implementation in which load balancing is achieved throughout the whole SCF procedure, i.e. also in subsequent iterations. The improved scalability of our new algorithm is demonstrated in some test calculations, for example, for 63-node calculation a speedup of 104 was observed in the computation of the two-electron integral contribution to the Fock matrix.

  • 115. Liu, Fengyi
    et al.
    Liu, Yajun
    De Vico, Luca
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    A CASSCF/CASPT2 approach to the decomposition of thiazole-substituted dioxetanone: Substitution effects and charge-transfer induced electron excitation2009In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 484, no 1-3, p. 69-75Article in journal (Refereed)
    Abstract [en]

    The gas-phase decompositions of a thiazole-substituted dioxetanone, in both the natural and anionic forms, were investigated theoretically in a CASSCF/CASPT2 study. The neutral conjugated thiazole (with or without a hydroxyl group) substitution on the dioxetanone has no evident effect on the dissociation; however, a subsequent deprotonation - invoking charge-transfer excitations from the thiazole to the dioxetanone moiety - will dramatically change the reaction mechanism from stepwise to concerted, and reduce the activation barrier by similar to 8 kcal mol(-1). These findings are helpful for the better understanding of dioxetanone chemiluminescence and the charge-transfer induced electron excitation in chemi- and bioluminescence processes.

  • 116. Liu, Fengyi
    et al.
    Liu, Yajun
    De Vico, Luca
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Theoretical Study of the Chemiluminescent Decomposition of Dioxetanone2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 17, p. 6181-6188Article in journal (Refereed)
    Abstract [en]

    The unimolecular chemiluminescent decomposition of unsubstituted dioxetanone was studied at the complete active space self-consistent field level of theory combined with the multistate second-order multiconfigurational perturbation theory energy correction. The calculations revealed interesting features. Two transition states, two conical intersections, and one intermediate stable biradical structure along the lowest energy reaction path were identified. It was noted that the conical intersections are found at or in very close proximity to the transition states. The first and second transition states correspond to O-O and C-C cleavages, respectively. In particular, a planar structure is supported by the(1)(sigma,sigma*) state during the O-O dissociation up to the first transition state and conical intersection. At this point the (1)(sigma,sigma*) state dissociation path bifurcates, corresponding to a torsion of the O-C-C-O angle. Simultaneously, the (1)(n,sigma*) state becomes lower in energy while still favoring a planar structure. As the lowest-energy reaction path proceeds toward the second transition state and conical intersection, the (1)(n,sigma*), (3)(n,sigma*), and (1)(sigma,sigma*)states are close in energy. This work suggests that the vibrational distribution at the first conical intersection and the interactions among the states as the reaction proceeds between the two transition states are the origin of the population of the chemiluminescent (n,sigma*) states.

  • 117. Liu, Y J
    et al.
    Ajitha, D
    Krogh, J W
    Tarnovsky, A N
    Lindh, Roland
    Department of Chemical Physics, Chemical Center, Lund University.
    Spin-orbit ab initio investigation of the photolysis of bromoiodomethane2006In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 7, no 4, p. 955-963Article in journal (Refereed)
    Abstract [en]

    The photodissociation of bromoiodomethane has been investigated by spin-orbit ab initio calculations. The experimentally observed A- and B-bands and the corresponding photoproducts were assigned by multistate second-order multiconfigurationol perturbation theory in conjunction with spin-orbit interaction through complete active space state interaction potential energy curves, vertical excitation energies, and oscillator strengths of low-lying excited states. The present conclusions with respect to the dissociation process in the B-band are different compared with those of previous studies. The reaction between the iso-CH2,Br-I and iso-CH2I-Br species has also been studied. Finally, a set of stable excited states was identified for both isomers. These species might be of importance in the recombination process that follows the photodissociotion in a solvent.

  • 118. Liu, Ya-Jun
    et al.
    De Vico, Luca
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Ab initio investigation on the chemical origin of the firefly bioluminescence2008In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 194, no 2-3, p. 261-267Article in journal (Refereed)
    Abstract [en]

    The chemical origin of the firefly bioluminescence has been investigated by means of density functional and multireference theoretical methods. Different hypotheses on the mechanism of multicolour emission have been investigated: twisting around the central carbon-carbon bond, polarizability of the oxyluciferin microenvironment and presence of resonance structures. The calculated results indicated that the higher the polarizability of the microenvironment is, the larger the red shift of the bioluminescence is. Moreover, a quite flat potential energy surface should allow the easy shifting of the anion minimum between different pseudo-resonance structures. The possible effects of a tight or loose protein pocket has also been considered.

