Volume 72 Number 7S July 1998
A Supplement in Honor of Włodzimierz Kołos

   Włodzimierz Kołos was born on September 6, 1928 in Pinsk (then in Poland, now in Belarus) to the family of Paweł Kołos, a railway officer, and his wife Elżbieta Saszko. He spent his early youth, during the Second World War, in Środa Wielkopolska working in a local photo laboratory in order to help his family. After the war he quickly completed his high-school education and entered the University of Poznań to study chemistry and physics. In 1950 he received his M.Sc. in chemistry and began an academic career as an organic chemist. Very soon, however, he was attracted to theoretical physics. This interest probably began during one of the summer schools in physics organized by Leopold Infeld - one of the most prominent Polish physicists of that time, famous for his collaboration with Albert Einstein. In the fall of 1951 Kołos began his graduate studies in theoretical physics under Infeld's supervision. His research topic was the influence of hindered rotation on neutron scattering off small organic molecules, a subject certainly related to his chemistry background. He completed his thesis in only two years, the shortest time we are aware of in the recent past in Poland. This was very typical of his style: concentrate on one subject, work tirelessly, penetrate to the essence of the problem, successfully complete the research, and quickly publish results. This style of scientific work would become a part of his legend.
    His striving for a deep understanding of the electronic structure of molecules directed him to a new field of research - the theory of electron correlation. Kołos became one of the first researchers to consider the problem of electron correlation in organic molecules. His early papers on the correlation of electronic motion in the ethylene and benzene molecules, published before his first stay in the USA, contained important ideas on this subject developed later by himself and others. In 1958 he went to Robert Mulliken's laboratory at the University of Chicago - the famous Laboratory of Molecular Structure and Spectra. His stay in the United States was possible because of the political relaxation which took place in Poland after the death of Stalin. In the present volume we find a memoir by Bernard Ransil recalling this period from a scientific perspective. At this time computers were being introduced as a new research tool in physics and chemistry. This development gave Kołos a unique chance to participate in the beginning of a new era in science - one of computers and large-scale scientific computations. Upon arriving in Chicago he faced the choice of either joining Robert Mulliken in his investigations on larger molecules by approximate methods, or collaborating with Clemens Roothaan on small molecules using more exact methods. In a contribution to this volume Roothaan describes how Kołos began his research on the hydrogen molecule.
    In Chicago Kołos quickly took advantage of modern electronic computers available in United States at that time. He developed a unique computer program which solved the electronic Schroedinger equation for the hydrogen molecule to spectroscopic accuracy. The program applied a basis set of functions depending explicitly on the interelectronic distance. This basis, introduced earlier by James and Coolidge, was further improved by Kołos and Lutoslaw Wolniewicz. It is now known as the Kołos-Wolniewicz basis. In the early 1960s Kołos and Wolniewicz computed several corrections to the conventional Born-Oppenheimer energy of the hydrogen molecule, including the adiabatic, non-adiabatic, and relativistic effects. These were seminal theoretical developments never before attempted for any molecule. This work resulted in theoretically predicted spectra of accuracy comparable with the best experimental data available at that time. One result of these calculations was quite unexpected. The predicted value of the dissociation energy of the hydrogen molecule was significantly larger than the experimental value measured in Gerhard Herzberg's group. This was in clear contradiction with the variational principle applied at the adiabatic level of approximation. This contradiction disappeared a few years later when Herzberg improved his experiment and obtained a new result which agreed with the theoretical prediction of Kołos and Wolniewicz. This famous development showed that quantum mechanics can, indeed, very accurately predict the properties of molecules, and that quantum chemists can sometimes be correct when their predictions disagree with the results of spectroscopic measurements. Herzberg himself attributed great weight to the agreement between the theory and experiment achieved for the hydrogen molecule, and in his Nobel lecture devoted considerable attention to a detailed discussion of this issue.
