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  • 1. Baev, A.
    et al.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Ueda, K.
    de Fanis, A.
    Okada, K.
    Sorensen, S.
    Doppler interference in dissociative resonant photoemission2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, no 2Article in journal (Refereed)
    Abstract [en]

    Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.

  • 2. Baev, A.
    et al.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Quantum-classical modeling of nonlinear pulse propagation in a dissolved two-photon active chromophore2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 11, p. 5379-5385Article in journal (Refereed)
    Abstract [en]

    In the present work we outline the implications of a quantum-classical approach for modeling two-photon absorption of organic chromophores in solution. The approach joins many-photon absorption dynamic simulations with quantum chemical first principles calculations of corresponding excitation energies and transition matrix elements. Among a number of conclusions of the study, we highlight three: (i) The use of either short- or long-pulse excitation is demonstrated to switch the absorptive capacity of the nonlinear medium owing to enhancement of the nonlinear stepwise processes; (ii) The two-photon cross section strongly depends on the way in which the dephasing rate decays when the laser frequency is tuned off-resonant with the corresponding molecular transition; (iii) The results of the pulse propagation simulations based on electronic structure data obtained with a new Coulomb attenuated functional is shown to be in much better agreement with the experimental results than those based on data received with traditional density functionals.

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

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

  • 4. Bast, Radovan
    et al.
    Hesselmann, Andreas
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Helgaker, Trygve
    Saue, Trond
    Static and frequency-dependent dipole-dipole polarizabilities of all closed-shell atoms up to radium: A four-component relativistic DFT study2008In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 9, no 3, p. 445-453Article in journal (Refereed)
    Abstract [en]

    We test the performance of four-component relativistic density functional theory by calculating the static and frequency-dependent electric dipole-dipole polarizabilities of all (ground-state) closed-shell atoms-up to Ra. We consider 12 nonrelativistic functionals, including three asymptotically, shape-corrected functionals, by using two smooth interpolation schemes introduced by the Baerends group: the gradient-regulated asymptotic connection (GRAC) procedure and the statistical averaging of (model) orbital potentials (SAOP). Basis sets of doubly augmented triple-zeta quality are used. The results are compared to experimental data or to accurate ob initio results. The reference static electric dipole polarizability of palladium has been obtained by finite-field calculations using the coupled-cluster singles, doubles, and perturbative triples method within this work. The best overall performance is obtained using hybrid functionals and their GRAC shape-corrected versions. The performance of SAOP is among the best for nonhybrid functionals for Group 18 atoms but its precision degrades when considering the full set of atoms. In general, we find that conclusions based on results obtained for the rare-gas atoms are not necessarily representative of the complete set of atoms. GRAC cannot be used with effective core potentials since the asymptomatic correction is switched on in the core region.

  • 5.
    Bondesson, Laban
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    A linear scaling study of solvent-solute interaction energy of drug molecules in aqua solution2007In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 34, p. 10320-10328Article in journal (Refereed)
    Abstract [en]

    Solvent-solute interaction energies for three well-known drug molecules in water solution are computed at the Hartree-Fock and B3LYP density functional theory levels using a linear scaling technique, which allows one to explicitly include in the model water molecules up to 14 A away from the solute molecule. The dependence of calculated interaction energies on the amount of included solvent has been examined. It is found that it is necessary to account for water molecules within an 8 A radius around the drug molecule to reach the saturated solvent interaction level. Effects of electron correlation and basis set on solvent-solute interaction energies are discussed.

  • 6.
    Bondesson, Laban
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Basis set dependence of solute-solvent interaction energy of benzene in water: a HF/DFT study2008In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 29, no 11, p. 1725-1732Article in journal (Refereed)
    Abstract [en]

    Solute-solvent interaction energies for the benzene molecule dissolved in water are computed using Hartree-Fock and B3LYP density functional theories. Explicit solvent molecules up to 14-angstrom away from the dissolved benzene molecule are included in the calculation of interaction energies. Both basis set dependence and basis Set Superposition errors are carefully examined. It is found that the use of a larger basis set for the region near the solute together with a smaller basis set for the outer region gives results very close to what would have been obtained if the larger basis set had been used for the whole system. It is also shown that a correction for the basis Set superposition error is a necessary component in this kind of calculations. With this correction, results obtained with different tested basis sets converge to within 1 kcal/mol.

  • 7.
    Bondesson, Laban
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Basis set dependence of solvent-solute interaction energy of benzene in water: a linear scaling ab initio studyArticle in journal (Refereed)
  • 8.
    Bondesson, Laban
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Royal Inst Technol, Dept Theoret Chem, SE-10691 Stockholm, Sweden..
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Royal Inst Technol, Dept Theoret Chem, SE-10691 Stockholm, Sweden..
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Royal Inst Technol, Dept Theoret Chem, SE-10691 Stockholm, Sweden..
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Royal Inst Technol, Dept Theoret Chem, SE-10691 Stockholm, Sweden..
    Erratum to: Basis set dependence of solute-solvent interaction energy of benzene in waterA HF/DFT study (vol 29, pg 1725, 2008)2012In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 33, no 3, p. 354-354Article in journal (Refereed)
  • 9. Coriani, Sonia
    et al.
    Host, Stinne
    Jansik, Branislav
    Thogersen, Lea
    Olsen, Jeppe
    Jorgensen, Poul
    Reine, Simen
    Pawlowski, Filip
    Helgaker, Trygve
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Linear-scaling implementation of molecular response theory in self-consistent field electronic-structure theory2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, no 15, p. 11930-11935Article in journal (Refereed)
    Abstract [en]

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

  • 10. Feifel, R
    et al.
    Burmeister, F
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Piancastelli, N
    Bassler, M
    Sorensen, L
    Miron, C
    Wang, H
    Hjelte, I
    Bjorneholm, O
    de Brito, N
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Svensson, S
    Observation of a continuum-continuum interference hole in ultrafast dissociating core-excited molecules2000In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 85, no 15, p. 3133-3136Article in journal (Refereed)
    Abstract [en]

    The femtosecond dissociation of HCl after core excitation has been studied through the resonant Auger decay. The spectra contain contributions from decay occurring at both "molecular" and "atomic" internuclear distances. We have observed a new interference mechanism in these spectra: An atomic spectral line develops into a negative spectral contribution, a "hole," when detuning the excitation energy from the maximum of the Cl 2p(-1)sigma* resonance. Resonant x-ray scattering theory quantitatively explains this behavior as due to a novel destructive continuum-Continuum interference between molecular and atomic contributions to the Auger decay.