  • 119. Liu, Ya-Jun
    et al.
    De Vico, Luca
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Fang, Wei-Hai
    Spin-orbit ab initio investigation of the ultraviolet photolysis of diiodomethane2007In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 8, no 6, p. 890-898Article in journal (Refereed)
    Abstract [en]

    The UV photodissociation (<5 eV) of diiodomethane (CH(2)l(2)) is investigated by spin-orbit ab inito calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH(2)l(2) and CH(2)l-l lead to geminate-radical products, CH(2)l(+) +l(P-2(3/2)) or CH(2)l(+) + l*(P-2(1/2)). The recombination process from CH(2)l-l to CH(2)l(2) is explained by an isomerazation process and a secondary photodissociation reaction of CH(2)l-l. Finally, the study reveals that spin-orbits effects are sifnificant in the quantitative analysis of the electronic spectrum of the CH(2)l-l species.

  • 120. Liu, Ya-Jun
    et al.
    Roca-Sanjuan, Daniel
    Lindh, Roland
    Computational Photochemistry and Photophysics: the state of the art2012In: Photochemistry, The Royal Society of Chemistry , 2012, Vol. 40, p. 42-72Chapter in book (Other academic)
    Abstract [en]

    This review starts with the most basic concepts in photochemistry and photophysics, followed by a chronological introduction of theoretical methods and relevant applications in the history of computational photochemistry, along with the authors’ comments on the methodologies currently available for photochemical studies. Recent advances in the field are next summarized and discussed, focusing separately on methodology and computational techniques and some highlighted applied works carried out during the last two years on the topics of photodissociations, photostability, photodimerizations, photoisomerizations, proton/hydrogen transfer, photodecarboxylations, charge transport, bioexcimers, chemiluminescence and bioluminescence. We finish this review by conclusions and an outlook of the future.

  • 121. Malmquist, Per-Åke
    et al.
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Roos, Björn O
    Ross, Stephen
    An ab initio study of the molecular structure andvibration-rotation spectrum of the triplet radical HCCN1988In: THEORETICA CHIMICA ACTA, ISSN 0040-5744, Vol. 73, no 2-3, p. 155-171Article in journal (Refereed)
    Abstract [en]

    The bent triplet cyanocarbene H-C-CN and the linear triplet allene H-C=C=N have been studied by the CASSCF and CI methods, using a DZP basis. Relaxation of all geometrical parameters for the CASSCF energy results in a bent molecule with CCH angle 133° and a barrier to linearity of 6.4 kcal/mol, which was lowered to 2.3 kcal/mol in a subsequent CI calculation. The Davidson correction lowered it further to 1.8 kcal/mol.A 26-term analytical potential energy surface (PES) was fitted to CASSCF, CI, and Davidson corrected CI energies in 94 different geometries. Using these three potentials, the semi-rigid bender model predicts a CCH bending frequency of 782, 505, and 503 cm–1, resp., which compares favourably with an experimentally observed IR transition line at 458 cm–1. For the deuterated species, the corresponding frequencies are 610, 407, and 402 cm–1, to be compared with two possible absorption lines at 405 and 317.5 cm–1.The PES was then parametrized by adding a variable CCH angle dependence, and a comprehensive vibration-rotation spectrum was calculated variationally, using the exact 4-atom vibration-rotation kinetic Hamiltonian, for a range of barrier heights. Comparison with experiment indicates a barrier in the range 1±0.5 kcal/mol.

