Change search
Refine search result
123 1 - 50 of 127
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.
  • 1.
    Ahlstrand, Emma
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Spångberg, Daniel
    Universitet Uppsala.
    Hermansson, Kersti
    Universitet Uppsala.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Interaction energies between metal ions (Zn2+ and Cd2+) and biologically relevant ligands2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 23, p. 2554-2562Article in journal (Refereed)
    Abstract [en]

    Interactions between the group XII metals Zn2+ and Cd2+ and amino acid residues play an important role in biology due to the prevalence of the first and the toxicity of the second. Estimates of the interaction energies between the ions and relevant residues in proteins are however difficult to obtain. This study reports on calculated interaction energy curves for small complexes of Zn2+ or Cd2+ and amino acid mimics (acetate, methanethiolate, and imidazole) or water. Given that many applications and models (e.g., force fields, solvation models, etc.) begin with and rely on an accurate description of gas-phase interaction energies, this is where our focus lies in this study. Four density functional theory (DFT)-functionals and MP2 were used to calculate the interaction energies not only at the respective equilibrium distances but also at a relevant range of ion–ligand separation distances. The calculated values were compared with those obtained by CCSD(T). All DFT-methods are found to overestimate the magnitude of the interaction energy compared to the CCSD(T) reference values. The deviation was analyzed in terms of energy components from localized molecular orbital energy decomposition analysis scheme and is mostly attributed to overestimation of the polarization energy. MP2 shows good agreement with CCSD(T) [root mean square error (RMSE) = 1.2 kcal/mol] for the eight studied complexes at equilibrium distance. Dispersion energy differences at longer separation give rise to increased deviations between MP2 and CCSD(T) (RMSE = 6.4 kcal/mol at 3.0 Å). Overall, the results call for caution in applying DFT methods to metalloprotein model complexes even with closed-shell metal ions such as Zn2+ and Cd2+, in particular at ion–ligand separations that are longer than the equilibrium distances.

  • 2.
    Ahlstrand, Emma
    et al.
    Linnæus University Centre for Biomaterials Chemistry.
    Spångberg, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Friedman, Ran
    Interaction Energies Between Metal Ions (Zn2+ and Cd2+) and Biologically Relevant Ligands2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 23, p. 2554-2562Article in journal (Refereed)
    Abstract [en]

    Interactions between the group XII metals Zn2+ and Cd2+ and amino acid residues play an important role in biology due to the prevalence of the first and the toxicity of the second. Estimates of the interaction energies between the ions and relevant residues in proteins are however difficult to obtain. This study reports on calculated interaction energy curves for small complexes of Zn2+ or Cd2+ and amino acid mimics (acetate, methanethiolate, and imidazole) or water. Given that many applications and models (e.g., force fields, solvation models, etc.) begin with and rely on an accurate description of gas-phase interaction energies, this is where our focus lies in this study. Four density functional theory (DFT)-functionals and MP2 were used to calculate the interaction energies not only at the respective equilibrium distances but also at a relevant range of ion–ligand separation distances. The calculated values were compared with those obtained by CCSD(T). All DFT-methods are found to overestimate the magnitude of the interaction energy compared to the CCSD(T) reference values. The deviation was analyzed in terms of energy components from localized molecular orbital energy decomposition analysis scheme and is mostly attributed to overestimation of the polarization energy. MP2 shows good agreement with CCSD(T) [root mean square error (RMSE) = 1.2 kcal/mol] for the eight studied complexes at equilibrium distance. Dispersion energy differences at longer separation give rise to increased deviations between MP2 and CCSD(T) (RMSE = 6.4 kcal/mol at 3.0 Å). Overall, the results call for caution in applying DFT methods to metalloprotein model complexes even with closed-shell metal ions such as Zn2+ and Cd2+, in particular at ion–ligand separations that are longer than the equilibrium distances.

  • 3.
    Ai, Yuejie
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Cui, Ganglong
    Beijing Normal University.
    Fang, Qiu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fang, Weihai
    Beijing Normal University.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Exploring concerted effects of base pairing and stacking on the excited-state nature of DNA oligonucleotides by DFT and TD-DFT studies2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 10, p. 2366-2377Article in journal (Refereed)
    Abstract [en]

    We have taken (dA)5, (dT)5, and (dA)5•(dT)5 as model systems to study concerted effects of base pairing and stacking on excited-state nature of DNA oligonucleotides using density functional theory (DFT) and time dependent DFTmethods. The spectroscopic states are determined to be of a partial A →A charge transfernature in the A•T oligonucleotides. The T → T charge-transfer transitionsproduce dark states, which are hidden in the energy region of the steady-stateabsorption spectra. This is different from the previous assignment that the T → Tcharge-transfer transition is responsible for a shoulder at the red side of the first strongabsorption band. The A →T charge-transfer states were predicted to have relativelyhigh energies in the A•T oligonucleotides. The present calculations predict that the T→A charge-transfer states are not involved in the spectra and excited-state dynamics ofthe A•T oligonucleotides. In addition, the influence of base pairing and stacking on thenature of the 1nΠ* and 1ΠΠ* states are discussed in detail.

  • 4.
    Arteca, Gustavo A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Rank, Jean Pierre
    Tapia, Orlando
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Generalized electronic diabatic approach to structural similarity in two-dimensional potential energy surfaces of various topologies2008In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 108, no 4, p. 651-666Article in journal (Refereed)
    Abstract [en]

    Active site properties in some proteins can be affected by conformational fluctuations of neighbor residues, even when the latter are not involved directly in the binding process. A local environment thus appears to alter the relevant potential energy surface and its reaction paths. Here, some aspects of this phenomenon are simulated within a generalized electronic diabatic (GED) scheme to study the geometry and structural similarity for a class of two-dimensional (2D) energy surfaces. The electronic quantum state is a linear superposition of diabatic basis functions, each of which is taken to represent a single (pure) electronic state for the isolated material system. Here, we describe a model reaction of isomerization by shifts in amplitudes for three diabatic species (reactant, product, and an open-shell transition state) coupled in an external field. The "effective" 2D energy surface in the field is characterized in terms of critical points, and the amplitudes along the main reaction paths. A new feature is the introduction of a phase diagram where all possible potential-energy-surface topologies (consistent with three-state systems in two linear coordinates) are matched with actual model parameters. By varying the coupling strengths between diabatic states, we classify regions of this phase diagram in terms of electronic and structural similarities; some regions comprise models whose reaction paths have geometries that belong to the catchment region of the reactant, yet are electronically akin to the diabatic transition state or product.