  • 11. Feifel, R.
    et al.
    Velkov, Yasen
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Carravetta, V.
    Angeli, C.
    Cimiraglia, R.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Sorensen, S. L.
    Piancastelli, M. N.
    De Fanis, A.
    Okada, K.
    Kitajima, M.
    Tanaka, T.
    Tanaka, H.
    Ueda, K.
    X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance: Experiment and theory2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 6, article id 064304Article in journal (Refereed)
    Abstract [en]

    We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.

  • 12. Ferrighi, Lara
    et al.
    Frediani, Luca
    Cappelli, Chiara
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Helgaker, Trygve
    Ruud, Kenneth
    Density-functional-theory study of the electric-field-induced second harmonic generation (EFISHG) of push-pull phenylpolyenes in solution2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 425, no 4-6, p. 5593-5603Article in journal (Refereed)
    Abstract [en]

    Density-functional theory and the polarizable continuum model have been used to calculate the electric-field-induced second harmonic generation of a series of push-pull phenylpolyenes in chloroform solution. The calculations have been performed using both the Becke 3-parameter Lee-Yang-Parr functional and the recently developed Coulomb-attenuated method functional. Solvation has been investigated by examining the effects of the reaction field, non-equilibrium solvation, geometry relaxation, and cavity field. The inclusion of solvent effects leads to significantly better agreement with experimental observations.

  • 13.
    Gel'mukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Shalagin, A
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    X-ray Raman scattering under pulsed excitation2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 112, no 13, p. 5593-5603Article in journal (Refereed)
    Abstract [en]

    Accounting for actual and anticipated developments in synchrotron radiation- and in x-ray and free electron laser techniques, we present a theory of resonant scattering of short-pulsed x rays. Both the instantaneous and integrated-over-observation-time x-ray scattering spectra are studied. Contrary to the commonly accepted notion of an instantaneous probability, we find that the correct quantity describing the resonant x-ray scattering (RXS) experiment is the probability integrated over the time of measurement. It is shown that the integral RXS probability is given by the convolution of the RXS probability for monochromatic excitation with the Wiener-Khintchine spectrum of the nonstationary incident radiation. We have found that short pulses yield a new spectral band following a non-Raman dispersion law. The finite duration of pulses results in a broadening of the Raman resonance. Some aspects of the theoretical analysis of the RXS spectra as functions of the pulse duration time are analyzed by numerical calculations.

  • 14.
    Gel'mukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Vibrationally resolved core-photoelectron spectroscopy as an infinite-slit interferometry2001In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 64, no 1Article in journal (Refereed)
    Abstract [en]

    During a molecular vibration, an atom changes continuously its position. Just as the emitted photoelectron waves, the electromagnetic waves absorbed by the atom in the different positions are strictly coherent and have different well-defined phases. These phases depend on the relation between the instantaneous internuclear distance and the photoelectron, respectively, photon wavelengths. We predict that the interference of these coherent waves strongly influences the vibrational profile of the photoelectron spectra of core electrons in a molecule. This effect increases with increasing x-ray photon frequency and results in a deformation and broadening of the vibrational profile. In the case of surface adsorbed molecules, the vibrational profile depends strongly on the direction of the photoelectron ejection and photon momentum, and the orientational sensitivity of a vibrational profile can even be used as a tool to define the orientation of adsorbed molecules.

  • 15.
    Gel’mukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Sałek, Paweł
    KTH, Superseded Departments, Biotechnology.
    Privalov, Timofei
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Duration of x-ray Raman scattering1999In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 59, no 1, p. 380-389Article in journal (Refereed)
    Abstract [en]

    There has recently been much interest in using the notion of a duration time to analyze resonant x-ray Raman scattering (RXS) of atoms, molecules, and solids. This notion implies a selection of processes with different time scales responsible for the formation x-ray Raman spectra, and has been useful for actual predictions of various phenomena associated with RXS and that subsequently have been experimentally verified. However, the notion of a duration time for the x-ray scattering event can also have some paradoxical consequences, as when comparing the RXS duration with the relaxation time of the wave packet evolution in the case when the inverse detuning of the excitation energy is shorter than the time of flight or the lifetime of the core excited state. We present here a solution of this contradiction and give a detailed analysis of the notion of the duration time for RXS. It is shown that this time is complex and consists of two qualitatively different contributions. The first originates in the irreversible decay of the core excited state, while the imaginary part is caused by a reversible dephasing in the time domain. We investigate also the evolution of the wave packets of bound and dissociative states to stationary distributions. The theoretical analysis is accompanied by numerical examples of the time evolution of the wave packet in bound and dissociative core excited states of the N2 and HCl molecules.