  • 122.
    Marazzi, Marco
    et al.
    Univ Lorraine Nancy, SRSMC, Theorie Modelisat Simulat, Blvd Aiguillettes, F-54000 Nancy, France.;Univ Vienna, Inst Theoret Chem, Wahringer Str 17, A-1090 Vienna, Austria..
    Mai, Sebastian
    CNRS, SRSMC, Theorie Modelisat Simulat, Blvd Aiguillettes, Nancy, France..
    Roca-Sanjuan, Daniel
    Univ Valencia, Inst Ciencia Mol, POB 22085, ES-46071 Valencia, Spain..
    Delcey, Mickael G.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Uppsala Univ, UC3, S-75105 Uppsala, Sweden..
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Uppsala Univ, UC3, S-75105 Uppsala, Sweden..
    Gonzalez, Leticia
    CNRS, SRSMC, Theorie Modelisat Simulat, Blvd Aiguillettes, Nancy, France..
    Monari, Antonio
    Univ Lorraine Nancy, SRSMC, Theorie Modelisat Simulat, Blvd Aiguillettes, F-54000 Nancy, France.;Univ Vienna, Inst Theoret Chem, Wahringer Str 17, A-1090 Vienna, Austria..
    Benzophenone Ultrafast Triplet Population: Revisiting the Kinetic Model by Surface-Hopping Dynamics2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 4, p. 622-626Article in journal (Refereed)
    Abstract [en]

    The photochemistry of benzophenone, a paradigmatic organic molecule for photosensitization, was investigated by means of surface-hopping ab initio molecular dynamics. Different mechanisms were found to be relevant within the first 600 fs after excitation; the long debated direct (S-1 -> T-1) and indirect (S-1 -> T-2 -> T-1) mechanisms for population of the low-lying triplet state are both possible, with the latter being prevalent. Moreover, we established the existence of a kinetic equilibrium between the two triplet states, never observed before. This fact implies that a significant fraction of the overall population resides in T-2, eventually allowing one to revisit the usual spectroscopic assignment proposed by transient absorption spectroscopy. This finding is of particular interest for photocatalysis as well as for DNA damages studies because both T-1 and T-2 channels are, in principle, available for benzophenone-mediated photoinduced energy transfer toward DNA.

    Download full text (pdf)
    fulltext
  • 123. Marazzi, Marco
    et al.
    Navizet, Isabelle
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theortical Chemistry.
    Frutos, Luis Manuel
    Photostability Mechanisms in Human gamma B-Crystallin: Role of the Tyrosine Corner Unveiled by Quantum Mechanics and Hybrid Quantum Mechanics/Molecular Mechanics Methodologies2012In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 4, p. 1351-1359Article in journal (Refereed)
    Abstract [en]

    The tyrosine corner is proposed as a featured element to enhance photostability in human gamma B-crystallin when exposed to UV irradiation. Different ultrafast processes were studied by multiconfigurational quantum chemistry coupled to molecular mechanics: photoinduced singlet singlet energy, electron and proton transfer, as well as population and evolution of triplet states. The minimum energy paths indicate two possible UV photoinduced events: forward backward proton-coupled electron transfer providing to the system a mechanism for ultrafast internal conversion, and energy transfer, leading to fluorescence or phosphorescence. The obtained results are in agreement with the available experimental data, being in line with the proposed photoinduced processes for the different tyrosine environments within gamma B-crystallin.

  • 124. Mastalerz, Remigius
    et al.
    Barone, Giampaolo
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Reiher, Markus
    Analytic high-order Douglas-Kroll-Hess electric field gradients2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 7, p. 074105-Article in journal (Refereed)
    Abstract [en]

    In this work we present a comprehensive study of analytical electric field gradients in hydrogen halides calculated within the high-order Douglas-Kroll-Hess (DKH) scalar-relativistic approach taking picture-change effects analytically into account. We demonstrate the technical feasibility and reliability of a high-order DKH unitary transformation for the property integrals. The convergence behavior of the DKH property expansion is discussed close to the basis set limit and conditions ensuring picture-change-corrected results are determined. Numerical results are presented, which show that the DKH property expansion converges rapidly toward the reference values provided by four-component methods. This shows that in closed-shell cases, the scalar-relativistic DKH(2,2) approach which is of second order in the external potential for both orbitals and property operator yields a remarkable accuracy. As a parameter-dependence-free high-order DKH model, we recommend DKH(4,3). Moreover, the effect of a finite-nucleus model, different parametrization schemes for the unitary matrices, and the reliability of standard basis sets are investigated.

