Trygve Helgaker


Born August 11, 1953 in Porsgrunn, Norway.

Professor of Chemistry, Department of Chemistry, University of Oslo, Norway.
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Member of the Royal Swedish Academy of Sciences (2021), Fridtjov Nansen Award for Excellence in Science of Norwegian Academy of Science and Letters (2019), Ede Kapuy Memorial Lecture (2016), Molecular Physics Festschrift (2013), Award for Outstanding Research (Møbius Prize) of the Research Council of Norway (2011), Research Excellence Award, ICCMSE (2010), ERC Advanced Grant (2010), Centenary Prize of the Royal Society of Chemistry (2007), Guldberg–Waage Medal of the Norwegian Chemical Society (2007), University of Oslo Research Prize (2006), Member of IAQMS (2005), Board member, WATOC (2005), Member of Norwegian Academy of Science and Letters (2004), Charles A. Coulson Lecture (1999), Odd Hassel Scholarship of the Norwegian Research Council for Science and Humanities (1989), Fridtjof Nansen's Award for Young Scientists (1985)

Author of:

More than 340 scientific papers, “Molecular Electronic-Structure Theory” (Wiley, Chichester, 2000), with Poul Jørgensen and Jeppe Olsen. One of the principal developers of the Dalton program package.

Important Contributions:

  • The development of second-quantization theory for the calculation of response functions with perturbation-dependent basis functions. Its implementation and application to geometrical and magnetic molecular properties, including NMR parameters.
  • The introduction of the variational Lagrangian method for the calculation of molecular properties for nonvariational wave functions in the same manner as for variational wave functions with the wave-function parameters obeying the 2n+1 rule and their multipliers the 2n+2 rule.
  • The development of the integral-direct coupled-cluster method. Its application to the study of the basis-set convergence of orbital-based correlated methods; the establishment of the principal orbital expansion and the two-point extrapolation technique, reducing basis-set errors by an order of magnitude, thereby making standard, orbital-based calculations competitive with explicitly correlated ones.
  • The accurate and systematic benchmarking of quantum chemistry, including the rigorous calculation of atomization energies and spectroscopic constants to within the errors imposed by the Schrödinger equation.
  • The introduction of ab initio direct dynamics for integrating the classical Born–Oppenheimer trajectories on the fly, without constructing the potential energy surface in advance, with several applications using multiconfigurational self-consistent field theory.
  • The study of fundamentals in DFT including the introduction of Moreau–Yosida regularization, the application of Lieb variation principle to molecular systems, and the development of current-density functional theory (CDFT) in a magnetic field
  • Ths study of chemistry in ultrastrong magnetic fields and the discovery of perpendicular paramagentic bonding (2012). Development and implementation of molecular dynamics in a magnetic field with inclusion of the Lorentz force.