  • 16.
    Gel'mukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Doppler effects in resonant x-ray Raman scattering1998In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 57, no 4, p. 2511-2526Article in journal (Refereed)
    Abstract [en]

    Theory for Doppler effects in resonant x-ray Raman scattering (RXS) is presented. It is shown that the "electron" Doppler effect is important in nonradiative RXS for decay transitions between continuum nuclear states lying above the dissociation threshold, and that the averaging of the RXS cross section over molecular orientations can lead to strong non-lorentzian broadenings of the atomiclike resonances. The Doppler effect is found to give a unique possibility to distinguish dissociating identical atoms, because different peaks correspond to atoms with opposite Doppler shifts. Spectral features of the atomiclike profile are predicted and analyzed. Strong oscillations of the RXS cross section will occur as a consequence of the interference of the Auger electrons. Due to the Doppler effect and the interference, the atomiclike profile can be associated with supernarrow spectral features, the width of which goes below the lifetime broadening and is practically independent of the spectral distribution of the incident radiation. As another consequence of the oscillations and strong anisotropy caused by the interference, we predict parity selection rules for Auger decay transitions in both bound and dissociative systems. The corresponding experiments can be realized by measurements of resonant Auger of surface adsorbed molecules and for molecules by the electron-ion coincidence technique.

  • 17.
    Helgaker, Trygve
    et al.
    Univ Oslo, Dept Chem, Oslo, Norway..
    Pawlowski, Filip
    Univ Oslo, Dept Chem, Oslo, Norway..
    Reine, Simen
    Univ Oslo, Dept Chem, Oslo, Norway..
    Host, Stinne
    Univ Aarhus, Dept Chem, Aarhus, Denmark..
    Jansik, Branislav
    Univ Aarhus, Dept Chem, Aarhus, Denmark..
    Olsen, Jeppe
    Univ Aarhus, Dept Chem, Aarhus, Denmark..
    Jorgensen, Poul
    Univ Aarhus, Dept Chem, Aarhus, Denmark..
    Coriani, Sonia
    Univ Trieste, Dept Chem, Trieste, Italy..
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Self-consistent field methods applied to large molecular systems2006In: RECENT PROGRESS IN COMPUTATIONAL SCIENCES AND ENGINEERING, VOLS 7A AND 7B / [ed] Simos, T Maroulis, G, VSP BV-C/O BRILL ACAD PUBL , 2006, p. 1297-1297Conference paper (Refereed)
    Abstract [en]

    With recent developments in theory and in implementation, Hartree-Fock and density-functional theory (DFT) self-consistent field (SCF) methods can now be applied to large molecular systems, at a cost that scales linearly with system size. In the present talk, such developments are reviewed, with emphasis on the calculation of energy and molecular properties. In particular, it is demonstrated that energies and molecular properties can now be determined entirely in the atomic orbital (AD) basis, with no implicit or explicit introduction of canonical molecular orbitals in the course of the calculation. After a discussion of energy optimization and convergence of the self-consistent field iterations, some applications are presented, with emphasis on polarizabilities and excitation energies and on the comparison of results obtained by Hartree-Fock and DFT theories in extended systems.

  • 18. Jansik, B.
    et al.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Jonsson, D.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Cubic response functions in time-dependent density functional theory2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 5Article in journal (Refereed)
    Abstract [en]

    We present density-functional theory for time-dependent response functions up to and including cubic response. The working expressions are derived from an explicit exponential parametrization of the density operator and the Ehrenfest principle, alternatively, the quasienergy ansatz. While the theory retains the adiabatic approximation, implying that the time-dependency of the functional is obtained only implicitly-through the time dependence of the density itself rather than through the form of the exchange-correlation functionals-it generalizes previous time-dependent implementations in that arbitrary functionals can be chosen for the perturbed densities (energy derivatives or response functions). In particular, general density functionals beyond the local density approximation can be applied, such as hybrid functionals with exchange correlation at the generalized-gradient approximation level and fractional exact Hartree-Fock exchange. With our implementation the response of the density can always be obtained using the stated density functional, or optionally different functionals can be applied for the unperturbed and perturbed densities, even different functionals for different response order. As illustration we explore the use of various combinations of functionals for applications of nonlinear optical hyperpolarizabilities of a few centrosymmetric systems; molecular nitrogen, benzene, and the C-60 fullerene. Considering that vibrational, solvent, and local field factors effects are left out, we find in general that very good experimental agreement can be obtained for the second dynamic hyperpolarizability of these systems. It is shown that a treatment of the response of the density beyond the local density approximation gives a significant effect. The use of different functional combinations are motivated and discussed, and it is concluded that the choice of higher order kernels can be of similar importance as the choice of the potential which governs the Kohn-Sham orbitals.

  • 19.
    Jansik, Branislav
    et al.
    KTH, Superseded Departments, Biotechnology.
    Jonsson, D.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Calculations of static and dynamic polarizabilities of excited states by means of density functional theory2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 16, p. 7595-7600Article in journal (Refereed)
    Abstract [en]

    We present density functional theory and calculations for excited state second order, static or dynamic, properties. The excited state properties are identified from a double residue of a cubic response function. The performance of various functionals, including the generalized gradient approximation and fractional exact Hartree-Fock exchange, is compared to coupled cluster calculations. Applications on excited state polarizabilities of s-tetrazine and pyrimidine show a good agreement with ab initio correlated, coupled cluster, results.