  • 125. Mastalerz, Remigius
    et al.
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Reiher, Markus
    The Douglas-Kroll-Hess electron density at an atomic nucleus2008In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 465, no 1-3, p. 157-164Article in journal (Refereed)
    Abstract [en]

    The picture-change error on Douglas-Kroll-Hess (DKH) electron densities at atomic nuclei is analyzed in detail to high orders. Our results demonstrate that high-order DKH transformations of especially the property operator are needed to obtain converged results. However, if the convergence properties are discussed in terms of a relative error a fast convergence of the picture-change corrected DKH electron density at nuclei with the DKH order of orbitals and property operator is found. Furthermore, our results suggest that already the standard low-order DKH(2,2) model is likely to yield sufficiently accurate difference densities up to the third row of the periodic table.

  • 126. Mastalerz, Remigius
    et al.
    Widmark, Per-Olof
    Roos, Björn Olof
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Reiher, Markus
    Basis set representation of the electron density at an atomic nucleus2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 14, p. 144111-Article in journal (Refereed)
    Abstract [en]

    In this paper a detailed investigation of the basis set convergence for the calculation of relativistic electron densities at the position of finite-sized atomic nuclei is presented. The development of Gauss-type basis sets for such electron densities is reported and the effect of different contraction schemes is studied. Results are then presented for picture-change corrected calculations based on the Douglas-Kroll-Hess Hamiltonian. Moreover, the role of electron correlation, the effect of the numerical integration accuracy in density functional calculations, and the convergence with respect to the order of the Douglas-Kroll-Hess Hamiltonian and the picture-change-transformed property operator are studied.

  • 127. Melaccio, Federico
    et al.
    Olivucci, Massimo
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Ferré, Nicolas
    Unique QM/MM potential energy surface exploration using microiterations2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 13, p. 3339-3346Article in journal (Refereed)
    Abstract [en]

    The determination and the characterization of important points of a potential energy surface can be carried out routinely using any molecular modelling software based on either a quantum mechanical (QM) or a classical (molecular mechanics, MM) description of the particle interactions. However the coupling of the QM and MM descriptions (QM/MM) gives rise to severe efficiency limitations during a geometry optimization of the whole system, especially when both subsystems are coupled electrostatically. The present work introduces two simple improvements, mainly developed in the framework of the ElectroStatic Potential Fitted (ESPF) method to ensure the uniqueness of the QM/MM potential energy surface. The first one aims to improve the approximate Hessian matrix used in the QM optimization step. The second one tries to recouple electrostatically the QM and MM subsystems when microiterations are used. These methods are tested on a very simple system (a QM water molecule in a MM water box) before to be applied to the investigation of the light absorption in the rhodopsin protein at the multireference second-order perturbation level of theory (CASPT2). This work is dedicated to the memory of Prof. B. O. Roos. He was a great support for the implementation of the QM/MM method in the Molcas package.

  • 128. Merlot, Patrick
    et al.
    Kjaergaard, Thomas
    Helgaker, Trygve
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Aquilante, Francesco
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Reine, Simen
    Pedersen, Thomas Bondo
    Attractive electron-electron interactions within robust local fitting approximations2013In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 34, no 17, p. 1486-1496Article in journal (Refereed)
    Abstract [en]

    An analysis of Dunlap's robust fitting approach reveals that the resulting two-electron integral matrix is not manifestly positive semidefinite when local fitting domains or non-Coulomb fitting metrics are used. We present a highly local approximate method for evaluating four-center two-electron integrals based on the resolution-of-the-identity (RI) approximation and apply it to the construction of the Coulomb and exchange contributions to the Fock matrix. In this pair-atomic resolution-of-the-identity (PARI) approach, atomic-orbital (AO) products are expanded in auxiliary functions centered on the two atoms associated with each product. Numerical tests indicate that in 1% or less of all HartreeFock and KohnSham calculations, the indefinite integral matrix causes nonconvergence in the self-consistent-field iterations. In these cases, the two-electron contribution to the total energy becomes negative, meaning that the electronic interaction is effectively attractive, and the total energy is dramatically lower than that obtained with exact integrals. In the vast majority of our test cases, however, the indefiniteness does not interfere with convergence. The total energy accuracy is comparable to that of the standard Coulomb-metric RI method. The speed-up compared with conventional algorithms is similar to the RI method for Coulomb contributions; exchange contributions are accelerated by a factor of up to eight with a triple-zeta quality basis set. A positive semidefinite integral matrix is recovered within PARI by introducing local auxiliary basis functions spanning the full AO product space, as may be achieved by using Cholesky-decomposition techniques. Local completion, however, slows down the algorithm to a level comparable with or below conventional calculations. 

