Browsing Kjemisk institutt by Author "Helgaker, Trygve"

Now showing items 1-20 of 25

  • A quantum-mechanical non-Born–Oppenheimer model of a molecule in a strong magnetic field 
    Adamowicz, Ludwik; Stanke, Monika; Tellgren, Erik; Helgaker, Trygve (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2020)
    Interactions of a stationary external magnetic field with the spin and orbital magnetic momenta of a molecule are included in the quantum mechanical model where the Born–Oppenheimer approximation is not assumed. The model ...
  • Ab initio molecular dynamics with screened Lorentz forces. I. Calculation and atomic charge interpretation of Berry curvature 
    Culpitt, Tanner Phillip; Peters, Laurens; Tellgren, Erik Ingemar; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2021)
    The dynamics of a molecule in a magnetic field is significantly different from its zero-field counterpart. One important difference in the presence of a field is the Lorentz force acting on the nuclei, which can be decomposed ...
  • Analytic calculation of the Berry curvature and diagonal Born-Oppenheimer correction for molecular systems in uniform magnetic fields 
    Culpitt, Tanner Phillip; Peters, Laurens; Tellgren, Erik Ingemar; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2022)
    The diagonal nonadiabatic term arising from the Born–Oppenheimer wave function ansatz contains contributions from a vector and scalar potential. The former is provably zero when the wave function can be taken to be real ...
  • Analytic cubic and quartic force fields using density-functional theory 
    Ringholm, Magnus; Jonsson, Dan Johan; Bast, Radovan; Gao, Bin; Thorvaldsen, Andreas johan; Ekstrøm, Ulf; Helgaker, Trygve; Ruud, Kenneth (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)
    We present the first analytic implementation of cubic and quartic force constants at the level of Kohn–Sham density-functional theory. The implementation is based on an open-ended formalism for the evaluation of energy ...
  • Berry population analysis: Atomic charges from the Berry curvature in a magnetic field 
    Peters, Laurens; Culpitt, Tanner Phillip; Tellgren, Erik Ingemar; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2023)
    The Berry curvature is essential in Born–Oppenheimer molecular dynamics, describing the screening of the nuclei by the electrons in a magnetic field. Parts of the Berry curvature can be understood as the external magnetic ...
  • Calculating excitation energies by extrapolation along adiabatic connections 
    Rebolini, Elisa; Toulouse, Julien; Teale, Andrew Michael; Helgaker, Trygve; Savin, A (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    In this paper, an alternative method to range-separated linear-response time-dependent density-functional theory and perturbation theory is proposed to improve the estimation of the energies of a physical system from the ...
  • Choice of basic variables in current-density-functional theory 
    Tellgren, Erik; Kvaal, Simen; Sagvolden, Espen; Ekström, Ulf Egil; Teale, Andrew Michael; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2012)
    The selection of basic variables in current-density-functional theory and formal properties of the resulting formulations are critically examined. Focus is placed on the extent to which the Hohenberg-Kohn theorem, ...
  • Connections between variation principles at the interface of wave-function and density-functional theories 
    Irons, Tom J P; Furness, James W.; Ryley, Matthew S.; Zemen, Jan; Helgaker, Trygve; Teale, Andrew Michael (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)
    A recently proposed variation principle [N. I. Gidopoulos, Phys. Rev. A 83, 040502(R) (2011)] for the determination of Kohn–Sham effective potentials is examined and extended to arbitrary electron-interaction strengths and ...
  • Dalton Project: A Python platform for molecular- and electronic-structure simulations of complex systems 
    Olsen, Jógvan Magnus Haugaard; Reine, Simen Sommerfelt; Vahtras, Olav; Kjellgren, Erik; Reinholdt, Peter; Dundas, Karen O.H; Li, Xin; Cukras, Janusz; Ringholm, Magnus; Hedegård, Erik Donovan; Di Remigio, Roberto; List, Nanna H.; Faber, Rasmus; Tenorio, Bruno Nunes Cabral; Bast, Radovan; Pedersen, Thomas Bondo; Rinkevicius, Zilvinas; Sauer, Stephan P. A.; Mikkelsen, Kurt V.; Kongsted, Jacob; Coriani, Sonia; Ruud, Kenneth; Helgaker, Trygve; Jensen, Hans Jørgen Aa.; Norman, Patrick (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2020)
    The Dalton Project provides a uniform platform access to the underlying full-fledged quantum chemistry codes Dalton and LSDalton as well as the PyFraME package for automatized fragmentation and parameterization of complex ...