  • 5.
    Arteca, Gustavo A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Tapia, Orlando
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Generalized electronic diabatic approach to structural similarity and the Hammond postulate2007In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 107, no 2, p. 382-395Article in journal (Refereed)
    Abstract [en]

    We revisit the notion of structural similarity along a reaction path within the context of a generalized electronic diabatic (GED) molecular model. In this approach, a reaction involving two closed-shell stable species is described as the evolution of a quantum state that superimposes at least three diabatic electronic species (reactant, product, and an open-shell transition state) coupled by an external electromagnetic field. Reactant and product amplitudes in this general state are also modulated by changing the geometry of a system of classical positive charges interacting with the electrons. By mapping these amplitudes over nuclear configurational space, we can follow the total quantum state along a reaction coordinate and establish its similarity to each of the diabatic species. As a result, chemical processes, and useful notions such as those of energy barriers and the Hammond postulate, emerge as consequence of Franck-Condon-like transitions between quantum states.

  • 6.
    Arteca, Gustavo
    et al.
    Département de Chimie et Biochimie and Biomolecular Sciences Programme, Laurentian University.
    Rank, Jean Pierre
    Département de Chimie et Biochimie and Biomolecular Sciences Programme, Laurentian University.
    Tapia, Orlando
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Simulating trends in reaction path geometry as a function of external fields: A generalized electronic diabatic model for two-dimensional energy surfaces2008In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 108, no 10, p. 1810-1820Article in journal (Refereed)
    Abstract [en]

    We introduce a protocol to represent quantum states as a linear superposition of model electronic diabatic basis states coupled in an external (static) elec. field. By considering an entire family of these models, we uncover trends in reaction-path geometry and the topol. of potential-energy surfaces, including all those that can be realized in a two-dimensional configurational space. Our approach can be used as a tool to model the key parameters (e.g., diabatic basis states, external field intensity) that yield desired geometrical characteristics in an actual potential energy surface. In this work, external agents such as laser fields, or a group of neighboring charges, are regarded as essential requirements to prompt, or trigger, the occurrence of a chem. process. In these cases, reaction path geometry can be modulated externally so as to yield processes that would appear to occur far from gas-phase geometries. This phenomenol. is intrinsically nonadiabatic. Our present approach accounts for the possibility of such features, i.e., the occurrence of quantum states whose electronic structures resemble products, while at geometries that are more similar to those of reactants.

  • 7. Bakker, Albert
    et al.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Lindgren, Jan
    Probst, Michael M
    Bopp, Philippe A
    Interaction of aluminum(III) with water. An ab initio study1999In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 75, no 4-5, p. 659-669Article in journal (Refereed)
    Abstract [en]

    Hydrated Al(3+) ions [Al(H(2)O)(n)](3+), n = 1-6, were examined with ab Initio self-consistent field (SCF) calculations. The relative contributions of two-, three-, and higher-body terms to the total interaction energy for an [Al(H(2)O)(6)](3+) complex were calculated The sum of all three-body contributions amounts to - 30% of the sum of all pair-additive contributions and is opposite in sign. The three-body energy contributions were also derived for two types of [Al(H(2)O)(2)](3+) complexes. in the first type, both water molecules reside in the first hydration shell of Al(3+) and in the second type there is one in the first shell and one in the second. Altogether 15,500 triplets were investigated and analytical two- and three-body potential energy functions were derived via a fitting procedure. (C) 1999 John Wiley & Sons, Inc.

  • 8.
    Bengtson, Charlotta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Stenrup, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Quantum nonlocality in the excitation energy transfer in the Fenna-Matthews-Olson complex2016In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 116, p. 1763-1771Article in journal (Refereed)
    Abstract [en]

    The Fenna-Matthews-Olson (FMO) complex - a pigment protein complex involved in photosynthesis in green sulfur bacteria - is remarkably efficient in transferring excitation energy from light harvesting antenna molecules to a reaction center. Recent experimental and theoretical studies suggest that quantum coherence and entanglement may play a role in this excitation energy transfer (EET). We examine whether bipartite quantum nonlocality, a property that expresses a stronger-than-entanglement form of correlation, exists between different pairs of chromophores in the FMO complex when modeling the EET by the hierarchically coupled equations of motion method. We compare the results for nonlocality with the amount of bipartite entanglement in the system. In particular, we analyze in what way these correlation properties are affected by different initial conditions. It is found that bipartite nonlocality only exists when the initial conditions are chosen in an unphysiological manner and probably is absent when considering the EET in the FMO complex in its natural habitat. It is also seen that nonlocality and entanglement behave quite differently in this system. In particular, for localized initial states, nonlocality only exists on a very short time scale and then drops to zero in an abrupt manner. As already known from previous studies, quantum entanglement between chromophore pairs on the other hand is oscillating and exponentially decaying and follow thereby a pattern more similar to the chromophore population dynamics. The abrupt disappearance of nonlocality in the presence of nonvanishing entanglement is a phenomenon we call nonlocality sudden death; a striking manifestation of the difference between these two types of correlations in quantum systems. 

  • 9. Bischof, Gerhard
    et al.
    Silbernagl, Alexander
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
    Probst, Michael
    Quantum chemical study of the molecular dynamics of hydrated Li+ and Be2+ cations1997In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 65, no 5, p. 803-816Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations of clusters of Li+ and Be2(+) cations with up to 12 water molecules were performed calculating the particle trajectories using Hartree-Fock-derived forces. It was found that independent of the starting configuration tetrahedral clusters are obtained in less than 1 ps. Only for Li+ clusters, transition states with five and three water molecules are found. We discuss the structures of the clusters and the vibrational dynamics of the water molecules and compare them with other ab initio simulations, with simulations using analytical potential functions, and with static calculations. Water-dissociation (hydrogen transfer) reactions which take place at elevated temperatures were investigated. (C) 1997 John Wiley & Sons, Inc.