    Download full text (pdf)
    fulltext
  • 129. Moriarty, Niger W
    et al.
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Karlström, Gunnar
    Tetramethylene: A CASPT2 study1998In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 289, no 5-6, p. 442-450Article in journal (Refereed)
    Abstract [en]

    The potential energy surface (PES) of the 1,4-tetramethylene biradical has been reinvestigated at the complete-active-space self-consistent field (CASSCF), complete active space with second-order perturbation theory correction and multi-reference configuration interaction (MRCI) levels of theory. The choice of basis set, the size inconsistency of the MRCI wavefunction and the selection of the active space of the CASSCF wavefunction each have a considerable influence on the shape of the PES. In particular, the relative energy of the so-called GF and TF structures depends significantly on the level of theory employed. The results of the study suggest that the experimentally observed intermediate is more likely to be due to entropic trapping rather than the presence of a transition state.

  • 130. Nakayama, Kenichi
    et al.
    Hirao, Kimihiko
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Different bases for different correlation effects: multireference Moller-Plesset perturbation theory in the extended basis function space1999In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 300, no 3-4, p. 303-311Article in journal (Refereed)
    Abstract [en]

    A method to improve virtual orbitals of CASSCF theory has been proposed by expanding the virtual orbital space through the addition of basis functions without disturbing already established CASSCF function space. It is a natural extension of work used in Hartree-Fock calculations. The improved virtual orbitals are then used to estimate the dynamical correlation. That is, a moderate basis set is used in CASSCF to include nondynamical correlation and a sufficiently large basis set is used in multireference Moller-Plesset perturbation theory to estimate the slowly convergent dynamical correlation. The present formalism is tested on the barrier height of the H2CO –> H-2 + CO reaction, singlet-triplet energy separation in CH2 and valence pi-pi* excitation energies in butadiene. Numerical results show that good accuracy can be obtained.

  • 131. Navizet, Isabelle
    et al.
    Liu, Ya-Jun
    Ferre, Nicolas
    Chen, Shu-Feng
    Xiao, Hong-Yan
    Lindh, Roland
    Light emission in firefly: a theoretical study2012In: Luminescence (Chichester, England Print), ISSN 1522-7235, E-ISSN 1522-7243, Vol. 27Article in journal (Refereed)
  • 132. Navizet, Isabelle
    et al.
    Liu, Ya-Jun
    Ferre, Nicolas
    Chen, Shu-Feng
    Xiao, Hong-Yan
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Light emission in firefly: a theoretical study2012In: Luminescence (Chichester, England Print), ISSN 1522-7235, E-ISSN 1522-7243, Vol. 27, no 2, p. 146-146Article in journal (Other academic)
  • 133. Navizet, Isabelle
    et al.
    Liu, Ya-Jun
    Ferre, Nicolas
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Color-Modulation of firefly luciferin-luciferase system investigated by theoretical approach2010In: Abstracts of the 16th International Symposium on Bioluminescence and Chemiluminescence – (ISBC 2010): [Published in: Luminescence 2010; 25: 81–216], 2010, Vol. 25, no 2, p. 92-92Conference paper (Other academic)
  • 134. Navizet, Isabelle
    et al.
    Liu, Ya-Jun
    Ferre, Nicolas
    Roca Sanjuán, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Delcey, Mickaël
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    The chemistry of bioluminescence: an analysis of chemical functionalities2012In: Luminescence (Chichester, England Print), ISSN 1522-7235, E-ISSN 1522-7243, Vol. 27, no 2, p. 146-146Article in journal (Other academic)
  • 135. Navizet, Isabelle
    et al.
    Liu, Ya-Jun
    Ferre, Nicolas
    Roca Sanjuán, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Theoretical Chemistry.
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Theoretical Chemistry.
    The Chemistry of Bioluminescence: An Analysis of Chemical Functionalities2011In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, no 17, p. 3064-3076Article, review/survey (Refereed)
    Abstract [en]

