The Nobel history of computational chemistry. A personal perspective

Abstract

This article presents a personal view of selected Nobel Prizes in Chemistry. It is neither a comprehensive account of the science for which the Prizes were awarded, nor does it offer complete biographies of a remarkable group of scientists. It attempts to show the links between the prizes and chronicles the author's contacts with leading scientists over a span of almost six decades. I have used the official website of the Nobel Prizes¹ as my primary source of information and Wikipedia² as the secondary source. In a few cases, I have obtained information from reliable sources such as the Biographical Memoirs of the Fellows of the Royal Society.³ I cannot provide references for my personal reminiscences.

Some momentous discoveries and innovations can be connected to a particular moment in the history of humankind, whereas the emergence of other fields of human endeavor cannot be placed in time, nor associated with one individual or society. Computational chemistry is a prime example of the latter. It did not begin with one eureka moment, nor with a group of researchers, but rather evolved over several decades due to a myriad of factors, the two principal ones being scientific advances and technological innovations.

Experimental chemistry is primarily associated with the synthesis of molecules and materials or with reproducible measurements of observable properties, including the identification and quantification of chemical species. The fundamental basis of experimental chemistry was established in the 18th century by Antoine-Laurent de Lavoisier who was the first known person to record careful quantitative observations. The subsequent application of the scientific method over the next 250 years led to a remarkable list of achievements and established chemistry as a mature discipline. Given its relationship with the other natural sciences, chemistry is justifiably referred to as the central science.

Many chemical reactions have been known since antiquity; combustion and fermentation are classic examples. The earliest attempts to explain chemical phenomena lacked scientific rigor. A well-known example attributed to ancient Greek philosophers was the supposition that all substances are composed of four basic elements (fire, water, air, and earth). Attempts by philosophers in many societies to explain natural phenomena in terms of Empedocles' four-element theory eventually gave way to the atomic theory, introduced by John Dalton in 1808 and firmly established by the experiments of Ernest Rutherford in 1911.

The primary objective of theoretical and computational chemistry is to explain chemical phenomena involving atoms, molecules, and materials and to make predictions about the properties and transformations of matter. Theoretical and computational chemistry are inextricably linked, with the former providing a rigorous theoretical framework, while the latter uses computers to apply the methods of theoretical chemistry to a broad range of topics in chemistry. A historical account of the development of computational chemistry must by necessity include a summary of the major milestones in the history of theoretical chemistry. As noted previously, computational chemistry was a natural outgrowth of theoretical chemistry because of the rapid development of computers. Initially, the capabilities of computational chemistry were very modest, but by the end of the 20th century computational chemistry was established as one of the principal areas of chemistry. The evolution of computational chemistry resulted from a combination of advances in theoretical methods, the development of powerful algorithms and software, and innovations in computer technology.

A history of the development of computational chemistry could be written from many perspectives. For example, it could trace the history of electronic structure calculations on atoms, molecules, and materials from about 1925 with the advent of quantum mechanics to the present. Such an account would require a detailed description of many different approaches and would be a monumental task that could easily amount to several volumes. Unfortunately, such a historical record would be incomplete because it would not include thermodynamics and statistical mechanics. To cite one example, enzymatic reactions cannot be explained by electronic structure calculations alone. The approach taken in this article is to chronicle the history of computational chemistry from the perspective of the Nobel Prizes that celebrate advances in theoretical and computational chemistry or achievements that contain a significant theoretical component. Based on these criteria, the author has identified fourteen Nobel Prizes in Chemistry that are relevant to the development of computational chemistry (see Table 1). Section 16 discusses the Nobel Prizes in Physics which have a connection with computational and theoretical chemistry.

The first Nobel Prize in Chemistry was awarded in 1901 to Jacobus Henricus van't Hoff “in recognition of the extraordinary services he has rendered by the discovery of the laws of chemical dynamics and osmotic pressure in solutions”. Van't Hoff formulated the osmotic pressure law and explained how concentrations equalize between solutions that are separated by a membrane that allows the solvent to pass through but not the solute. He conducted some of the earliest studies on the rates of chemical reactions and how temperature affects them. Van't Hoff also made pioneering contributions to our understanding of the structures of molecules, including stereochemistry. He described the concept of the asymmetrical carbon atom, and he pointed out the relationship between optical activity and the presence of an asymmetrical carbon atom. Here it should be noted that Louis Pasteur discovered molecular chirality in 1848, a half century before the introduction of the Nobel Prizes. In view of van't Hoff's theoretical investigations and his insight into kinetics, thermodynamics, and other topics in chemistry, he has been referred to as a leading theoretical chemist of his time. He is also considered to be one of the founders of physical chemistry. With Wilhelm Ostwald, he established Zeitschrift für physikalische Chemie in 1887.