  • 10.
    Björkman, Torbjörn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adaptive Smearing for Brillouin Zone Integration2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 5, p. 1025-1030Article in journal (Refereed)
    Abstract [en]

    We suggest a simple scheme for automatically determining the width parameter of smearing methods of the Brillouin zone integration in electronic structure calculation. The scheme retains one free parameter that at any time can be eliminated by choosing a denser k-space mesh until the desired accuracy is obtained. The tests are carried out in the context of Methfessel-Paxton smearing. This adaptive Gaussian smearing (AGS) is easily implemented, variational with respect to partial occupancies and free from spurious occupancies that are negative or larger than one. Its convergence properties are similar to those obtained with the modified tetrahedron method for energy resolution of >= 0.1 meV.

  • 11.
    Blomberg, Margareta R. A.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    How Quantum Chemistry Can Solve Fundamental Problems in Bioenergetics2015In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 115, no 18, p. 1197-1201Article in journal (Refereed)
    Abstract [en]

    Three different enzymes are discussed, cytochrome c oxidase, involved in aerobic respiration, cytochrome c dependent nitric oxide reductase, involved in denitrification (anaerobic respiration), and photosystem II, involved in photosynthesis. For all three systems, free energy profiles for the entire catalytic cycle are obtained from quantum mechanical calculations on large cluster models of the active sites, using hybrid density functional theory with the B3LYP* functional. The free energy pro-files are used to solve different fundamental problems concerning energy conservation, enzymatic reaction mechanisms and structure, and also to explain experimental results that seem to be in conflict with each other. Possible future applications to related problems using similar methodology are suggested.

  • 12. Bondarchuk, S. V.
    et al.
    Minaev, Boris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fesak, A. Y.
    Theoretical study of the triplet state aryl cations recombination: A possible route to unusually stable doubly charged biphenyl cations2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 24, p. 2580-2588Article in journal (Refereed)
    Abstract [en]

    The self-recombination reactions of 4-aminophenyl cations and parent phenyl cations, each in ground triplet states, are studied within the framework of density functional theory. Only the total zero spin (singlet state) is chosen, as the quintet and triplet counterparts are nonreactive in these systems. The recombination products are the benzidine and biphenyl doubly charged cations. These species are unexpectedly stable. The transition state of the 4-aminophenyl cations reaction is located at the distance of about 4.0 Å between the ipso-carbon atoms. The activation barrier is predominantly formed by electrostatic repulsion between two cations and is estimated to be 27.6 kcal mol-1 [B3LYP/6-311+G(d,p)]. Similar results are obtained for the phenyl cations recombination. The general importance of the participation of other aryl cations in analogous organic reactions is discussed. © 2013 Wiley Periodicals, Inc. The chemical reactivity of diamagnetic molecules is largely determined by the properties of their triplet excited states rather than their closed-shell ground singlet state. As an example of this type of "spin-catalysis," the self-recombination reaction of the triplet state 4-aminophenyl cations leads to the formation of the benzidine dication. The corresponding transition state is "reactant-like" and located at the CipsoCipso interatomic distance of 4.0 Å.

  • 13. Boström, Jonas
    et al.
    Veryazov, Valera
    Aquilante, Francesco
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Bondo Pedersen, Thomas
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Analytical gradients of the second-order Møller–Plesset energy using Cholesky decompositions2014In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 114, no 5, p. 321-327Article in journal (Refereed)
    Abstract [en]

    An algorithm for computing analytical gradients of the second-order Møller–Plesset (MP2) energy using density fitting (DF) is presented. The algorithm assumes that the underlying canonical Hartree–Fock reference is obtained with the same auxiliary basis set, which we obtain by Cholesky decomposition (CD) of atomic electron repulsion integrals. CD is also used for the negative semidefinite MP2 amplitude matrix. Test calculations on the weakly interacting dimers of the S22 test set (Jurečka et al., Phys. Chem. Chem. Phys. 2006, 8, 1985) show that the geometry errors due to the auxiliary basis set are negligible. With double-zeta basis sets, the error due to the DF approximation in intermolecular bond lengths is better than 0.1 pm. The computational time is typically reduced by a factor of 6–7.

  • 14.
    Bredenberg, Johan
    et al.
    Södertörn University, Avdelning Naturvetenskap.
    Nilsson, L
    Modeling zinc sulfhydryl bonds in zinc fingers2001In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 83, no 3-4, p. 230-244Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations have been carried out employing three different model descriptions of the zinc sulfhydryl interactions in class II fingers. One bonded and two nonbonded models were studied. Two variant structures of the glucocorticoid receptor DNA-binding; domain and a NMR structure from a fragment of methionyl-tRNA synthetase were subjected to long-time MD simulations with these models. Our analysis is focused on comparison with experimental and quantum mechanical data, concerning the local Zn-finger and overall structural and dynamic properties for these models. All models performed M ell, but the nonbonded models appeared to reproduce the protein dynamics in better agreement with experimental data than does the bonded description.

  • 15.
    Brändas, Erkki
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    The Statement of Goals of the International Society for Theoretical Chemical Physics2014In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 114, p. 961-962Article in journal (Refereed)
  • 16.
    Brändas, Erkki
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Mathematics and Science.
    Goscinski, Osvaldo
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Mathematics and Science.
    Darboux functions and power series expansions with examples from isoelectronic sequences1972In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 6, no S6, p. 59-72Article in journal (Refereed)
    Abstract [en]

    A procedure for summing a power series based on a Darboux function ansatz is developed. It involves computation of poles and residues of logarithmic derivatives using rational functions. Applications to the helium isoelectronic sequence condense the power series expansion (˜ 40 coefficients) to a few-parameter formula, which exhibits the singularity determining the radius of convergence. Accurate extrapolations of electron affinities and shielding factors are obtained.

