Introduction

Abstract

The planning of this issue started as a project to honor Per-Olov Löwdin and his contributions to scientific research and education. His unexpected death on October 6, 2000, means that this issue honors rather the memory of Per-Olov and his work. This project was enthusiastically embraced by many friends and colleagues of Per-Olov around the world and the number of articles grew well beyond what was originally planned, a situation that put strains on the pool of referees of the International Journal of Quantum Chemistry. Although this large number of contributed articles from around the world represents a fitting tribute to Per-Olov's memory, it has resulted in the publication of this issue taking longer than originally planned. Per-Olov Löwdin earned his D.Sc. at Uppsala University. His professor, Ivar Waller, held the chair of Theoretical Physics at Uppsala. Per-Olov's dissertation, presented and defended in 1948, involved a quantum mechanical treatment of the cohesive properties of alkali halides. The impressive numerical work, carried out before the age of electronic computers, was performed on electrically powered hand calculators with the aid of a number of physics and mathematics students, many of whom went on to enjoy illustrious academic careers. This monumental project, which must have required exceptional organizational skill, the acquisition of financial resources, the gift of persuasion, and sheer enthusiasm, was typical of the many projects and ventures that Per-Olov initiated during his career. After teaching in his home department of Theoretical Physics at Uppsala (1948–1955) Per-Olov held a position with the Swedish Natural Research Council until 1960. During this time he established the Uppsala Quantum Chemistry Group. Financed by several Swedish and U.S. research grants this group consisted of several students, postdocs, and senior scientists from Sweden, the United States, Great Britain, Israel, India, Japan, Latin America, and other nations. In 1960 Per-Olov almost simultaneously accepted the positions of Professor of Quantum Chemistry at Uppsala University and of Graduate Research Professor of Chemistry and Physics at the University of Florida. From then on Per-Olov and his family had their base of operations for half the year in Sweden and half the year in Florida. Per-Olov was the Founding Editor of this journal and of Advances in Quantum Chemistry. He initiated the annual Sanibel Symposia and the Scandinavian Summer Schools in Quantum Chemistry and Solid State Theory. The Summer Schools were organized with his junior colleagues from 1958 to 1987. These schools lasted for up to six weeks, had solid financial support, and over these years taught a total of over 4000 students about linear algebra, group theory, Hartree–Fock theory, numerical methods, perturbation theory, electron correlation, etc. Students brought back heavy notebooks to their home institutions. In addition to virtually all European countries, participants came from many African, American, and Asian nations. The first Sanibel Symposium was arranged in December/January of 1960–1961. These meetings became equally international in scope. The most recent Sanibel Symposium held in February 2002 was number 42. Per-Olov participated in every one of these meetings held during his lifetime; his last one was Sanibel 2000. Having been his student and postdoc, co-organizers, and colleagues we may have a unique perspective of Per-Olov as a scientist and as a human being. He was an inspiring teacher, a gifted scientist with a mathematical bent, and an untiring lecturer. He was also determined, sometimes unyielding, convincing, charming, never boring, and always fun to be around. His most outstanding personal and professional trait may be that of an internationalist. The broad international participation of the Summer and Winter Schools and the Sanibel Symposia with typically in excess of 30 nations represented have clearly helped to promote understanding and mutual appreciation among scientists, young and old, from various cultures and national origins.