Trygve Helgaker  Trygve Helgaker (born August 11, 1953 in Porsgrunn, Norway) is professor of chemistry, Department of Chemistry, University of Oslo, Norway. He is a member of the International Academy of Quantum Molecular Science, 2005. He has written more than 200 scientific papers, and the book, "Molecular Electronic-Structure Theory" (Trygve Helgaker, Poul Jørgensen, and Jeppe Olsen, Wiley, Chichester, 2000). He is one of the main authors of the DALTON program.