  • 17.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
    A theorem for complex symmetric matrices revisited.2009In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 109, no 13, p. 2860-2865Article in journal (Refereed)
    Abstract [en]

    In this contribution we will revisit the celebrated theorem that every   square matrix is similar to a (complex) symmetric matrix and that every   symmetric matrix is orthogonally similar to a given normal canonical   form. Specifically we will re-examine the proof as well as the   derivation of an explicit n-dimensional complex symmetric form. We will   extend the formula to incorporate the various powers of the original   normal form, a derivation not previously provided. Some examples of   these complex symmetric forms in chemical and physical applications are   indicated.

  • 18.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Arrows of Time and Fundamental Symmetries in Chemical Physics2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 3, p. 173-184Article in journal (Refereed)
    Abstract [en]

    The field of chemical and physical processes, using principal microscopic techniques, should today allegedly be identified as a fundamental branch of physics. The discipline, by tradition known as chemical physics, is undergoing rapid progress. This assessment, illustrated by the advances presented at this Congress, is characterized by modern developments and novel trends with a concrete bearing on original theoretical understanding, with the possibility to go beyond traditional interpretations and explanations. In this vein, we do not only consider nonrelativistic treatments of various types of molecules including interactions between these and polymers, theoretical examinations of chemical reactions, surface states and interface states, disordered phenomena etc., but also recent progress together with non-Hermitian extensions to quantum mechanics and statistical mechanics. The latter leads to a united edifice of theoretical constructions including the law of self-reference, which emerges in analogy with the illustrious Gödel theorem(s) of mathematical logic, that is, the assertion of the inherent limitations of all nontrivial axiomatic systems. The current development begets the foundation of temporal processes and associated invariance principles including the valuation of the various arrows of time. The present conjugate operator array formulation supports the possible gravitational origin of molecular chirality and other principal symmetry violations.

  • 19.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Arrows of time and fundamental symmetries in chemical physics2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 3, p. 173-184Article in journal (Refereed)
    Abstract [en]

    The field of chemical and physical processes, using principal microscopic techniques, should today allegedly be identified as a fundamental branch of physics. The discipline, by tradition known as chemical physics, is undergoing rapid progress. This assessment, illustrated by the advances presented at this Congress, is characterized by modern developments and novel trends with a concrete bearing on original theoretical understanding, with the possibility to go beyond traditional interpretations and explanations. In this vein, we do not only consider nonrelativistic treatments of various types of molecules including interactions between these and polymers, theoretical examinations of chemical reactions, surface states and interface states, disordered phenomena etc., but also recent progress together with non-Hermitean extensions to quantum mechanics and statistical mechanics. The latter leads to a united edifice of theoretical constructions including the law of self-reference, which emerges in analogy with the illustrious Godel theorem(s) of mathematical logic, that is, the assertion of the inherent limitations of all nontrivial axiomatic systems. The current development begets the foundation of temporal processes and associated invariance principles including the valuation of the various arrows of time. The present conjugate operator array formulation supports the possible gravitational origin of molecular chirality and other principal symmetry violations.

  • 20.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Godelian Structures and Self-Organization in Biological Systems2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 7-8, p. 1321-1332Article in journal (Refereed)
    Abstract [en]

    In 1986, Seel and Ladik asked, which role Godel's incompleteness theorem should have in a basic theory of biology. Recently, the author has tried to collect the conditions, which such a meta-theory must fulfill. A further argument concerned the deeper connection between classical canonical forms of so-called (triangular) Jordan blocks in the description of open quantal systems far from equilibrium and those of self-referential contradictions and paradoxes in philosophy and mathematical logic. Related examples were quoted from the emergence of self-organization in so-called dissipative structures with applications to both fundamental-and of higher order levels of organization. To bring this analogy closer together, we have developed a quantum logical formalism, describing such a Godelian situation, via the characterization of a well-defined "truth matrix." In this setting, the modus operandi of exploiting self-referential traits and paradoxical inconsistencies emphasize the possibility of a meta-code in complicated enough (biological) systems. In conclusion, we will revisit situations were the aforementioned self-referential property, together with the laws of physics and chemistry will guide our understanding of biology. We will finally consider subsequent implications on the various positions on artificial intelligence.

  • 21.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
    Microscopic self-organization and self-referential systems: a progress report.2009In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 109, no 14, p. 3500-3504Article in journal (Refereed)
    Abstract [en]

    It is contended that (the classical canonical form of) Jordan blocks, play a role analogous to those of paradoxes and self-referential contradictions in philosophy and mathematical logic. As examples we will briefly discuss the occurrence of such triangular units in appropriately generalized quantum theory of microscopic as well as open dissipative systems with structures appearing on both the fundamental as well as in higher order levels of organization. The mathematical structure centers on specific transformations within coherent-dissipative ensembles that exhibit certain factorization properties allowing prime number algorithms, cf. the Godel encoding system used to derive the celebrated incompleteness theorem. This prompts the suggestion that an additional meta-code, cf. the genetic code, might be a-scripted for the mapping between the genotype and phenotype spaces.

  • 22.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Non-hermitian quantum mechanics2012In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 112, no 15, p. 2764-2765Article, book review (Other academic)
  • 23.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Some Comments on the Problem of Decoherence2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 2, p. 215-224Article in journal (Refereed)
    Abstract [en]

    We consider a universally valid superposition principle derived from a general complex symmetric ansatz. The approach concerns open, dissipative systems and its significance for the examination and analysis of system-environment correlations. In particular, we discuss the concept of decoherence in the ensuing fundamental operator equations, incorporating simultaneously holistic and classical regimes. Despite its reductionist character, the theory applies to both micro-and macroscopic systems. Examples are drawn from general relativity, for example, the law of light deflection, the gravitational redshift, the time delay and the perihelion motion of Mercury, and from the macroscopic domain, for example, the emergence of selforganization in complicated enough systems. The preceding portrayal commends autonomicity and provides legitimate concepts of central importance in biological organization and artificial intelligence.