Van't Hoff was born in 1852 in Rotterdam, Netherlands and died in 1911 in Steglitz, near Berlin, Germany. He was a professor at the University of Amsterdam for 18 years, before moving in 1896 to the University of Berlin for the last 15 years of his remarkable career. A lighter teaching load in Berlin afforded him more time for research. His earliest research was focused on organic chemistry, but his interests shifted to many fundamental topics in physical chemistry, which led to the seminal contributions that were recognized by the first Nobel Prize in Chemistry and many other major awards.

The third Nobel Prize in chemistry, and the second one to recognize an advance in theoretical chemistry, was awarded 1903 to Svante August Arrhenius “in recognition of the extraordinary services he has rendered to the advancement of chemistry by his electrolytic theory of dissociation”. In the 19th century, it became apparent that there is a connection between chemical and electrical phenomena, but the precise details of the relationship were unknown. Svante Arrhenius studied how electrical current is conducted in chemical solutions and in 1883 he proposed a theory that when sodium chloride is dissolved in water, it splits into sodium ions with positive electrical charges and chlorine ions with negative charges. These electrically charged atoms, named ions by Michael Faraday many years earlier, allow the solution to conduct electricity.

Arrhenius was born in 1859 near Uppsala, Sweden and died in Stockholm, Sweden in 1927. His doctoral thesis on electrical conductivity contained many of the contributions for which he later received numerous awards, including the Nobel Prize. His thesis did not impress his professors at Uppsala University and so Arrhenius sent it to several leading physical chemists abroad, including van't Hoff, who were quick to appreciate the importance of his discoveries. Wilhelm Ostwald tried to persuade him to move to Germany, but Arrhenius accepted an appointment at Uppsala and later moved to Stockholm University. It is interesting to note that van't Hoff worked on Arrhenius's theory of the dissociation of electrolytes and provided physical justification for the Arrhenius equation in 1889, the same year in which Arrhenius introduced the concept of the activation energy, a barrier that must be overcome before molecules will react. The well-known Arrhenius equation describes the rate at which a reaction proceeds in terms of the activation energy and temperature.

The 1936 Nobel Prize in Chemistry was awarded to Petrus (Peter) Josephus Wilhelmus Debye “for his contributions to our knowledge of molecular structure through his investigations on dipole moments and on the diffraction of X-rays and electrons in gases”. Debye made his first major contribution in 1912 when he introduced the concept of the dipole moment of asymmetrical molecules. Symmetrical molecules such as O₂, CH₄, SF₆, and benzene, C₆H₆, have uniform charge distributions and are said to be nonpolar, whereas polar molecules such as HF, H₂O, NH₃, and CHCl₃ have nonuniform charge distributions which give rise to permanent dipole moments, which are measured in debyes. Debye worked on many topics, including the Debye-Hückel theory which was an improvement of Arrhenius' theory of electrolyte conductance in electrolytic solutions.

Peter Debye was born in 1884 in Maastricht, Netherlands and died in Ithaca, New York in 1966. He studied under Arnold Sommerfeld in Aachen and followed Sommerfeld to Munich, where he received his PhD in 1908 for a dissertation on radiation pressure. When Albert Einstein left the University of Zurich in 1911, Debye succeeded him as Professor of Theoretical Physics. Debye subsequently held positions in Utrecht and Göttingen before returning to Zurich as Professor of Physics and Principal of ETH Zurich. After holding positions in Leipzig and Berlin, he moved in 1940 to Cornell University, where during the previous year he had presented the Baker Lectures in Chemistry. He was very instrumental in building the reputation of Cornell University in chemistry and physics and remained there for the rest of his career.

