This issue of Molecular Physics is dedicated to, and celebrates the research achievements of, Professor Hans-Joachim Werner, Director of the Institute for Theoretical Chemistry, Universität Stuttgart, Germany.
Hans-Joachim Werner was born in Hamburg, West Germany, on 16 April 1950, and was brought up in Königstein, near Frankfurt-am-Main. He began studying chemistry at the Johannes Gutenberg University, Mainz in 1969, completing his Diploma in 1975. His Diploma research project, supervised by Wilfried Meyer, produced probably the first accurate computations of electric dipole polarisabilities of atoms and diatomic molecules. At this time, the group of Meyer, which also included Pavel Rosmus and Peter Botschwina, was demonstrating the power of first-principles electronic structure computations to provide accurate predictions of molecular properties, provided that one used appropriate methodology for including electron correlation effects properly (in their case, at that time, the Coupled Electron Pair Approximation with large orbital basis sets). Their calculations were also made possible on the modest computing resources available at that time by the use of pair natural orbitals, an early precursor of the development of local correlation methodology.
He moved to Göttingen for his PhD in the group of Albert Weller, and alongside Klaus Schulten, in the area of radical–radical recombination kinetics, and their application to biological photochemical processes, receiving his PhD degree in 1977.
In 1977, he returned both to Frankfurt and to the field of molecular electronic structure computation. A collaboration with Pavel Rosmus, that ultimately resulted in 62 joint papers across 30 years, continued to establish high-accuracy results for spectroscopic properties of small molecules. It was at this time that he embarked on the development of multiconfigurational methods for the treatment of excited states and breaking chemical bonds. Publications with Wilfried Meyer showed how it was possible to achieve a reliably convergent algorithm for the multiconfigurational self-consistent field (MCSCF) ansatz, and how the MCSCF method could be applied successfully to problems where diabatic potential energy surfaces cross. He then began to pursue Wilfried Meyer's proposal for internally-contracted wavefunctions to introduce dynamic correlation effects starting from MCSCF, producing, with Ernst-Albrecht Reinsch, a first multireference configuration interaction (MRCI) computer program. After receiving his Habilitation in 1982, he took up a position with Meyer in Kaiserslautern. In 1983, he was a Guest Scientist at Los Alamos National Laboratory, where he was able to exploit one of the first Cray-1 supercomputers.
He spent a year (1984–1985) as visiting Research Fellow at Churchill College, Cambridge. During this period, he interacted with the group of Nicholas Handy, in particular Peter Knowles, on numerical algorithms for MCSCF. On returning to a Heisenberg Fellowship at Frankfurt, his research developed towards the use of potential energy surfaces to understand chemical dynamics. Around this time, he established a collaboration with Millard Alexander, initially focused on the inelastic scattering of rare-gas atoms and electronically degenerate or excited molecules.
From 1986 onwards, in collaboration with Peter Knowles, he worked further on the internally-contracted MRCI method. This period marked the emergence of the Molpro code as a fully functional integrated electronic structure code, although its roots can be traced back, through the precursor MCSCF and SCEP programs, to the programs developed by Peter Pulay and Wilfried Meyer in the 1960s. Apart from direct collaborations with its authors, Molpro was first distributed in 1991, and nowadays has users at more than 500 sites in academia and industry.
In 1987, he was appointed Full Professor at Universität Bielefeld. During the subsequent years he pursued ground-breaking highly accurate, complete first-principles calculations of the dynamics of chemical reactions and energy-transfer processes, including the use of MRCI for potential-energy, spin-orbit, and non-adiabatic coupling surfaces, and explicit quantum dynamics. The premier example of this work is the reaction F + H2 → FH + H, for which the generation of very accurate potential energy surfaces has had a profound effect on the understanding of chemical dynamics, and has influenced the course and understanding of a number of important experimental investigations.
Principally during the 1990s, he contributed significantly to the development of methods that calculate and use the gradient of the potential energy surface, including gradient codes for frozen-core and excited state MCSCF, multireference perturbation theory, and MP2 and coupled-cluster theory, together with geometry optimisation, vibrational frequencies and reaction-path following methods. His work in this area, including the application of density fitting (since 2002), has been done in collaboration with Martin Schütz, Roland Lindh, Guntram Rauhut and Fred Manby.
From 1992, he began to work on electronic structure methods suitable for use where Hartree-Fock is dominant, focusing initially on closed-shell and open-shell coupled cluster methods. This research project developed by adopting and extending the local correlation ansatz proposed originally by Pulay, and has had very significant impact in recent years. The size range of molecules amenable to accurate quantum mechanics has been extended dramatically through low-order scaling methods based on locality. More recently, i.e. from 2005 onwards, he has been a leader in the introduction of complementary ‘F12’ methods that introduce explicit correlation and eliminate the orbital basis problem. These strands of his activity have benefited significantly from collaboration with Martin Schütz, Fred Manby and others.
Since 1994, he has been Director of the Institute for Theoretical Chemistry of Universität Stuttgart, serving also in recent years as Dekan. Scientific interactions have been enriched through his active promotion of cooperative networks, including three European Community research training networks, and annual ski seminars with the groups of Wim Klopper, Jürgen Gauss and others. He has also served the research community through editorship of Molecular Physics and other journals, and service to the Deutsche Forschungsgemeinschaft and within the board of the German-speaking Theoretical Chemists. His achievements have been recognised through prestigious awards that include the membership of the International Academy of Quantum Molecular Sciences, and the Max Planck and Gottfried Wilhelm Leibniz awards.
Many of Hans-Joachim Werner's significant collaborations have been long-lived, and those of us who have been fortunate to be involved in them have enjoyed the friendship and cooperation that has been a wonderful scientific and personal enrichment. This issue celebrates his 60th birthday through the work of his friends and colleagues, and we look forward to many more years of scientific achievement.