    Firefly luciferase is one of the most studied bioluminescent systems, both theoretically and experimentally. Herein we review the current understanding of the bioluminescent process from a chemical functionality perspective based on those investigations. Three key components are emphasized: the chemiluminophore, the electron-donating fragment, and how these are affected by the substrateenzyme interaction. The understanding is based on details of how the peroxide ?O?O? bond supports the production of electronically excited products and how the charge-transfer (CT) mechanism, with the aid of an electron-donating group, lowers the activation barrier to support a reaction occurs in living organisms. For the substrateenzyme complex it is demonstrated that the enzyme can affect the hydrogen-bonding around the CT-controlling group, resulting in a mechanism for color modulation. Finally, we analyse other luciferinluciferase systems and compare them to the key chemical functionalities of the fragments of the luciferinluciferase complex with respect to similarities and differences.

  • 136. Navizet, Isabelle
    et al.
    Liu, Ya-Jun
    Ferré, Nicolas
    Xiao, Hong-Yan
    Fang, Wei-Hai
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Color-Tuning Mechanism of Firefly Investigated by Multi-Configurational Perturbation Method2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 2, p. 706-712Article in journal (Refereed)
    Abstract [en]

    This is the first report on a multiconfigurational reference second-order perturbation theory−molecular mechanics study of the color modulation of the observed bioluminescence of the oxyluciferin−luciferase complex of the Japanese genji-botaru firefly using structures according to recent X-ray data. Our theoretical results do not support the experimentally deduced conclusion that the color modulation of the emitted light primarily depends on the size of the compact luciferase protein cavity embedding the excited oxyluciferin molecule. Rather, we find, in agreement with recent experimental observations, that the wavelength of the emitted light depends on the polarity of the microenvironment at the phenol/phenolate terminal of the benzothiazole fragment in oxyluciferin.

  • 137. Navizet, Isabelle
    et al.
    Roca-Sanjuán, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Yue, Ling
    Liu, Ya-Jun
    Ferré, Nicolas
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Are the Bio- and Chemiluminescence States of the Firefly Oxyluciferin the Same as the Fluorescence State?2013In: Photochemistry and Photobiology, ISSN 0031-8655, E-ISSN 1751-1097, Vol. 89, no 2, p. 319-325Article in journal (Refereed)
    Abstract [en]

    A usual strategy in both experimental and theoretical studies on bio- and chemiluminescence is to analyze the fluorescent properties of the bio- and chemiluminescence reaction product. Recent findings in a coelenteramide and Cypridina oxyluciferin model arise a concern on the validity of this procedure, showing that the light emitters in each of these luminescent processes might differ. Here, the thermal decomposition path of the firefly dioxetanone and the light emission states of the Firefly oxyluciferin responsible for the bio-, chemiluminescence, and fluorescence of the molecule are characterized using ab initio quantum chemistry and hybrid quantum chemistry/molecular mechanics methods to determine if the scenario found in the coelenteramide and Cypridina oxyluciferin study does also apply to the Firefly bioluminescent systems. The results point out to a unique emission state in the bio-, chemiluminescence, and fluorescence phenomena of the Firefly oxyluciferin and, therefore, using fluorescence properties of this system is reasonable.

  • 138. Olsen, Jeppe
    et al.
    Malmqvist, Per-Åke
    Roos, Björn O
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Widmark, Per-Olof
    A non-linear approach to configuration interaction: The low-rank CI method (LR CI)1987In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 133, no 2, p. 91-101Article in journal (Refereed)
    Abstract [en]

    An alternative to the linear CI expansion is presented, which is based on the spectral resolution of the double excitation CI coefficients arranged as a symmetric matrix. The resulting energy expression is a quartic function of the new variables, where the double excitation operator is given as 2 = ∑IMωI(I)2, where d̂dI is a single excitation operator: I =∑Ia,IiaÊai. Since M is a small number, the number of variables is reduced considerably compared to normal SDCI, with only little loss in accuracy. A program for non-linear CI calculations has been written and is presented with results for H2O and N2. The method can easily be extended to include orbital optimization and cluster terms in the wavefunction, still yielding a fully variational approximation to the Schrödinger equation.