  • 24.
    Brändas, Erkki
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Szabados, Ágnes
    Eötvös Loránd University.
    Surján, Péter
    Eötvös Loránd University.
    Preface: Eighth Congress of the International Society for Theoretical ChemicalPhysics (ISTCP-VIII)2014In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 114, p. 959-960Article in journal (Refereed)
  • 25. Bunta, Juraj
    et al.
    Dahlberg, Martin
    Eriksson, Leif A.
    Örebro University, Department of Natural Sciences.
    Korolev, Nikolai
    Laaksonen, Aatto
    Lohikoski, Raimo
    Lyubartsev, Alexander
    Pinak, Miroslav
    Schyman, Patric
    Solvating, manipulating, damaging, and repairing DNA in a computer2007In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 107, no 2, p. 279-291Article in journal (Refereed)
    Abstract [en]

    This work highlights four different topics in modeling of DNA: (i) the importance of water and ions together with the structure and function of DNA; the hydration structure around the ions appears to be the determining factor in the ion coordination to DNA, as demonstrated in the results of our MD simulations; (ii) how MD simulations can be used to simulate single molecule manipulation experiments as a complement to reveal the structural dynamics of the studied biomolecules; (iii) how damaged DNA can be studied in computer simulations; and (iv) how repair of damaged DNA can be studied theoretically.

  • 26.
    Bustad, Johnny
    et al.
    University of Gävle, Department of Mathematics, Natural and Computer Sciences, Ämnesavdelningen för naturvetenskap.
    Lunell, C
    Semi-empirical configurational interaction calculation of shake-up satellites in Ni(CO)41998In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, International journal of Quantum Chemistry, Vol. 69, no 5, p. 649-657Article in journal (Refereed)
    Abstract [en]

    INDO/CI calculations were used to analyze the C1s and O1s shake-up spectra of nickel tetracarbonyl, Ni(CO)4. The satellite structure in both cases is dominated by excitations from metal–ligand bonding (2Πb) to metal–ligand antibonding (2Πa) orbitals and by excitations within the core-ionized CO molecule, ΠCO—Π*CO.

  • 27.
    Carlsen, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
    Goscinski, Osvaldo
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
    Quantal trajectories for adiabatic and nonadiabatic regimes of vibronic systems1999In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 75, no 4-5, p. 409-416Article in journal (Refereed)
    Abstract [en]

    Exact and averaged nuclear pseudorotational quantal trajectories are compared for Various adiabatic and vibronic states of the Longuet-Higgins E x epsilon Jahn-Teller model. It is argued that the usual averaging over the electronic motion could be understood as being a consequence of ergodicity. The failure of the Born-Oppenheimer factorization to obey the ergodic hypothesis was examined. A quantitative separation of the electronic and nuclear time-scales is, nevertheless, achieved for all regimes. It is shown that the short-time deviations from the global "drift" of the electronic and nuclear motions are perfectly correlated.

  • 28. Chen, Shu-Feng
    et al.
    Yue, Ling
    Liu, Ya-Jun
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Multireference theoretical studies on the solvent effect of firefly multicolor bioluminescence2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 13, p. 3371-3377Article in journal (Refereed)
    Abstract [en]

    In concert with the recent spectroscopic studies of the light-color modulation mechanism of firefly (Hirano et al., J Am Chem Soc 2009, 131, 2385), quantum chemical calculations using complete active space SCF (CASSCF), multistate complete active space second order perturbation (MS-CASPT2) theory as well as a time-dependent density functional theory (TD-DFT) approach with the Coulomb attenuated hybrid exchange-correlation functional (CAM-B3LYP) were performed on the excited state (S1) of the keto-form oxyluciferin (keto-OxyLH2). Benzene, DMSO, CH3CN, and H2O were chosen as polar solvents. The polarization effect of less polar solvent was considered by a simple model, complex of keto-OxyLH2, and NH3 with different covalent character. The calculated results supported the experimental conclusion: (1) the light emitter of bioluminescence is the S1 state of keto-OxyLH2 anion [(keto-1)*], and (2) light emission from (keto-1)* is modulated by the polarity of surrounding environment and the degree of covalent character of hydrogen bond between (keto-1)* and a protonated basic moiety. The mechanism of the multicolor bioluminescence was discussed from the theoretical viewpoint.

  • 29. Cicero, Giancarlo
    et al.
    Carbonera, Chiara
    Valegård, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Hajdu, Janos
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Andersson, Inger
    Ranghino, Graziella
    Study of the oxidative half-reaction catalyzed by a non-heme ferrous catalytic center by means of structural and computational methodologies2007In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 107, no 6, p. 1514-1522Article in journal (Refereed)
    Abstract [en]

    Deacetoxycephalosporin C synthase (DAOCS) is a mononuclear ferrous enzyme that catalyzes the expansion of the five-membered thiazolidine ring of the penicillin nucleus into the six-membered dihydrothiazine ring of the cephalosporins. In the first half-reaction with dioxygen and 2-oxoglutarate, a reactive iron-oxygen species is produced that can subsequently react with the penicillin substrate to yield the cephalosporin. We describe quantum mechanical calculations of the first part of the reaction based on the high-resolution structures of the active site of DAOCS and its complexes with ligands. These studies are aimed at understanding how the reactive species can be produced and contained in the active site of the enzyme. The results demonstrate the priming of the active site by the co-substrate for oxygen binding and hint to the presence of a stable iron-peroxo intermediate in equilibrium with a more reactive ferryl species and the formation of CO2 as a leaving group by decarboxylation of 2-oxoglutarate. A conclusion from these studies is that substitution of CO2 by the penicillin substrate triggers the oxidation reaction in a booby-trap-like mechanism.

  • 30. Cicero, Giancarlo
    et al.
    Carbonera, Chiara
    Valegård, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Hajdu, Janos
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Andersson, Inger
    Ranghino, Graziella
    Study of the oxidative half-reaction catalyzed by a non-heme ferrous catalytic center by means of structural and computational methodologies2007In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 107, no 6, p. 1514-1522Article in journal (Refereed)
    Abstract [en]

    Deacetoxycephalosporin C synthase (DAOCS) is a mononuclear ferrous enzyme that catalyzes the expansion of the five-membered thiazolidine ring of the penicillin nucleus into the six-membered dihydrothiazine ring of the cephalosporins. In the first half-reaction with dioxygen and 2-oxoglutarate, a reactive iron-oxygen species is produced that can subsequently react with the penicillin substrate to yield the cephalosporin. We describe quantum mechanical calculations of the first part of the reaction based on the high-resolution structures of the active site of DAOCS and its complexes with ligands. These studies are aimed at understanding how the reactive species can be produced and contained in the active site of the enzyme. The results demonstrate the priming of the active site by the co-substrate for oxygen binding and hint to the presence of a stable iron-peroxo intermediate in equilibrium with a more reactive ferryl species and the formation of CO2 as a leaving group by decarboxylation of 2-oxoglutarate. A conclusion from these studies is that substitution of CO2 by the penicillin substrate triggers the oxidation reaction in a booby-trap-like mechanism.