In 1954, Linus Pauling received the Nobel Prize in Chemistry “for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances”. The prize was not awarded for a single discovery, but rather recognized Pauling's many contributions to the theory of the chemical bond and the structures of biological molecules. He is acknowledged to be a founder of quantum chemistry and molecular biology, two seemingly unrelated fields in the 1950s.

Pauling was born in Portland, Oregon in 1901 and died in Big Sur, California in 1994. Upon completing his PhD at the California Institute of Technology in 1925, he received a two-year Guggenheim Fellowship which enabled him to spend his formative years with Arnold Sommerfeld, Niels Bohr, and Erwin Schrödinger, three pioneers in the rapidly developing field of quantum mechanics. After a very fruitful sojourn in Europe, he returned to Caltech as an assistant professor and remained there until his formal retirement in 1958.

He received the Nobel Peace Prize in 1962 “for his fight against the nuclear arms race between East and West”. He is the only person to have won two unshared Nobel Prizes. Furthermore, he has the distinction of being one of only two people to date to win the Nobel Prize in two different fields, the other being Marie Curie who won the 1903 Nobel Prize in Physics and 1911 Nobel Prize in Chemistry.

Two approaches to electronic structure calculations emerged in the early days of applying quantum mechanics to chemistry. The two methods are known as valence bond (VB) theory and molecular orbital (MO) theory. The 1954 Nobel Prize in Chemistry recognized that Linus Pauling pioneered the valence bond method, which is based on the concept of the electron-pair bond proposed by G.N. Lewis. John C. Slater also played a major role in developing VB theory. The MO approach was proposed in 1927 by Robert S. Mulliken and Friedrich Hund when they proposed a method to interpret the spectra of diatomic molecules by assigning electrons to molecular orbitals that extend over the molecule. Robert S. Mulliken was awarded the 1966 Nobel Prize in Chemistry “for his fundamental work concerning chemical bonds and the electronic structure of molecules by the molecular orbital method”. The first accurate MO calculation was carried out in 1938 on the hydrogen molecule by Charles A. Coulson.⁴ Many other pioneers contributed to the development of the MO and VB methods.

Mulliken was born in Newburyport, Massachusetts in 1896 and died in Arlington, Virginia in 1986. He received his PhD from the University of Chicago in 1921 and like Pauling he spent two years as a postdoctoral fellow in Europe with many of the pioneers of quantum mechanics, several of whom won the Nobel Prize. During his formative years, Mulliken worked with Max Born, Louis de Broglie, Paul Dirac, Werner Heisenberg, and Erwin Schrödinger, among others. After two years at New York University, he returned to the University of Chicago in 1928 and remained there for the duration of his distinguished career.

Although Robert Mulliken and Linus Pauling shared some common interests, they were very different personalities. Mulliken was educated as a physicist and had a very focused research career that culminated with a Nobel Prize at the age of 70. Pauling on the other hand was not only a chemist; he was also a biochemist, chemical engineer, and peace activist. The author of this article had the good fortune to hear Linus Pauling speak twice in the same day in September 1967. It was my first month as an undergraduate at the University of British Columbia. Pauling gave a tour-de-force lecture on the structure of proteins to an overflow audience during the day and an impassioned plea for peace to an audience of thousands in the evening. Although much of his research lecture was beyond me at the time, I recall his animated and engaging style, which inspired me to pursue my studies in chemistry and eventually an academic career. A few years later as a graduate student, I heard Mulliken speak. His style was much more restrained and deliberate than that of Pauling. It appears that Mulliken, unlike many Nobel Laureates, had few interests beyond developing our understanding of molecular structures and spectra.

The 1968 Nobel Prize in Chemistry was awarded to Lars Onsager “for the discovery of the reciprocal relations bearing his name, which are fundamental for the thermodynamics of irreversible processes”. He provided the first complete description of irreversible relaxation of dissipative processes by analyzing their relationship with fluctuations in equilibrium states. He discovered the Onsager reciprocal relations in 1929 and published them in an expanded form in 1931. A few years earlier he refined the famous Debye-Hückel theory by allowing for the conductance of strong electrolytes.