  • 139. Paulovic, Jozef
    et al.
    Nakajima, Takahito
    Hirao, Kimihiko
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Malmqvist, Per Åke
    Relativistic and correlated calculations on the ground and excited states of ThO2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 2, p. 798-805Article in journal (Refereed)
    Abstract [en]

    We report on the performance of the third-order Douglas-Kroll ab initio model potential (DK3-AIMP) method-based electron-correlated spin-orbit calculations. Our treatment assumes that the problem can be separated into a spin-free correlation treatment and a spin-orbit calculation. The correlation effects were calculated using the multistate complete active space second-order perturbation method, and the spin-orbit effects were treated by means of the restricted active space state interaction spin-orbit method, where the spin-orbit effects were approximated by the Douglas-Kroll type of atomic mean-field spin-orbit method. We used our method for illustrative calculations on the ground and low-lying electronic states of thorium monoxide. For a proper description of the inner core region in the spin-orbit calculations, an auxiliary spin-orbit basis set was introduced. The DK3-AIMP-based electron-correlated spin-orbit calculations on ThO yield good agreement with corresponding all-electron results and with the available experimental data. This confirms that the DK3-AIMP method can be easily combined with highly accurate correlation treatments and relativistic effects, both of which are vital for studying the actinides. To our knowledge, the literature contains no references to AIMP calculations on the low-lying states of ThO.

  • 140. Pedersen, Thomas Bondo
    et al.
    Aquilante, Francesco
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Density fitting with auxiliary basis sets from Cholesky decompositions2009In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 124, no 1-2, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Recent progress in the use of Cholesky decomposition techniques within the density fitting approximation of two-electron integrals is reviewed with emphasis on the theoretical background. Special attention is paid to the fact that errors due to the density fitting approximation can be controlled by constructing auxiliary basis sets by means of Cholesky decomposition of either the entire or certain subblocks of the molecular two-electron integral matrix. Finally, the prospects of trivial linear-scaling calculation of fitting coefficients in the Cholesky decomposition-based density fitting scheme are outlined.

  • 141. Persson, Petter
    et al.
    Brinck, Tore
    Lindh, Roland
    Introduction2012In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 112, no 7, p. 1759-1759Article in journal (Refereed)
  • 142. Raab, Juraj
    et al.
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Wang, Xuefeng
    Andrews, Lester
    Gagliardi, Laura
    A combined experimental and theoretical study of uranium polyhydrides with new evidence for the large complex UH4(H-2)(6)2007In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 28, p. 6383-6387Article in journal (Refereed)
    Abstract [en]

    Several monouranium and diuranium polyhydride molecules were investigated using quantum chemical methods. The infrared spectra of uranium and hydrogen reaction products in condensed neon and pure hydrogen were measured and compared with previous argon matrix frequencies. The calculated molecular structures and vibrational frequencies were used to identify the species present in the matrix. Major new absorptions were observed and compared with the previous argon matrix study. Spectroscopic evidence was obtained for the novel complex, UH4(H-2)(6), which has potential interest as a metal hydride with a large number of hydrogen atoms bound to uranium. Our calculations show that the series of complexes UH4(H-2)(1,2,4,6) are stable.

  • 143. Rasmusson, M
    et al.
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Lascoux, N
    Tarnovsky, A N
    Kadi, M
    Kuhn, O
    Sundström, V
    Åkesson, E
    Photodissociation of bromobenzene in solution2003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 367, no 5-6, p. 759-766Article in journal (Refereed)
    Abstract [en]

    The photodissociation of bromobenzene in solution was investigated with ultrafast transient absorption spectroscopy following excitation at 266 nm. Ab initio calculations of lower singlet and triplet states were performed in order to guide the interpretations. The main feature of the kinetics measured between 300 and 930 nm in acetonitrile is a 9 +/- 1ps decay, which we mainly assign to predissociation. Similar decays were observed in hexane, dichloromethane and tetrachloromethane at 400 and 800 nm. Other features in acetonitrile, such as complicated short-time dynamics between 420 and 620 nm and a long-lived component, might indicate the involvement of lower triplet states.

