Trygve Helgaker was born on August 11 1953 in Porsgrunn, Norway. He received the degree of cand. scient. in chemistry in 1980 and the degree of dr. philos. in 1986, both at the University of Oslo. After postdoctoral positions at the Institute for Mathematics and its Applications (IMA), University of Minnesota in 1986–87 and at the Department of Chemistry, Aarhus University in 1987–89, Helgaker became an associate professor (førsteamanuensis) at the Department of Chemistry, University of Oslo in 1989, where he became a full professor in 1993.
Helgaker was on sabbatical leave in the group of Prof. Nicholas Handy at the University of Cambridge in 1999–2000 and in the group of Prof. David Tozer at Durham University in 2006–07. In January 2003, Helgaker a was a guest professor at Faculté de Chimie, Université Louis Pasteur in Strasbourg. Since 2007, Helgaker has been co-director of the Centre for Theoretical and Computational Chemistry (CTCC), a Centre of Excellence awarded by the Research Council of Norway 2007–2017.
Trygve Helgaker has been working on a wide variety of topics in the domain of quantum chemistry, making several seminal contributions to the development of the field. He has been particularly active in the development of analytic methods for calculating molecular responses to geometrical or magnetic perturbations for correlated wave functions and density functional theory, utilizing his expertise in molecular integral evaluations. This also allowed him to develop the first approach to ab initio direct dynamics based on an on-the-fly evaluation of the forces acting on a molecule on the potential energy surface. In recent years, he has extended his work on molecular integral evaluations to provide new approaches for achieving linear scaling in self-consistent-field calculations as well as presented new and efficient approaches to the evaluation of higher-order geometrical derivatives of two-electron repulsion integrals.
A seminal contribution to the development of analytic methods for correlated wave functions was the introduction of the Lagrangian approach for non-variational wave functions, allowing for a very elegant and convenient way of deriving the working equations for correlated methods such as MP2 and coupled-cluster theory. Through this methodology, Helgaker has also made important contributions to the field of high-accuracy methods based on R12 methodology or based on basis-set extrapolation techniques, and his work on these basis-set extrapolation schemes are among his most cited papers.
His interest in magnetic properties is reflected in a large number of studies of in particular nuclear magnetic resonance parameters and the computational requirements needed for their accurate theoretical evaluation. After a sabbatical with Nicholas Handy, Helgaker also got involved in density functional theory, where he has had a particular interest in the use of the Lieb variational principle for DFT. He has also extended the use of density-functional theory a large number of higher-order molecular responses, making DFT today the method of choice for studies of nonlinear optical processes such as two-photon absorption.
Since the 1980s, Trygve Helgaker has developed the quantum-chemistry program system Dalton in cooperation with other researchers in Scandinavia. Dalton has been licensed to almost 2000 research groups worldwide and is one the most flexible program systems in quantum chemistry.
Helgaker has published 257 ISI-registered articles, which have been cited more than 13000 times. He is Norway's most cited chemist and has an H-index of 60. With Poul Jørgensen and Jeppe Olsen from the Department of Chemistry, Aarhus University, Helgaker has published a 1000-page monograph Molecular Electronic-Structure Theory (Wiley, Chichster, 2000), which has been cited more than 800 times.
Helgaker has also translated Russian fiction to Norwegian: Leo Tolstoy, Om vold og kjærlighet (Solum, Oslo, 1977) and Boris Pilnyak, Armesjefens død, in Moderne russiske fortellere, ed. G. Kjetsaa (Aschehoug, Oslo, 1977).
Awards and honours
Helgaker has received a number of awards and honours. He is an elected member of the Norwegian Academy of Science and Letters (2004), the International Academy of Quantum Molecular Sciences (2005) and the WATOC Scientific Board (2005). He received in 2006 the University of Oslo Research Excellence award, the Guldberg-Waage medal from the Norwegian Chemical Society in 2007, the Centenary Lectureship and Medal of the Royal Society of Chemistry,and in 2011 the award for outstanding research (Møbius award) from the Research Council of Norway. In 2011, he was also awarded an Advanced Grant from the European Research Council (ERC) for the ABACUS project.
Teaching and summer schools
Helgaker is a highly regarded teacher and lecturer. He received in 1992 "Den Gyldne Spatel" teaching award from the students at the Department of Chemistry, University of Oslo. Together with Poul Jørgensen and Jeppe Olsen at Aarhus University, Helgaker has biennially since 1990 organized the Sostrup Summer School: Quantum Chemistry and Molecular Properties. Since 1991, Helgaker has been a lecturer at the European Summer School in Quantum Chemistry (ESQC), held biennially near Palermo in Sicily.