  • 20. Jonsson, Dan
    et al.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Jansik, Branislav
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Kohn–Sham Time-Dependent Density Functional Theory with Applications to Linear and Nonlinear Properties2006In: Nonlinear optical properties of matter: From molecules to condensed phases / [ed] Manthos G. Papadopoulos, Andrzej J. Sadlej, Jerzy Leszczynski., Springer Netherlands, 2006, p. 151-209Chapter in book (Refereed)
    Abstract [en]

    We review Kohn–Sham density-functional theory for time-dependent response functionsup to and including cubic response. The working expressions are derived from anexplicit exponential parametrization of the density operator and the Ehrenfest principle,alternatively the quasi-energy ansatz. While the theory retains the adiabatic approximation,implying that the time-dependency of the functional is obtained only implicitly—through the time-dependency of the density itself rather than through the form ofthe exchange-correlation functionals—our implementation generalizes previous timedependentapproaches in that arbitrary functionals can be chosen for the perturbed densities(energy derivatives or response functions). Thus, the response of the density canalways be obtained using the stated density functional, or optionally different functionalscan be applied for the unperturbed and perturbed densities, even different functionals fordifferent response order. In particular, general density functionals beyond the local densityapproximation can be applied, such as hybrid functionals with exchange–correlation atthe generalized gradient-approximation level and fractional exact Hartree–Fock exchange.We also review some recent progress in time-dependent density functional theory foropen-shell systems, in particular spin-restricted and spin restricted-unrestricted formalismsfor property calculations. We highlight a sample of applications of the theory

  • 21. Keal, T. W.
    et al.
    Helgaker, T.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Tozer, D. J.
    Choice of exchange-correlation functional for computing NMR indirect spin-spin coupling constants2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 425, no 1-3, p. 163-166Article in journal (Refereed)
    Abstract [en]

    The choice of exchange-correlation functional for the determination of indirect nuclear spin-spin coupling constants in density-functional theory is considered. In an assessment of one-bond (1)J(CH) couplings, the PBE functional was recently shown [S.N. Maximoff, J.E. Peralta, V. Barone, G.E. Scuseria, J. Chem. Theory Comput. 1 (2005) 541] to perform well, significantly outperforming B3LYP. For couplings involving N, 0, and F atoms in simple molecules, we demonstrate that the opposite is observed; PBE is considerably less accurate than B3LYP. By contrast, the B97-2 and B97-3 semi-empirical functionals provide good, consistent quality couplings for all these atom types in an extensive assessment.

  • 22. Kjaergaard, Thomas
    et al.
    Jorgensen, Poul
    Thorvaldsen, Andreas J.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Coriani, Sonia
    Gauge-Origin Independent Formulation and Implementation of Magneto-Optical Activity within Atomic-Orbital-Density Based Hartree-Fock and Kohn-Sham Response Theories2009In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 5, no 8, p. 1997-2020Article, review/survey (Refereed)
    Abstract [en]

    A Lagrangian approach has been used to derive gauge-origin independent expressions for two properties that rationalize magneto-optical activity, namely the Verdet constant V(omega) of the Faraday effect and the B term of magnetic circular dichroism. The approach is expressed in terms of an atomic-orbital density-matrix based formulation of response theory and use London atomic orbitals to parametrize the magnetic field dependence. It yields a computational procedure which is both gauge-origin independent and suitable for linear-scaling at the level of time-dependent Hartree-Fock and density functional theory. The formulation includes a modified preconditioned conjugated gradient algorithm, which projects out the excited state component from the solution to the linear response equation. This is required when solving one of the response equations for the determination of the B term and divergence is encountered if this component is not projected out. Illustrative results are reported for the Verdet constant of H-2, HF, CO, N2O, and CH3CH2CH3 and for the B term of pyrimidine, phosphabenzene, and pyridine. The results are benchmarked against gauge-origin independent CCSD values

  • 23.
    Lian, Ke-Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Jin, Mingxing
    Ding, Dajun
    Density-functional studies of plasmons in small metal clusters2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 17Article in journal (Refereed)
    Abstract [en]

    We study the formation of plasmon modes of small gold clusters by modeling the excitation spectra. The shape change of the longitudinal mode as a function of cluster size is studied using time-dependent Kohn-Sham theory and Gaussian basis sets. The presence of d electrons in gold atoms affect the plasmon formation process, resulting in a high excitation energy for transverse mode and a complicated spectra profile in general. The transverse mode can still be identified with the help of a frozen-orbital approximation.

  • 24. Magnuson, M
    et al.
    Guo, J
    Sathe, C
    Rubensson, E
    Nordgren, J
    Glans, P
    Yang, L
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering1999In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 59, no 6, p. 4281-4287Article in journal (Refereed)
    Abstract [en]

    We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.

  • 25.
    Minaev, Boris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Tunell, Ingvar
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Loboda, Oleksandr
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Singlet-triplet transitions in three-atomic molecules studied by time-dependent MCSCF and density functional theory2004In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 102, no 13, p. 1391-1406Article in journal (Refereed)
    Abstract [en]

    Singlet-triplet transition moments and phosphorescence lifetimes have been calculated for the three-atomic molecules HCN, O-3, H2O, H2S, GeF2, GeCl2 and GeBr2 by time-dependent density functional theory (DFT) utilizing quadratic response functions in order to qualify DFT which recently has become available for studies of this kind [TUNELL, I., RINKEVIVIUS, Z., VAHTRAS, O., SALEK, P., HELGAKER, T., and AGREN, H., 2003, J. chem. phys., 119, 11024]. Comparison with ab initio and experimental data indicates that DFT exhibit results of similar quality as explicitly correlated methods which indicates that it indeed is a viable approach for singlet-triplet transitions. O-3 provides an intriguing example in that a systematic investigation of the singlet-triplet transition moment of its Wulf band indicates a clear advantage of the DFT technique despite the multiconfigurational character of the electronic structure of this molecule. The electronic spin-spin coupling and the hyperfine nuclear coupling constants have also been calculated in order to further characterize the triplet state in the spectra of the investigated systems.