  • 144.
    Reine, Simen
    et al.
    Dept. of Chemistry, Oslo University, Oslo, Norway.
    Helgaker, Trygve
    Dept. of Chemistry, Oslo University, Oslo, Norway.
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theortical Chemistry.
    Multi-electron Integrals2012In: Wiley Interdisciplinary Reviews: Computational Molecular Science, ISSN 1759-0884, Vol. 2, no 2, p. 290-303Article, review/survey (Refereed)
    Abstract [en]

    This review presents techniques for the computation of multi-electron integrals over Cartesian and solid-harmonic Gaussian-type orbitals as used in standard electronic-structure investigations. The review goes through the basics for one- and two-electron integrals, discuss details of various two-electron integral evaluation schemes, approximative methods, techniques to compute multi-electron integrals for explicitly correlated methods, and property integrals.

  • 145. Rendell, Alistair P
    et al.
    Lee, Timothy J
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Quantum chemistry on parallel computer architectures: oupled-cluster theory applied to the bending potential of fulminic acid1992In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 194, no 1-2, p. 84-94Article in journal (Refereed)
    Abstract [en]

    We present a formulation of the singles and doubles coupled-cluster (CCSD) method suitable for distributed memory parallel computer architectures. Results from test calculations using up to 128 nodes of the Intel i860 hypercube are presented. Although the new algorithm is highly parallel, the asymptotic speed is quickly reached due to the input/output (IO) demands on the concurrent file system. To alleviate these IO problems, as well as disk storage requirements, we propose a “semi-direct” CCSD method whereby the atomic orbital integrals are evaluated in each iteration of the procedure in order to determine the contribution from certain terms. Using CCSD(T)/TZ2P optimized geometries, the calculations show that the Born-Oppenheimer ground-state potential energy surface yields a linear structure for fulminic acid. HCNO, in agreement with the semirigid bender analysis by Bunker, Landsberg and Winnewisser.

  • 146. Robb, Mike
    et al.
    Siegbahn, Per
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Foreword: Special Issue, A Celebration of the Scientific Achievements of Bjorn O. Roos2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 13, p. 3255-3255Article in journal (Refereed)
  • 147.
    Roca Sanjuán, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Delcey, Mickaël G.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Navizet, Isabelle
    Ferre, Nicolas
    Liu, Ya-Jun
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    WARNING: The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!2012In: Luminescence (Chichester, England Print), ISSN 1522-7235, E-ISSN 1522-7243, Vol. 27, no 2, p. 155-156Article in journal (Other academic)
  • 148.
    Roca-Sanjuan, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Aquilante, Francesco
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Multiconfiguration second-order perturbation theory approach to strong electron correlation in chemistry and photochemistry2012In: Wiley Interdisciplinary Reviews: Computational Molecular Science, ISSN 1759-0876, Vol. 2, no 4, p. 585-603Article, review/survey (Refereed)
    Abstract [en]

    Rooted in the very fundamental aspects of many chemical phenomena, and for the majority of photochemistry, is the onset of strongly interacting electronic configurations. To describe this challenging regime of strong electron correlation, an extraordinary effort has been put forward by a young generation of scientists in the development of theories 'beyond' standard wave function and density functional models. Despite their encouraging results, a twenty-and-more-year old approach still stands as the gold standard for these problems: multiconfiguration second-order perturbation theory based on complete active space reference wave function (CASSCF/CASPT2). We will present here a brief overview of the CASSCF/CASPT2 computational protocol, and of its role in our understanding of chemical and photochemical processes.

  • 149. Roca-Sanjuan, Daniel
    et al.
    Delcey, Mickael G.
    Navizet, Isabelle
    Ferre, Nicolas
    Liu, Ya-Jun
    Lindh, Roland
    WARNING: The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!2012Conference paper (Other academic)
  • 150. Roca-Sanjuan, Daniel
    et al.
    Farahani, Pooria
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Frances-Monerris, Antonio
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Engineering Chemiluminescent Properties by Means of Non-Adiabatic Computational Chemistry2014In: Luminescence (Chichester, England Print), ISSN 1522-7235, E-ISSN 1522-7243, Vol. 29, p. 43-43Article in journal (Other academic)
12345 101 - 150 of 201
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf