Björn Olof Roos (1937–2010)

Abstract

Björn Roos was one of the most prominent theoretical chemists of the 20th and early 21st century. His membership in the International Academy of Quantum Molecular Sciences (IAQMS) honored perhaps more the IAQMS than it honored Björn Roos himself. Also, he was an active member of the Bureau of that Academy, in addition to important positions of trust in Sweden. Björn was a Ph.D. student of Inga Fischer-Hjalmars, who in turn had studied with Charles Coulson. It is interesting to ask whether his combination of intellectual rigor and sense for the physical and chemical facts can be partially derived from his academic ancestry. He started with semiempirical methods but switched to ab initio method development in 1968. After only a few years, in 1972, he had his first permanent achievement, the direct Configuration Interaction (CI) method. The Complete Active Space method followed in 1980 and CASPT2 in 1990. His scientific oeuvre is discussed by others in this volume. As a scientist, he only improved with age. One must record here his last “heat” with heavy-element chemistry, when he introduced relativistic terms in the MOLCAS package, single-handedly developed basis sets, and ran a number of classical applications. Perhaps, the crowning achievement was the understanding of the chemical bond in U2, published in Nature in 2005. His last papers are still appearing posthumously. Björn's scientific competence and intellectual discipline had as their vehicle an outspoken personality. This made his surrounding a magic circle that was free of any pretensions or ambiguities. We miss his sardonic laughter. Björn's last decade was shadowed by cancer. He is missed by his wife Ingela, and by five children from two marriages.