  • 26. Ohta, Koji
    et al.
    Yamada, Satoru
    Kamada, Kenji
    Slepkov, Aaron D.
    Hegmann, Frank A.
    Tykwinski, Rik R.
    Shirtcliff, Laura D.
    Haley, Michael M.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Two-Photon Absorption Properties of Two-Dimensional pi-Conjugated Chromophores: Combined Experimental and Theoretical Study2011In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 2, p. 105-117Article in journal (Refereed)
    Abstract [en]

    The two-photon absorption (TPA) properties of four TPEB [tetrakis(phenylethynyl)benzene] derivatives (TD, para, ortho, and meta) with different donor/acceptor substitution patterns have been investigated experimentally by the femtosecond open-aperture Z-scan method and theoretically by the time-dependent density-functional theory (TDDFT) method. The four compounds show relatively large TPA cross sections, and the all-donor substituted species (TD) displays the largest TPA cross-section sigma((2)) = 520 +/- 30 GM. On the basis of the calculated electronic structure, TD shows no TPA band in the lower energy region of the spectrum because the transition density is concentrated on particular transitions due to the high symmetry of the molecular structure. The centrosymmetric donor-acceptor TPEB para shows excitations resulting from transitions centered on D-pi-D and A-pi-A moieties, as well as transition between the D-pi-D and A-pi-A moieties; this accounts for the broad nature of the TPA bands for this compound. Calculations for two noncentrosymmetric TPEBs (ortho and meta) reveal that the diminished TPA intensities of higher-energy bands result from destructive interference between the dipolar and three-state terms. The molecular orbitals (MOs) of the TPEBs are derivable with linear combinations of the MOs of the two crossing BPEB [bis(phenylethynyl)benzene] derivatives. Overall, the characteristics of the experimental spectra are well-described based on the theoretical analysis.

  • 27. Paterson, M. J.
    et al.
    Christiansen, O.
    Pawlowski, F.
    Jorgensen, P.
    Hattig, C.
    Helgaker, T.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Benchmarking two-photon absorption with CC3 quadratic response theory, and comparison with density-functional response theory2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 5, p. 425-430Article in journal (Refereed)
    Abstract [en]

    We present a detailed study of the effects of electron correlation on two-photon absorption calculated by coupled cluster quadratic response theory. The hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3 has been used to investigate the effects of electron correlation on the two-photon absorption cross sections of formaldehyde (CH2O), diacetylene (C4H2), and water (H2O). In particular, the effects of triple excitations on two-photon transition cross sections are determined for the first time. In addition, we present a detailed comparison of the coupled cluster results with those obtained from Hartree-Fock and density-functional response theories. We have investigated the local-density approximation, the pure Becke-Lee-Yang-Parr (BLYP) functional, the hybrid Becke-3-parameter-Lee-Yang-Parr (B3LYP), and the Coulomb-attenuated B3LYP (CAM-B3LYP) functionals. Our results show that the CAM-B3LYP functional, when used in conjuction with a one-particle basis-set containing diffuse functions, has much promise; however, care must still be exercised for diffuse Rydberg-type states.

  • 28. Peach, M. J. G.
    et al.
    Helgaker, T.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Keal, T. W.
    Lutnaes, O. B.
    Tozer, D. J.
    Handy, N. C.
    Assessment of a Coulomb-attenuated exchange-correlation energy functional2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 8, no 5Article in journal (Refereed)
    Abstract [en]

    The recently proposed CAM-B3LYP exchange-correlation energy functional, based on a partitioning of the r(12)(-1) operator in the exchange interaction into long- and short-range components, is assessed for the determination of molecular thermochemistry, structures, and second order response properties. Rydberg and charge transfer excitation energies and static electronic polarisabilities are notably improved over the standard B3LYP functional; classical reaction barriers also improve. Ionisation potentials, bond lengths, NMR shielding constants and indirect spin-spin coupling constants are comparable with the two functionals. CAM-B3LYP atomisation energies and diatomic harmonic vibrational wavenumbers are less accurate than those of B3LYP. Future research directions are outlined.

  • 29. Peach, Michael J. G.
    et al.
    Tellgrent, Erik I.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Helgaker, Trygve
    Tozer, David J.
    Structural and electronic properties of polyacetylene and polyyne from hybrid and coulomb-attenuated density functionals2007In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 46, p. 11930–11935-Article in journal (Refereed)
    Abstract [en]

    The bond length alternation (BLA), the highest-occupied-lowest-unoccupied (HO-LU) orbital energy gap, and the corresponding excitation energy are determined for trans-polyacetylene (PA) and polyyne (PY) using density functional theory. Results from the Coulomb-attenuated CAM-133LYP functional are compared with those from the conventional BHHLYP and B3LYP hybrid functionals. BLA values and HO-LU gaps are determined using both finite oligomer and infinite chain calculations, subject to periodic boundary conditions. TDDFT excitation energies are determined for the oligomers. The oligomer excitation energies and HO-LU gaps are then used, in conjunction with the infinite chain HO-LU gap, to estimate the infinite chain excitation energy. Overall, BHHLYP and CAM-133LYP give BLA values and excitation energies that are larger and more accurate than those obtained using B3LYP. The results highlight the degree to which excitation energies can be approximated using the HO-LU gaps-at the infinite limit, this approximation works well for B3LYP, but not for the other functionals, where the HO-LU gap is significantly larger. The study provides further evidence for the high-quality theoretical predictions that can be obtained from the CAM-B3LYP functional.

