Yngve Öhrn, Scientist, Leader, and Friend

Jan Linderberg    Department of Chemistry Aarhus University DK-8000 Aarhus C, Denmark

1 PREAMBLE

Bergslagen, the Swedish mining district, covers part of Värmland, Dalarna, Västmanland, and Uppland. Copper was mined at Falun since the thirteenth century, silver at Sala, and iron was plentiful and of good metallurgical quality at numerous places. It was the backbone for an economy that allowed Swedish kings to implement an expansive international policy in the seventeenth century and for a technological and scientific development with prominent results in engineering and natural sciences with people such as Swedenborg, Linné, Polhem, Scheele, and Bergman making pioneering discoveries. Jöns Jacob Berzelius and his students discovered and characterized a number of elements in the minerals from this region. Berzelius initiated the classification, in the spirit of Linné’s sexual system for the flora, of chemical elements that led to Mendelejev’s periodic system and he rose to become a most influential chemist in the first half of the nineteenth century.

Mining and iron extraction through blast-furnaces based on charcoal from the extensive forests became a major occupation in Bergslagen in the seventeenth century when most farmers had a share of a mine and a furnace. Development of the technical use of the iron was accelerated by foreign blacksmiths, principally from the Walloon part in present day Belgium, and there grew a population of skilled and respected members of the many villages and towns of the region. Knowledge of the processes involved in steel manufacturing developed mainly as an intellectual capital in the people occupied in the production, there was little instrumentation to tell about composition and temperature during the operation.

Traditions and societal structures from the emerging Swedish steel industry were still very much present in the first half of this century. Yngve Öhrn was born in 1934 as the son of Nils and Elsa Öhrn at Avesta in the heart of Bergslagen. Nils had his occupation in the steel rolling mill in a town dominated by the Avesta Järnverk, one of several exponents of the Swedish “bruks”-tradition (1) that had grown out of the original farmer shared operations. Respect for knowledge and skills was still manifest and schooling was encouraged at all levels. The low birth rate in Sweden in the 1930’s (2) gave incentive to government initiatives in the realm of education as well as in other fields. A concept of an “intellectual reserve” was established to promote further education throughout the Swedish population.

Sports activities was a significant part of the social life in the growing industrial towns, track and field, football (soccer), cross country skiing and bandy, a team sport on ice with a small light ball and hooked sticks, were in the focus of attention and rivalry between towns. Yngve Öhrn showed his prowess in school and in track and field, he earned a baccalaureate from Avesta Gymnasium with high grades and a relay championship in 4 × 100 m at the national school track meet.

Military service was mandatory for able as well as some not so able male Swedes and Yngve Öhrn subscribed to reserve officer’s training in the signal corps. He served a first installment of fifteen months, then started studies in mathematics at Uppsala University. This was followed by physics and theoretical physics while he took summers off to complete the military training as an ensign. He married Ann in August 1957 and completed the undergraduate studies with a master’s degree, well within the standard allotted time and by 1958 he was looking into the options for graduate studies.

Per-Olov Löwdin established the Uppsala Quantum Chemistry Group in 1956 and acquired the first of a series of contracts with the Aerospace Research Laboratories, OAR, through the European Office of Aerospace Research, United States Air Force. This funding extended substantially the base provided by the King Gustaf VI Adolfs 70-Years fund for Swedish Culture and the Knut and Alice Wallenberg’s Foundation and Löwdin could offer opportunities for several students to pursue research and studies towards graduate degrees. Yngve Öhrn learned about this possibility through his friend Jan Nordling, who had joined the effort in connection with the acquisition by the Group of the first electronic computer at Uppsala University in late 1957. He approached Löwdin and was quickly introduced to the rather special and quite international ambiance of “research in Atomic, Molecular and Solid State Theory”. Thus I, who had joined Löwdin in 1957, got to know, respect, and earn the friendship of Yngve Öhrn.

Graduate studies in quantum chemistry at Uppsala in the late fifties were not formally recognized by the authorities of the University. The Quantum Chemistry Group was associated with the University but was to a large degree autonomous, having for instance its own fiscal arrangements with granting agencies. Löwdin’s position as an employee of the research council gave no rights of examination or degree granting privileges. It was indicated that a solution to this calamity might be forthcoming, possibly by an American option. Löwdin was negotiating with institutions “over there” about a cooperative project. This came into being in 1960 when the University of Florida invited Löwdin to establish the Quantum Theory Project as a joint effort between the departments of chemistry and physics. The same year he ascended to the new chair of quantum chemistry at Uppsala whereby the field of study was recognized and the privileges of curriculum definition and examination were established for the new Department of Quantum Chemistry. We could then strive for the degree of filosofie licentiat in quantum chemistry. A doctorate required that the candidate had the fil. lic., a published thesis, which could be either a summary of published papers or a monograph and which was submitted to the university library in some 300 copies, and that some further formalities by the college were observed. The successful defense of the thesis in a public ceremony against an opponent appointed by the college was also required. The right to teach, jus docendi, at the University was bestowed on the candidate who passed with honors. No remuneration followed the title of docent.

Florida appeared to fledgling Swedish scientists to be an exciting place and quite a few of us were given the opportunity for an extended stay in Gainesville with the Quantum Theory Project (3). My first sojourn there was from May 1960 to May 1961. Yngve Öhrn and his family arrived in March 1961. Yngve had then gotten well into the project of electronic correlation in small atoms and while we had struck up a friendship from his first day with the Uppsala group we had not been engaged in the same project. Both of us felt that we could benefit from a closer collaboration. Our outlooks on the field of quantum chemistry, on society, sports, and family were kindred and it was anticipated that we should get on to a common project eventually.

Formal structures for the acquisition of academic degrees in quantum chemistry were established in the year following Löwdin’s appointment to the chair in May 1960. Anders Fröman became the first to earn the fil. lic. degree in December 1961 and thus started the “institutionalization” of the field. It had until then a flavor of novelty and exclusivity which was embraced by some and repelled others. The new status changed the prerequisites for graduate studies as well, undergraduate chemistry as well as experimental physics should now be a part of the baggage of new students.

Yngve Öhrn returned to Uppsala in May 1963 after nearly two years at Gainesville and a month with Hirschfelder’s group at Wisconsin. His work with Jan Nordling on the awkward integrals for three electron wave functions with interparticle coordinates was published (4) and was the basis for his fil. lic. degree, which is translated as equivalent to the Ph. D. from a U. S. academic institution. Yngve and I initiated our long and close collaboration during the academic year 1963-64. The last paper for my doctorate was submitted in late February 1964 and then we had started a project with Anders Fröman on “Penetration Effects in the 2 F-Series of Cs I” (5) which gave a reasonable description of the quantum defects determined by Kjell Bockasten.

2 PROPAGATORS

Yngve Öhrn’s research profile added an essential element in early 1964. A paper of lasting influence in theoretical chemistry and physics was published by John Hubbard in the November 26, 1963 issue of the Proceedings of the Royal Society (6). The model carrying the author’s name was defined and a particular approximation was introduced in the hierarchy of equations for the one-particle Green function. Obvious formal similarities relate Hubbard’s model hamiltonian with the prominently featured Pariser-Parr-Pople formalism (7) as extensions of the tight-binding schemes by Hückel (8) for conjugated hydrocarbons and Bloch (9) for crystalline systems. The Green function usage tied in with the elegant work...