    Kołos managed to take advantage of each new generation of computers to increase the accuracy of his theoretical predictions. Together with Wolniewicz and others he improved the theoretical value of the dissociation energy several times. These improvements usually inspired new, increasingly sophisticated determinations of the experimental value. He also devoted considerable effort to the study of various spectroscopic properties of excited states of the hydrogen molecule. Collaborating with Wolniewicz, and later with Jacek Rychlewski, he obtained numerous accurate potential energy curves which have been invaluable not only in interpreting spectroscopic experiments, but also in other, sometimes exotic, fields of science like the Bose-Einstein condensation of spin-polarized hydrogen, or collision physics involving ultra-cold hydrogen atoms. Accurate calculations for the excited states also resolved the longstanding controversy concerning the relative location of the triplet and singlet states of the hydrogen molecule. Although Kołos continued theoretical research on the hydrogen molecule until the end of his life, his scientific interests were very broad, and he was active in many other areas. He made important theoretical contributions to the theory of intermolecular forces and founded a strong research group in this field in Warsaw. By studying with great precision the interaction of two hydrogen atoms he established the validity and potential accuracy of various approximations commonly used in the theory of intermolecular forces. Along with his younger collaborators from Warsaw, he studied the foundations of the perturbation theory of intermolecular forces and contributed to the development of the current formulation of the symmetry-adapted perturbation theory. He was also one of the pioneers in the field of ab initio studies of the nonadditivity of intermolecular forces. His interest in this area ranged from the interaction of closed-shell atoms, through non-polar molecules like methane, to interacting polar systems like water molecules in the water trimer. His work, which pointed out to the importance of many-body effects, is fully appreciated only now when the studies of many-body forces became very important in the context of rapidly developing molecular cluster studies. In the 1980s Kołos was involved in theoretical studies of molecular final states in the ß-decay of molecular and solid tritium, a subject related to his work on the hydrogen molecule. This work was carried out in collaboration with the experimental group at Lawrence Livermore National Laboratory in an effort to determine the mass of the electron neutrino. Actually, the Livermore group invited him to conduct this study in recognition of the outstanding quality of his earlier work on the hydrogen molecule. Together with his collaborators from Warsaw, Gainesville, and Livermore, he computed the energies and wave functions for all final states of HeT+ ion produced in the ß-decay of the T2 molecule, and determined the transition probabilities corresponding to each of the final states. Using these transition probabilities, the theoretical spectrum of the emitted beta particles could be studied as a function of the hypothetical neutrino mass. These results have been used, and are still used, to interpret tritium-decay neutrino-mass experiments. They may help, in a sense, to predict the fate of the Universe, which will expand forever or collapse depending on the actual value of the neutrino mass.
    Kołos's involvement in the research on muon-catalyzed fusion provides another example of his interdisciplinary scientific activity. He became interested in this subject in the late 1950s and his first calculation of the fusion rate was published in a 1960 paper co-authored by Roothaan and Robert Sack. Renewed interest in this field arose in the 1980s when new experiments indicated that a single muon can catalyze hundreds of fusion reactions and that, with further improvements, the released nuclear energy may be larger than the energy needed to produce muons. Together with his collaborators from Warsaw and Gainesville, Kołos performed extremely accurate nonadiabatic calculations for the molecular ion composed of muon, deuteron, and triton. These calculations had to include not only the Coulombic, but also the strong nuclear force acting between the tritium and deuterium nuclei. The obtained results showed that, contrary to various earlier speculations, the achieved experimental fusion yield is very close to the theoretical limit, and the only way to increase the efficiency of this process is to reactivate muons captured by alpha particles.
    Kołos's achievements were quickly recognized in Poland and abroad. He received numerous medals and awards, including the Sniadecki and Copernicus Medals, the Medal of the Israel Academy of Sciences, the Alexander von Humboldt Award, the Jurzykowski Award, and the Swietoslawski Award. In 1967 he was the very first recipient of the Annual Medal of the International Academy of Quantum Molecular Sciences. Later, in 1988, he became a member of this Academy. In 1969 he was elected to the Polish Academy of Sciences and in 1994 to the Academia Europea. In 1992 he received an honorary doctorate from his Alma Mater: Adam Mickiewicz University of Poznan, and was deeply touched by this distinction and in 1994 became a Honorary Member of the Polish Chemical Society. He was a member of editorial boards of a number of scientific journals, including the International Journal of Quantum Chemistry, Chemical Physics Letters, Journal of Molecular Structure (Theochem), Theoretica Chimica Acta, and Polish Journal of Chemistry.
    His papers have been and still are widely known and cited. Until now they received almost 5000 literature citations. One of these papers - "Potential Energy Curves for the X1 SIGMAg+, b3SIGMA u+ and C1PI u States of the Hydrogen Molecule" - published with Wolniewicz in the Journal of Chemical Physics in 1965, received over 500 citations and was featured as a Citation Classic in Current Contents. Another article - "Nonadiabatic Theory for Diatomic Molecules and its Applications to the Hydrogen Molecule" - published in 1963, also with Wolniewicz, was listed as one of the one hundred most cited articles which appeared in the Reviews of Modern Physics. Also, several of his papers devoted to intermolecular interactions received a very large number of citations.