  • 30. Piancastelli, M. N.
    et al.
    Fink, R. F.
    Feifel, R.
    Bassler, M.
    Sorensen, S. L.
    Miron, C.
    Wang, H.
    Hjelte, I.
    Bjorneholm, O.
    Ausmees, A.
    Svensson, S.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Bond-distance-dependent decay probability of the N 1s -> pi* core-excited state in N-22000In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 33, no 9, p. 1819-1826Article in journal (Refereed)
    Abstract [en]

    We report the observation of the unusually weak decay of the N 1s --> pi* core-excited N-2 molecule to the (B) over tilde (2)Sigma(u)(+) final state of N-2(+), which is only detectable in an experiment with high sensitivity. The resonant Auger spectra exhibit an unexpected dependence on the selected vibrational level of the intermediate state. Theoretical calculations show that the interference between direct and resonant photoemission as well as a strong geometry dependence of the decay probability on the bond distance give rise to the observed features.

  • 31. Reine, Simen
    et al.
    Krapp, Andreas
    Iozzi, Maria Francesca
    Bakken, Vebjorn
    Helgaker, Trygve
    Pawlowski, Filip
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    An efficient density-functional-theory force evaluation for large molecular systems2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 4, p. 044102-Article in journal (Refereed)
    Abstract [en]

    An efficient, linear-scaling implementation of Kohn Sham density-functional theory for the calculation of molecular forces for systems containing hundreds of atoms is presented. The density-fitted Coulomb force contribution is calculated in linear time by combining atomic integral screening with the continuous fast multipole method. For higher efficiency and greater simplicity, the near-field Coulomb force contribution is calculated by expanding the solid-harmonic Gaussian basis functions in Hermite rather than Cartesian Gaussians. The efficiency and linear complexity of the molecular-force evaluation is demonstrated by sample calculations and applied to the geometry optimization of a few selected large systems. (C) 2010 American Institute of Physics. [doi:10.1063/1.3459061]

  • 32. Reine, Simen
    et al.
    Tellgren, Erik
    Krapp, Andreas
    Kjaergaard, Thomas
    Helgaker, Trygve
    Jansik, Branislav
    Host, Stinne
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Variational and robust density fitting of four-center two-electron integrals in local metrics2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 10Article in journal (Refereed)
    Abstract [en]

    Density fitting is an important method for speeding up quantum-chemical calculations. Linear-scaling developments in Hartree-Fock and density-functional theories have highlighted the need for linear-scaling density-fitting schemes. In this paper, we present a robust variational density-fitting scheme that allows for solving the fitting equations in local metrics instead of the traditional Coulomb metric, as required for linear scaling. Results of fitting four-center two-electron integrals in the overlap and the attenuated Gaussian damped Coulomb metric are presented, and we conclude that density fitting can be performed in local metrics at little loss of chemical accuracy. We further propose to use this theory in linear-scaling density-fitting developments.

  • 33.
    Rinkevicius, Zilvinas
    et al.
    KTH, Superseded Departments, Biotechnology.
    Telyatnyk, Lydumyla
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Restricted density-functional linear response theory calculations of electronic g-tensors2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 20, p. 10489-10496Article in journal (Refereed)
    Abstract [en]

    A method for calculations of electronic g-tensors based on a spin-restricted open-shell Kohn-Sham formalism and linear response theory is described. Test calculations for main group organic radicals and transition metal compounds have been carried out using two different spin-orbit approximations: Scaled spin-orbit and atomic mean-field spin-orbit operators. The results indicate slightly better performance of the proposed spin-restricted approach compared to previous methods based on the unrestricted Kohn-Sham formalism. An exception to this general improvement are the anions, as they show considerable spin-polarization. The results also show the superiority of the atomic mean field spin-orbit approximation of the spin-orbit operator with respect to the scaled approximation. For main group radicals, quantitative agreement with high level ab initio as well as experimental data are achieved, whereas for transition metal compounds the results systematically underestimate experimental values, showing also a considerable dependency on the employed exchange correlation functional, similarly to previous reports on calculations using unrestricted density functional theory. From this work we conclude that these problems are not primarily associated with the spin-contamination problem, and that they must be referred to the current time-dependent density functional theories as such.

  • 34.
    Rinkevicius, Zilvinas
    et al.
    KTH, Superseded Departments, Biotechnology.
    Tunell, I
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Restricted density functional theory of linear time-dependent properties in open-shell molecules2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 1, p. 34-46Article in journal (Refereed)
    Abstract [en]

    In this paper we report the derivation and the performance of a spin-restricted density functional formalism for linear time-dependent properties in open-shell molecules. The formalism is based on an exponential parameterization of the density operator with the response functions defined through Ehrenfest's principle. In addition to the derivation of formulas, details of implementation are given as well as a discussion of numerical results for excitation energies and dynamic polarizabilities for a selected set of radicals.

  • 35. Rizzo, A.
    et al.
    Cappelli, C.
    Jansik, B.
    Jonsson, D.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Coriani, S.
    Wilson, D. J. D.
    Helgaker, T.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Density-functional theory study of electric and magnetic properties of hexafluorobenzene in the vapor phase2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 23Article in journal (Refereed)
    Abstract [en]

    A series of electric and magnetic properties of hexafluorobenzene have been calculated, including the electric dipole polarizability, magnetizability, electric quadrupole moment, and nonlinear mixed electric dipole-magnetic dipole-electric quadrupole hyperpolarizabilities needed to obtain estimates of the Kerr, Cotton-Mouton, Buckingham, Jones, and magnetoelectric birefringences in the vapor phase. Time-dependent density-functional theory was employed for the calculation of linear-, quadratic, and cubic response functions. A number of density functionals have been considered, along with Sadlej's triple-zeta basis set and the augmented correlation-consistent polarized valence double zeta and augmented correlation-consistent polarized valence triple zeta basis sets. Comparisons have been made with experiment where possible. The analysis of results allows for an assessment of the capability of time-dependent density-functional theory for high-order electromagnetic properties of an electron-rich system such as hexafluorobenzene.