  • DFT exchange: sharing perspectives on the workhorse of quantum chemistry and materials science 
    Teale, Andrew Michael; Helgaker, Trygve; Savin, Andreas; Adamo, Carlo; Aradi, Balint; Arbuznikov, Alexei V.; Ayers, Paul W.; Baerends, Evert Jan; Barone, Vincenzo; Calaminici, Patrizia; Cances, Eric; Carter, Emily A.; Chattaraj, Pratim Kumar; Chermette, Henry; Ciofini, Ilaria; Crawford, T. Daniel; de Proft, Frank; Dobson, John F.; Draxl, Claudia; Frauenheim, Thomas; Fromager, Emmanuel; Fuentealba, Patricio; Gagliardi, Laura; Galli, Giulia; Gao, Jaili; Geerlings, Paul; Gidopoulos, Nikitas I.; Gill, Peter M. W.; Gori-Giorgi, Paola; Görling, Andreas; Gould, Tim; Grimme, Stefan; Gritsenko, Oleg; Jensen, Hans Jørgen Aagaard; Johnson, Erin R.; Jones, Robert O.; Kaupp, Martin; Köster, Andreas M.; Kronik, Leeor; Krylov, Anna I.; Kvaal, Simen; Laestadius, Andre; Levy, Mel; Lewin, Mathieu; Liu, Shubin; Loos, Pierre-Francois; Maitra, Neepa T.; Neese, Frank; Perdew, John P.; Pernal, Katarzyna; Pernot, Pascal; Piecuch, Piotr; Rebolini, Elisa; Reining, Lucia; Romaniello, Pina; Ruzsinszky, Adrienn; Salahub, Dennis R.; Scheffler, Matthias; Schwerdtfeger, Peter; Staroverov, Viktor N.; Sun, Jianwei; Tellgren, Erik Ingemar; Tozer, David J.; Trickey, Samuel B.; Ullrich, Carsten A.; Vela, Alberto; Vignale, Giovanni; Wesolowski, Tomasz A.; Xu, Xin; Yang, Weitao (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2022)
    In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method ...
  • Exchange-only virial relation from the adiabatic connection 
    Laestadius, Andre; Csirik, Mihaly Andras; Penz, Markus; Tancogne-Dejean, Nicolas; Ruggenthaler, Michael; Rubio, Angel; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2024)
    The exchange-only virial relation due to Levy and Perdew is revisited. Invoking the adiabatic connection, we introduce the exchange energy in terms of the right-derivative of the universal density functional w.r.t. the ...
  • Fermion N -representability for prescribed density and paramagnetic current density 
    Tellgren, Erik; Kvaal, Simen; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)
    The N-representability problem is the problem of determining whether there exists N-particle states with some prescribed property. Here we report an affirmative solution to the fermion N-representability problem when both ...
  • First-Principles Calculation of 1H NMR Chemical Shifts of Complex Metal Polyhydrides: The Essential Inclusion of Relativity and Dynamics 
    Castro, Abril C; Balcells, David; Repisky, Michal; Helgaker, Trygve; Cascella, Michele (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2020)
    1H NMR spectroscopy has become an important technique for the characterization of transition-metal hydride complexes, whose metal-bound hydrides are often difficult to locate by X-ray diffraction. In this regard, the ...
  • Four-component relativistic 31P NMR calculations for: Trans -platinum(ii) complexes: Importance of the solvent and dynamics in spectral simulations 
    Castro, Abril C.; Fliegl, Heike; Cascella, Michele; Helgaker, Trygve; Repisky, Michal; Komorovsky, Stanislav; Medrano, María Ángeles; Quiroga, Adoración G.; Swart, Marcel (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2019)
    We report a combined experimental–theoretical study on the 31P NMR chemical shift for a number of trans-platinum(II) complexes. Validity and reliability of the 31P NMR chemical shift calculations are examined by comparing ...
  • Generalized Kohn-Sham iteration on Banach spaces 
    Laestadius, Andre; Penz, Markus; Tellgren, Erik; Ruggenthaler, Michael; Kvaal, Simen; Helgaker, Trygve (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2018)
    A detailed account of the Kohn–Sham (KS) algorithm from quantum chemistry, formulated rigorously in the very general setting of convex analysis on Banach spaces, is given here. Starting from a Levy–Lieb-type functional, ...
  • Lower Semicontinuity of the Universal Functional in Paramagnetic Current-Density Functional Theory 
    Kvaal, Simen; Laestadius, Andre; Tellgren, Erik Ingemar; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2021)
    A cornerstone of current–density functional theory (CDFT) in its paramagnetic formulation is proven. After a brief outline of the mathematical structure of CDFT, the lower semicontinuity and expectation-valuedness of the ...
  • Magnetic-Field Density-Functional Theory (BDFT): Lessons from the Adiabatic Connection 
    Reimann, Sarah; Borgoo, Alex; Tellgren, Erik; Teale, Andrew Michael; Helgaker, Trygve (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2017)
    We study the effects of magnetic fields in the context of magnetic field density-functional theory (BDFT), where the energy is a functional of the electron density ρ and the magnetic field B. We show that this approach is ...
  • Magnetic-translational sum rule and approximate models of the molecular Berry curvature 
    Peters, Laurens; Culpitt, Tanner Phillip; Tellgren, Erik Ingemar; Helgaker, Trygve (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2022)
    The Berry connection and curvature are key components of electronic structure calculations for atoms and molecules in magnetic fields. They ensure the correct translational behavior of the effective nuclear Hamiltonian and ...
  • Molecular dynamics of linear molecules in strong magnetic fields 
    Monzel, Laurenz; Pausch, Ansgar; Peters, Laurens; Tellgren, Erik Ingemar; Helgaker, Trygve; Klopper, Wim (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2022)
    Molecular rotations and vibrations have been extensively studied by chemists for decades, both experimentally using spectroscopic methods and theoretically with the help of quantum chemistry. However, the theoretical ...
  • Molecular vibrations in the presence of velocity-dependent forces 
    Tellgren, Erik Ingemar; Culpitt, Tanner Phillip; Peters, Laurens; Helgaker, Trygve (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2023)
    A semiclassical theory of small oscillations is developed for nuclei that are subject to velocity-dependent forces in addition to the usual interatomic forces. When the velocity-dependent forces are due to a strong magnetic ...