    After short periods when he worked at the Institute of Physical Chemistry of the Polish Academy of Sciences and at the Institute of Nuclear Research, in 1962 Kołos settled at the Department of Chemistry of the University of Warsaw where he had worked until his untimely death. He traveled frequently, spending sabbaticals with visiting appointments at various institutions including the Universities of Chicago, Mexico, and Florida, the Max Planck Institute in Garching, and Montedison Institute in Italy. Upon receiving the Alexander von Humboldt Award, he selected Garching as his research place.
    At the University of Warsaw Kołos devoted a large part of his time and energy to various educational and administrative activities. From 1990 until 1993 he served as the Chairman of the Chemistry Department. During his term he initiated many changes which transformed our Department into a more modern educational and research institution. He was an inspiring lecturer loved and admired by his students. His lectures on quantum chemistry were many times voted as the best courses at the Department of Chemistry - a very unusual feat for the subject usually dreaded by a majority of chemistry students. His two elementary quantum chemistry textbooks, never translated into English, but very popular in Poland, are didactic masterpieces explaining chemical applications of quantum mechanics in a language accessible to chemistry students.
    Kołos's personality as well as his scientific reputation attracted many young scientists to the Quantum Chemistry Laboratory which he headed for many years. He was a great supervisor who gave his students complete freedom in their research, did not demand immediate results, and patiently waited for progress. He understood not only all intricacies of research, but also all the complications of our lives. He was always enthusiastic about his research, working relentlessly until a satisfactory solution of the problem was found. He gave us a clear example of hard work and the true devotion to science. This example was the only method he used to shape his students.
    Kołos was a very kind and modest person. Although one of Poland's most prominent scientists, he resisted any attempts to celebrate his achievements. He was always available to his students when they wanted to discuss a problem. With a shy smile he would invite us to his office and listen patiently to our sometimes naive questions. He never compromised, however, on the quality of scientific work, and insisted that it should always be measured by the best standards.
    The weekly Thursday 4:15 pm seminars, established by him, will remain our tradition. He was attentive, friendly, and curious during these seminars. He believed, however, that one should only talk about issues which one understands well. Speakers not following this principle were quickly stopped by a series of penetrating questions. If nonsense were presented, he would respond with a witty and sometimes sarcastic comment.
    We also owe our Professor a lesson of behavior as a citizen. Initially he was not interested in politics, except perhaps for an article he wrote in the 1950s, in which he defended the Pauling resonance theory, banned during the Stalinist period as "non-scientific" and "reactionary". He confined himself to his research and protected his group from any intrusion of Communist politics. Neither he nor anybody in his group was ever a member of the Communist Party, something unusual in those times. In 1980, when Solidarity was born and realistic hopes for overthrowing the Communist rule emerged, he became politically active. He became the first democratically elected Secretary of the Mathematics, Physics and Chemistry Branch of the Polish Academy of Sciences. During the gloomy time of martial law, when the Faculty Council meetings were conducted in the presence of military officers, he dared to oppose openly the Communist rule. His forceful, precisely worded statements, made in a very quiet voice clearly heard in the complete silence of the auditorium, gave us strength and hope for a future victory. After Karol Wojtyla became Pope John Paul II, Kołos frequently participated in the summer schools on science at Castel Gandolfo near Rome. He presented talks on the latest developments in science and discussed scientific issues with the Pope. Kołos had a profound interest in the philosophical foundations of science, and of quantum mechanics in particular. His last fascination was the philosophical implications of the Bell inequalities. He was always very rejuvenated after returning from Castel Gandolfo. The onset of his illness forced him to cancel at the last moment his trip to the meeting scheduled for the summer of 1995.
    His brave fight with bone cancer lasted for over one year. During this extremely difficult time his courage and dignity remained an inspiration to his friends. His spiritual strength, rooted in his deep faith in God, radiated from him even when he was permanently confined to his hospital bed. Until his last days he remained deeply interested in recent scientific news and in the life of our Department.
    Włodzimierz Kołos passed away on 3 June 1996. He will be missed very much not only as a scientific and moral authority, but also for his wonderful personality and warmth. He was a man who made full use of his talents. His life will remain an example of hard work, friendship, courage, and faith. This volume is a testament to the memory, admiration, and deep sense of loss of those who knew him.

Bogumil Jeziorski
Lucjan Piela

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© 1998 Polish Journal of Chemistry