  • 31. Cicero, Giancarlo
    et al.
    Carbonera, Chiara
    Valegård, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Hajdu, Janos
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
    Andersson, Inger
    Ranghino, Graziella
    Study of the oxidative half-reaction catalyzed by a non-heme ferrous catalytic center by means of structural and computational methodologies2007In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 107, no 6, p. 1514-1522Article in journal (Refereed)
    Abstract [en]

    Deacetoxycephalosporin C synthase (DAOCS) is a mononuclear ferrous enzyme that catalyzes the expansion of the five-membered thiazolidine ring of the penicillin nucleus into the six-membered dihydrothiazine ring of the cephalosporins. In the first half-reaction with dioxygen and 2-oxoglutarate, a reactive iron-oxygen species is produced that can subsequently react with the penicillin substrate to yield the cephalosporin. We describe quantum mechanical calculations of the first part of the reaction based on the high-resolution structures of the active site of DAOCS and its complexes with ligands. These studies are aimed at understanding how the reactive species can be produced and contained in the active site of the enzyme. The results demonstrate the priming of the active site by the co-substrate for oxygen binding and hint to the presence of a stable iron-peroxo intermediate in equilibrium with a more reactive ferryl species and the formation of CO2 as a leaving group by decarboxylation of 2-oxoglutarate. A conclusion from these studies is that substitution of CO2 by the penicillin substrate triggers the oxidation reaction in a booby-trap-like mechanism.

  • 32. Crespo, R.
    et al.
    Piqueras, M-C
    Aullo, J. M.
    Tapia, Orlando
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    A Theoretical Study of Semiclassic Models: Toward a Quantum Mechanical Representation of Chemical Processes2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 2, p. 263-271Article in journal (Refereed)
    Abstract [en]

    CASPT2 level of theory and aug-cc-pV6Z atomic basis set for hydrogen and 6 base states is sufficient to accurately reproduce the historical calculations of Kolos-Wolniewicz for H-2(1) Sigma(+)(g) potential energy curve. We found that for H + H process experimental and adiabatic theory results are contradictory. By analyzing different levels of semiclassic theory, we identify the nature of the failure. We propose an approximate scheme that may bridge semiclassic to QM model.

  • 33. de Almeida, K. J.
    et al.
    Ramalho, T. C.
    Alves, M. C.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical insights into the visible near-infrared absorption spectra of Bis(hexafluoroacetylacetonate) copper(II) in pyridine2012In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 112, no 13, p. 2571-2577Article in journal (Refereed)
    Abstract [en]

    The density functional theory calculations were performed to investigate the specific solvent effects on the optical absorption spectrum of copper(II) hexafluoroacetylacetonate complex in pyridine. The effects of single and double coordination of pyridine molecules at axial position of bis(hexafluoroacetylacetonate) copper(II) indicate that both positions and intensities of 3d3d electronic transitions are strongly dependent on the coordination environment around the copper(II) complex. The results indicate that the nature of the electron-acceptor atoms in the equatorial ligands plays an important role in the number of solvent molecules in the first solvation shell of copper(II) acac systems.

  • 34.
    de Marothy, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Autocatalytic decomposition of carbonic acid2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 20, p. 2306-2311Article in journal (Refereed)
    Abstract [en]

    Long held to be unstable or metastable in the gas phase, carbonic acid has successfully been produced and identified in its gaseous form in recent decades. Theoretical studies have indicated that isolated carbonic acid in the gas phase may in fact be quite stable, its decomposition attributable to the catalytic effect of water molecules, either present or produced in a chain reaction by an initially slow decomposition. In this study, a previously unreported autocatalytic decomposition route is studied using high-accuracy ab initio quantum chemical methods. Results indicate that a carbonic acid dimer may react and decompose in a single-step, highly concerted reaction. The transition state of this reaction was characterized, and the reaction pathway was found to have significantly lower activation energy than the uncatalyzed decomposition, and comparable or lower energy than the water-catalyzed reaction. The results indicate that gaseous carbonic acid should be unstable even in the absence of water.

  • 35. Delgado-Barrio, Gerardo
    et al.
    Maruani, Jean
    Piecuch, Piotr
    Brändas, Erkki
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Special Issue: Proceedings from the Fourteenth European Workshop on Quantum Systems in Chemistry and Physics Preface2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 2, p. 203-204Article in journal (Other academic)
  • 36. Devarajan, Ajitha
    et al.
    Gaenko, Alexander
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Malmqvist, Per-Åke
    Role of Electronic Curve Crossing of Benzene S-1 State in the Photodissociation of Aryl Halides, Effect of Fluorination: RASSI-SO MS-CASPT2 Study2009In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 109, no 9, p. 1962-1974Article in journal (Refereed)
    Abstract [en]

    An ab initio study of the role of electronic curve crossing of benzene S-1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low-lying n-sigma*, pi-sigma*, pi-pi* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene pi-pi* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low-lying n-sigma*, pi-sigma*, pi-pi* states were studied including spin-orbit and relativistic effects using the Restricted Active Space state interaction multistate complete active space perturbation theory (RASSI-MS-CASPT2) method. Crossing behavior of spin-free and spin-orbit potential energy curves was analyzed for the role of the benzene S-1 state. Our results indicate the curve crossing region to be around 2.00-2.35 angstrom for both C6H5I and C6F5I. Analysis of effect of fluorination on the energies of states corresponding to benzene pi-pi* and n-sigma* transitions suggests an increase in the energy of benzene pi-pi* states and a decrease in the energy of the states corresponding to n-sigma* transitions. Increased spin-orbit gap, increased separation of the benzene S-1(pi-pi*) state and n-sigma* states in the region of curve crossing, lesser mixing of the pi-pi* and n-sigma* states, an order of magnitude decrease in the transition strength to the benzene singlet transition all contributed to the observed Substantial increase in the quantum yield of the direct channel product on fluorination of aryl halides.