  • 36. Rizzo, A.
    et al.
    Cappelli, C.
    Jansik, Branislav
    KTH, Superseded Departments, Biotechnology.
    Jonsson, D.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Coriani, S.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Density-functional and electron correlated study of five linear birefringences - Kerr, Cotton-Mouton, Buckingham, Jones, and magnetoelectric - in gaseous benzene2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 18, p. 8814-8830Article, review/survey (Refereed)
    Abstract [en]

    We present the results of an extended study of five birefringences-Kerr, Cotton-Mouton, Buckingham, Jones, and Magnetoelectric-on benzene in the gas phase. The relevant molecular quantities-first-order properties, linear, quadratic, and cubic response functions-are computed employing the density-functional theory (DFT) response theory, with a choice of functionals. In some cases, different functionals are employed for the wave-function computational step and for the subsequent analytical response calculation to determine the combination yielding at the same time the optimal energy and energy derivative results. Augmented correlation consistent basis sets of double and triple zeta quality are used. The DFT results are compared to those obtained at the Hartree-Fock level and in some cases within a coupled cluster singles and doubles electronic structure model. The study tries to assess the ability of the DFT response theory to describe a wide range of properties in a system of rather large size and high complexity. The relative strength of the five birefringences for plausible experimental conditions is determined and, when possible, comparison is made with the results of the measurements.

  • 37. Rizzo, A.
    et al.
    Ruud, K.
    Helgaker, T.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Vahtras, Olav
    KTH, Superseded Departments, Biotechnology.
    Sternheimer shieldings and EFG polarizabilities: a density-functional theory study2003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 372, no 04-mar, p. 377-385Article in journal (Refereed)
    Abstract [en]

    The electric field gradient (EFG) at the nucleus, the generalized Sternheimer shielding constants, and the EFG hyperpolarizabilities of a set of reference molecules are computed using analytic density-functional (up to quadratic) response theory. At the three-parameter Becke-Lee-Yang-Parr (B3LYP) level, density functional theory (DFT) underestimates correlation effects compared with other approaches such as coupled-cluster and multiconfigurational self-consistent field. For the prediction of EFG properties of hydrogen nuclei and electron-rich atoms such as halides, DFT/ B3LYP provides results even less reliable than Hartree-Fock theory.

  • 38. Rizzo, Antonio
    et al.
    Cappelli, Chiara
    Jansik, Branislav
    Jonsson, Dan
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Coriani, Sonia
    Agren, Hans
    Wilson, David J. D.
    Helgaker, Trygve
    Junquera-Hernandez, Jose Miguel
    Sanchez de Meras, Alfredo M. J.
    Sanchez-Marin, Jose
    Density-functional study of electric and magnetic properties of hexafluorobenzene in the vapor phase (vol 122, artn no 234314, 2005)2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 3Article in journal (Refereed)
  • 39. Rizzo, Antonio
    et al.
    Cappelli, Chiara
    Jansik, Branislav
    Jonsson, Dan
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Coriani, Sonia
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wilson, David J. D.
    Helgaker, Trygve
    Junquera-Hernandez, Jose Miguel
    Sanchez de Meras, Alfredo M. J.
    Sanchez-Marin, Jose
    A computational study of some electric and magnetic properties of gaseous BF3 and BCl3 (vol 123, artn no 114307, 2005)2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 3Article in journal (Refereed)
  • 40. Rizzo, Antonio
    et al.
    Cappelli, Chiara
    Jansik, Branislav
    Jonsson, Dan
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Coriani, Sonia
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wilson, David J. D.
    Helgaker, Trygve
    Junquera-Hernandez, Jose Miguel
    Sanchez de Meras, Alfredo M. J.
    Sanchez-Marin, Jose
    Density-functional and electron correlated study of five linear birefringences-Kerr, Cotton-Mouton, Buckingham, Jones and magnetoelectric-in gaseous benzene (vol 121, pg 8814, 2004)2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 3Article in journal (Refereed)
  • 41.
    Rubensson, Emanuel H.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    A hierarchic sparse matrix data structure for large-scale Hartree-Fock/Kohn-Sham calculations2007In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 28, no 16, p. 2531-2537Article in journal (Refereed)
    Abstract [en]

    A hierarchic sparse matrix data structure for Hartree-Fock/Kohn-Sham calculations is presented. The data structure makes the implementation of matrix manipulations needed for large systems faster, easier, and more maintainable without loss of performance. Algorithms for symmetric matrix square and inverse Cholesky decomposition within the hierarchic framework are also described. The presented data structure is general; in addition to its use in HartreeFock/Kohn-Sham calculations, it may also be used in other research areas where matrices with similar properties are encountered. The applicability of the data structure to ab initio calculations is shown with help of benchmarks on water droplets and graphene nanoribbons.

  • 42.
    Rubensson, Emanuel H.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Density matrix purification with rigorous error control2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 7Article in journal (Refereed)
    Abstract [en]

    Density matrix purification, although being a powerful tool for linear scaling construction of the density matrix in electronic structure calculations, has been limited by uncontrolled error accumulation. In this article, a strategy for the removal of small matrix elements in density matrix purification is proposed with which the forward error can be rigorously controlled. The total forward error is separated into two parts, the error in eigenvalues and the error in the occupied invariant subspace. We use the concept of canonical angles to measure and control differences between exact and approximate occupied subspaces. We also analyze the conditioning of the density matrix construction problem and propose a method for calculation of interior eigenvalues to be used together with density matrix purification. (C) 2008 American Institute of Physics.

