[1] His interest in Theoretical and Computational Chemistry was raised during a course held by Werner Fischer and firmly established by attending a Summer School organised by Per-Olov Löwdin in 1960 at Uppsala University.

[6] With one of them, Tokuei Sako (Nihon University, Campus Funabashi, Chiba), he was connected for many years after his retirement by a close, successful cooperation.

As visiting scientist he has spent one year each at the IBM Research Laboratories in San Jose, California, and at the Harvard College Observatory in Cambridge, Massachusetts, and six months at the Hokkaido University in Sapporo.

Within the framework of his scientific cooperations he has visited repeatedly up to several month partner institutions, among others in Brasil, Chile, Canada, Great Britain, India, Japan, Poland, Sweden, the Slovak Republic, Venezuela, Uruguay and the USA.

In 1969 he started, jointly with Alain Veillard (University of Strasbourg), the tri-annual Series of European Seminars on Computational Methods in Quantum Chemistry.

The research activities of Geerd Diercksen have been focused on the development and implementation of ab-initio methods and their application to the accurate and reliable calculation of the properties of few electron systems.

Jointly with Wolfgang Kraemer (MPA) and Björn Roos (Lund University) he was the first to calculate the electron correlation energy of the hydrogen bond in the water dimer.

The study of impact cross sections has required the time-consuming calculation of potential energy hypersurfaces most often sampling more than 100 points of support.