  • 37. Dungsrikaew, V.
    et al.
    Limtrakul, J.
    Hermansson, Kersti
    KTH, Superseded Departments, Biotechnology.
    Probst, M.
    Comparison of methods for point-charge representation of electrostatic fields2004In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 96, no 1, p. 17-22Article in journal (Refereed)
    Abstract [en]

    The calculation of the electrostatic potential resulting from an infinite or extended array of charges in the interior of a region of interest is a frequent task in computational chemistry. In case of a periodic potential this can, for example, be done by Ewald summation or by multipole methods. An important alternative are those methods where arrays of auxiliary point charges are optimized with respect to charge and/or position to reproduce the original electrostatic potential. In the literature different variations are reported. We compare the performance of some of these with respect to their ability to reproduce the original potential and the computational effort required. Between (1) surface charges determined by the conductor-boundary condition, (2) optimized surface charges, and (3) surface charges floating on the surface we find that (2) offers good quality with small computational costs involved.

  • 38.
    Dunne, Lawrence J.
    et al.
    Imperial College London.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Superconductivity from Repulsive Electronic Correlations on Alternant Cuprate and Iron-Based Lattices2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 17, p. 2053-2059Article in journal (Refereed)
    Abstract [en]

    A key question in the theory of high-temperature superconductivityis whether off-diagonal long-range order can beinduced wholly or in large part by repulsive electronic correlations. Electron pairs on cuprate and the iron-based pnictide and chalcogenide alternant lattices may interact with a strong shortrange Coulomb repulsion and much weaker longer range attractive tail. Here, we show that such interacting electrons can cooperate to produce a superconducting state in which time reversed electron pairs effectively avoid the repulsive part but reside predominantly in the attractive region of the potential. The alternant lattice structure is a key feature of such a stabilization mechanism leading to the occurrence of high-temperature superconductivity with dx2y2 or sign alternating s-wave or s-condensate symmetries

  • 39. Dunne, Lawrence J.
    et al.
    Brändas, Erkki J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Superconductivity from repulsive electronic correlations on alternant cuprate and iron-based lattices2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 17, p. 2053-2059Article in journal (Refereed)
    Abstract [en]

    A key question in the theory of high-temperature superconductivity is whether off-diagonal long-range order can be induced wholly or in large part by repulsive electronic correlations. Electron pairs on cuprate and the iron-based pnictide and chalcogenide alternant lattices may interact with a strong short-range Coulomb repulsion and much weaker longer range attractive tail. Here, we show that such interacting electrons can cooperate to produce a superconducting state in which time-reversed electron pairs effectively avoid the repulsive part but reside predominantly in the attractive region of the potential. The alternant lattice structure is a key feature of such a stabilization mechanism leading to the occurrence of high-temperature superconductivity with d(x2-y2) or sign alternating s-wave or s +/- condensate symmetries. 

  • 40.
    Elander, Nils
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Levin, Sergey B.
    Yarevsky, Evgeny
    Convergence and Quantum Number Assignment Studies of Rovibrational Eigenstates in a Model of Predissociating NeICI van der Waals Complex2009In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 109, no 3, p. 459-468Article in journal (Refereed)
    Abstract [en]

    This report details extensions and further analysis of the results presented in an earlier study (Elander et al., Phys Rev A 2001, 64, 012505). Rovibrational resonances in a model of the triatomic van der Waals complex NeICI were studied with a full quantum mechanical, smooth exterior dilation technique realized in a three-dimensional finite element code. Both exact and approximate results, where Coriolis effects are neglected, are presented, and their structures are discussed. Although the helicity is a good quantum number in a one-equation approximation, it is here demonstrated that this is not in the case when including Coriolis coupling, that is, couplings to other helicity components. The behavior of the resonance widths and the positions together with the structure of the resonance wave functions and their dependence on the total angular momentum and its projection have been studied. The dependence of the width of a given resonance oil the total angular momentum was found to be weak while the dependence on the helicity is stronger. 

  • 41.
    Eriksson, Emma S. E.
    et al.
    Örebro University, Department of Natural Sciences.
    Guedes, Rita C.
    Eriksson, Leif A.
    Örebro University, Department of Natural Sciences.
    Redox and debromination reactions of brominated hypericin2008In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 108, no 11, p. 1921-1929Article in journal (Refereed)
    Abstract [en]

    Phototoxic and radical-generating debromination reactions of monobrominated hypericin with bromine at one of four possible positions were investigated using density functional theory. The study was performed on two closely lying conformational isomers, differing in the relative orientations of the two anthracene units of the hypericin core. Calculated adiabatic electron affinities show that the molecules have the ability to, in aqueous solution, extract an electron from the surrounding. The electron might then be passed on to molecular oxygen, forming reactive superoxide radical anions. If electron extraction from the molecule does not occur in this step, the molecule might dissociate, generating a negatively charged bromine as a leaving group and a hypericin radical capable of forming direct binding to biological molecules. This reaction was found possible for those species substituted by Br at two of the four positions, with barriers of 13 kcal/mol in aqueous solution. Debromination was not found energetically possible for neither the neutral ground state compounds nor the bay-deprotonated species.