  • 43.
    Rubensson, Emanuel H.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rotations of occupied invariant subspaces in self-consistent field calculations2008In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 49, no 3, p. 032103-Article in journal (Refereed)
    Abstract [en]

    In this article, the self-consistent field (SCF) procedure as used in Hartree-Fock and Kohn-Sham calculations is viewed as a sequence of rotations of the so-called occupied invariant subspace of the potential and density matrices. Computational approximations are characterized as erroneous rotations of this subspace. Differences between subspaces are measured and controlled by the canonical angles between them. With this approach, a first step is taken toward a method where errors from computational approximations are rigorously controlled and threshold values are directly related to the accuracy of the current trial density, thus eliminating the use of ad hoc threshold values. Then, the use of computational resources can be kept down as much as possible without impairment of the SCF convergence. (C) 2008 American Institute of Physics.

  • 44.
    Rubensson, Emanuel H.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Truncation of Small Matrix Elements Based on the Euclidean Norm for Blocked Data Structures2009In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 30, no 6, p. 974-977Article in journal (Refereed)
    Abstract [en]

    Methods for the removal of small symmetric matrix elements based on the Euclidean norm of the error matrix are presented in this article. In large scale Hartree-Fock and Kohn-Sham calculations it is important to be able to enforce matrix sparsity while keeping errors under control. Truncation based on some unitary-invariant norm allows for control of errors in the occupied subspace as described in (Rubensson et al. J Math Phys 49, 032103). The Euclidean norm is unitary-invariant and does not grow intrinsically with system size and is thus suitable for error control in large scale calculations. The presented truncation schemes repetitively use the Lanczos method to compute the Euclidean norms of the error matrix candidates. Ritz value convergence patterns are utilized to reduce the total number of Lanczos iterations.

  • 45.
    Rubensson, Emanuel
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rudberg, Elias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Sparse matrix algebra for quantum modeling of large systems2007In: Applied Parallel Computing - STATE OF THE ART IN SCIENTIFIC COMPUTING     / [ed] Kagstrom B, Elmroth E, Dongarra J, Wasniewski J, Berlin, Germany: Springer-Verlag , 2007, p. 90-99Conference paper (Refereed)
    Abstract [en]

    Matrices appearing in Hartree-Fock or density functional theory coming from discretization with help of atom-centered local basis sets become sparse when the separation between atoms exceeds some system-dependent threshold value. Efficient implementation of sparse matrix algebra is therefore essential in large-scale quantum calculations. We describe a unique combination of algorithms and data representation that provides high performance and strict error control in blocked sparse matrix algebra. This has applications to matrix-rnatrix multiplication, the Trace-Correcting Purification algorithm and the entire self-consistent field calculation.

  • 46.
    Rubensson, Emanuel
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Systematic sparse matrix error control for linear scaling electronic structure calculations2005In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 26, no 15, p. 1628-1637Article in journal (Refereed)
    Abstract [en]

     Efficient truncation criteria used in multiatom blocked sparse matrix operations for ab initio calculations are proposed. As system size increases, so does the need to stay on top of errors and still achieve high performance. A variant of a blocked sparse matrix algebra to achieve strict error control with good performance is proposed. The presented idea is that the condition to drop a certain submatrix should depend not only on the magnitude of that particular submatrix, but also on which other submatrices that are dropped. The decision to remove a certain submatrix is based on the contribution the removal would cause to the error in the chosen norm. We study the effect of an accumulated truncation error in iterative algorithms like trace correcting density matrix purification. One way to reduce the initial exponential growth of this error is presented. The presented error control for a sparse blocked matrix toolbox allows for achieving optimal performance by performing only necessary operations needed to maintain the requested level of accuracy.

  • 47.
    Rubio Pons, Oscar
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Electronic Properties of Ground and Charge Transfer States of p-Substituted-Anilines2005Article in journal (Other academic)
  • 48. Rudberg, E.
    et al.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Helgaker, T.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Calculations of two-photon charge-transfer excitations using Coulomb-attenuated density-functional theory2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 18Article in journal (Refereed)
    Abstract [en]

    In this work, we show that an implementation of Coulomb-attenuated density-functional theory leads to considerably better prospects than hitherto for modeling two-photon absorption cross sections for charge-transfer species. This functional, which corrects for the effect of poor asymptotic dependence of commonly used functionals, essentially brings down the widely different results for larger charge-transfer species between Hartree-Fock and density-functional theory (DFT)-B3LYP into a closer range. The Coulomb-attenuated functional, which retains the best aspects of the Hartree-Fock and DFT-B3LYP methods, proves to be very promising for further modeling design of multiphoton materials with technical applications.

  • 49.
    Rudberg, Elias
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rubensson, Emanuel H.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Automatic Selection of Integral Thresholds by Extrapolation in Coulomb and Exchange Matrix Constructions2009In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 5, no 1, p. 80-85Article in journal (Refereed)
    Abstract [en]

    We present a method to compute Coulomb and exchange matrices with predetermined accuracy as measured by a matrix norm. The computation of these matrices is fundamental in Hartree-Fock and Kohn-Sham electronic structure calculations. We show numerically that, when modern algorithms for Coulomb and exchange matrix evaluation are applied, the Euclidean norm of the error matrix e is related to the threshold value tau as epsilon C tau(alpha). The presented extrapolation method automatically selects the integral thresholds so that the Euclidean norm of the error matrix is at the requested accuracy. This approach is demonstrated for a variety of systems, including protein-like systems, water clusters, and graphene sheets. The proposed method represents an important step toward complete error control throughout the self-consistent field calculation as described in [J. Math. Phys. 2008, 49, 032103].

  • 50.
    Rudberg, Elias
    et al.
    KTH, School of Biotechnology (BIO).
    Rubensson, Emanuel H.
    KTH, School of Biotechnology (BIO).
    Salek, Pawel
    KTH, School of Biotechnology (BIO).
    Estimation of errors in Coulomb and exchange matrix constructionManuscript (Other academic)
12 1 - 50 of 82
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