  • 42.
    Eriksson, Leif A.
    et al.
    Örebro University, Department of Natural Sciences.
    Russo, Nino
    Ugalde, Jesus M.
    Second International Theoretical Biophysics Symposium, Örebro University, Sweden, June 28–July 1, 20052007In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 107, no 2, p. 66p. 259-260Article in journal (Refereed)
  • 43. Eriksson, O.
    et al.
    Wills, J. M.
    Colarieti-Tosti, Massimiliano
    Department of Physics and Measurement Technology, Linkping University.
    Lebègue, S.
    Grechnev, A.
    Many-body projector orbitals for electronic structure theory of strongly correlated electrons2005In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 105, no 2, p. 160-165Article in journal (Refereed)
    Abstract [en]

    We describe a technique to evaluate projector functions to be used, e.g., in self-interaction corrected versions of the Kohn-Sham equation (or in the LSDA+U method). The projector functions reproduce by construction the expectation values of spin and orbital moments (or any other property one is interested in) for the atomic many-body state. We therefore refer to these projector functions as many-body projector orbitals (MBPO). We describe how, once these projector states have been calculated, one can use them in any electronic structure method for a solid or molecule, to calculate ground-state properties of materials with strongly correlated states.

  • 44.
    Eriksson, Olivia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Wills, JM
    Colarieti-Tosti, Massimiliano
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Lebegue, S
    Grechnev, A
    Many-body projector orbitals for electronic structure theory of strongly correlated electrons2005In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 105, no 2, p. 160-165Article in journal (Refereed)
    Abstract [en]

    We describe a technique to evaluate projector functions to be used, e.g., in self-interaction corrected versions of the Kohn-Sham equation (or in the LSDA+U method). The projector functions reproduce by construction the expectation values of spin and orbital moments (or any other property one is interested in) for the atomic many-body state. We therefore refer to these projector functions as many-body projector orbitals (MBPO). We describe how, once these projector states have been calculated, one can use them in any electronic structure method for a solid or molecule, to calculate ground-state properties of materials with strongly correlated states. (c) 2005 Wiley Periodicals, Inc.

  • 45.
    Faber, Felix
    et al.
    University of Basel, Switzerland; University of Basel, Switzerland; University of Basel, Switzerland.
    Lindmaa, Alexander
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    von Lilienfeld, O. Anatole
    University of Basel, Switzerland; Argonne Leadership Comp Facil, IL 60439 USA; Argonne National Lab, IL 60439 USA.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Crystal structure representations for machine learning models of formation energies2015In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 115, no 16, p. 1094-1101Article in journal (Refereed)
    Abstract [en]

    We introduce and evaluate a set of feature vector representations of crystal structures for machine learning (ML) models of formation energies of solids. ML models of atomization energies of organic molecules have been successful using a Coulomb matrix representation of the molecule. We consider three ways to generalize such representations to periodic systems: (i) a matrix where each element is related to the Ewald sum of the electrostatic interaction between two different atoms in the unit cell repeated over the lattice; (ii) an extended Coulomb-like matrix that takes into account a number of neighboring unit cells; and (iii) an ansatz that mimics the periodicity and the basic features of the elements in the Ewald sum matrix using a sine function of the crystal coordinates of the atoms. The representations are compared for a Laplacian kernel with Manhattan norm, trained to reproduce formation energies using a dataset of 3938 crystal structures obtained from the Materials Project. For training sets consisting of 3000 crystals, the generalization error in predicting formation energies of new structures corresponds to (i) 0.49, (ii) 0.64, and (iii) 0.37eV/atom for the respective representations.

  • 46.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    A Simple Approximation for the Pauli Potential Yielding Self-Consistent Electron Densities Exhibiting Proper Atomic Shell Structure2015In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 115, no 23, p. 1629-1634Article in journal (Refereed)
    Abstract [en]

    A simple approximation for the Pauli potential for the groundstate of atomic systems is given, which in connection with Hohenberg-Kohn variational procedure yields self-consistent electron densities exhibiting proper atomic shell structure. (C) 2015 Wiley Periodicals, Inc.

  • 47.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    About the compatibility between ansatzes and constraints for a local formulation of orbital-free density functional theory2017In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 117, no 5, article id UNSP e25329Article in journal (Refereed)
    Abstract [en]

    Functional properties that are exact for the Hohenberg-Kohn functional may turn into mutually exclusive constraints at a given level of ansatz. This is exemplarily shown for the local density approximation. Nevertheless, it is possible to reach exactly the Kohn-Sham data from an orbital-free density functional framework based on simple one-point functionals by starting from the Levy-Perdew-Sahni formulation. The energy value is obtained from the density-potential pair, and therefore does not refer to the functional dependence of the potential expression. Consequently, the potential expression can be obtained from any suitable model and is not required to follow proper scaling behavior.

  • 48.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    About the Difference Between Density Functionals Defined by Energy Criterion and Density Functionals Defined by Density Criterion: Exchange Functionals2016In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 116, no 15, p. 1187-1189Article in journal (Refereed)
    Abstract [en]

    The difference between density functionals defined by energy criterion and density functionals defined by density criterion is studied for the exchange functional. It is shown that Slater potentials are exact exchange potentials in the sense that they yield the Hartree-Fock electron density if all operators are given by local expressions. (C) 2016 Wiley Periodicals, Inc.

  • 49.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Approximating the Pauli Potential in Bound Coulomb Systems2016In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 116, no 16, p. 1261-1266Article in journal (Refereed)
    Abstract [en]

    It is shown that the Pauli potential in bound Coulomb systems can in good approximation be composed from the corresponding atomic fragments. This provides a simple and fast procedure how to generate the Pauli potential in bound systems, which is needed to perform an orbital-free density functional calculation. The method is applicable to molecules and solids. (c) 2016 Wiley Periodicals, Inc.

  • 50.
    Finzel, Kati
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Baranov, Alexey I.
    Max Planck Institute Chemistry Phys Solids, Germany.
    A simple model for the Slater exchange potential and its performance for solids2017In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 117, no 1, p. 40-47Article in journal (Refereed)
    Abstract [en]

    A simple local model for the Slater exchange potential is determined by least square fit procedure from Hartree-Fock (HF) atomic data. Since the Slater potential is the exact exchange potential yielding HF electron density from Levy-Perdew-Sahni density functional formalism (Levy et al., Phys. Rev. A 1984, 30, 2745), the derived local potential is significantly more negative than the conventional local density approximation. On the set of 22 ionic, covalent and van der Waals solids including strongly correlated transition metal oxides, it has been demonstrated, that this simple model potential is capable of reproducing the band gaps nearly as good as popular meta GGA potentials in close agreement with experimental values.

123 1 - 50 of 127
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