Onsager was born in 1903 in Oslo, Norway and died in Coral Gables, Florida in 1976. Unlike most of the other Nobel Prize winners discussed in this article, Onsager's early career progressed slowly. Although he was brilliant at developing theories in physical chemistry as a young man, he lacked a similar talent for teaching and as a result his appointments at Johns Hopkins and Brown Universities were not renewed. He became an assistant professor at Yale University in 1934, one year before receiving his PhD from Yale in theoretical chemistry. He was very appropriately the Josiah Willard Gibbs Professor of Theoretical Chemistry at Yale from 1945 to his formal retirement in 1972.

Gerhard Herzberg received the 1971 Nobel Prize in Chemistry “for his contributions to the knowledge of electronic structure and geometry of molecules, particularly free radicals”. During the presentation of the Nobel Prize to Herzberg, Prof. Stig Claesson of the Royal Academy of Sciences stated that “Dr. Gerhard Herzberg is generally considered to be the world's foremost molecular spectroscopist and his large institute in Ottawa is the undisputed center for such research. It is quite exceptional, in the field of science, that a single individual, however distinguished, in this way can be the leader of a whole area of research of general importance. A noted English chemist has also said that the only institutions that have previously played such a role were the Cavendish Laboratory in Cambridge and Bohr's institute in Copenhagen”. Although he was primarily known for his seminal work in spectroscopy, he published several purely theoretical papers. In this context, I would like to mention that I used his wavefunctions⁵ for the first two excited states of helium during my postdoctoral research⁶ with Charles Coulson.

Herzberg was born in 1904 in Hamburg, Germany and died in 1999 in Ottawa, Canada. He was educated in Hamburg and Darmstadt and carried out postdoctoral research with James Franck and Max Born at the University of Göttingen. Herzberg and his wife and fellow researcher, Luise Herzberg, left Germany in 1935 when the Nazi Party introduced a law that banned men with Jewish wives from working in universities. After ten years at the University of Saskatchewan and three at the University of Chicago, he joined the National Research Council of Canada in 1948 and remained there for the remainder of his remarkable career. He wrote many highly influential books, including the four-volume series, Molecular Spectra and Molecular Structure, which were essential reference books for all spectroscopists and many theoretical chemists.

As a very naïve graduate student, I wrote to Herzberg shortly after begining my PhD research at McGill University in 1967 to inquire if he had any recent values for the equilibrium bond lengths and bond dissociation energies of diatomic molecules. To my amazement he replied within one week and explained why there was considerable uncertainty about some of the values in his 1960 book on diatomic molecules. In 1983 I had the pleasure of hosting Herzberg at a theoretical conference. I fondly recall a foggy evening on a 72-foot ketch in Halifax harbor with Gerhard Herzberg reminiscing about famous theoreticians. He was at the time Canada's most famous living scientist.

The 1974 Nobel Prize in Chemistry was awarded to Paul J. Flory “for his fundamental achievements, both theoretical and experimental, in the physical chemistry of the macromolecules”. He spent his entire career focused on the fundamental properties of macromolecules and is associated with many achievements including the Flory convention, which is a mathematical procedure to label the rotational isomers of polymers. He introduced the concept of excluded volume and developed a method to treat the effect of the excluded volume on the configuration of polymer chains. He also introduced the concept of the theta point, which is related to the excluded volume.

Flory was born in 1910 in Sterling, Illinois and died in 1985 in Big Sur, California, as did Pauling about 9 years later. He received his formal education in the American Midwest, including his PhD from Ohio State University in 1934. Unlike Pauling, Mulliken, and Onsager, Flory did not gain postdoctoral experience in Europe. He was also the first Nobel Laureate included in this article to spend a significant portion of his career in industry. His transition to academia was facilitated by an invitation from Peter Debye to hold a distinguished lectureship at Cornell University. He became a professor at Cornell University in 1948, 14 years after receiving his PhD. He moved to Stanford University in 1966 and remained there for the rest of his career.

William (Bill) N. Lipscomb received the 1976 Nobel Prize in Chemistry “for his studies on the structures of boranes illuminating problems of chemical bonding”. Boranes, compounds of boron and hydrogen, bear no relation to hydrocarbons and exhibit totally different structures due to fundamental differences in their bonding. Ethane, C₂H₆, contains a C-C single bond, whereas in diborane, B₂H₆, the two boron atoms are connected via bridging hydrogen atoms. Lipscomb used X-ray crystallography and molecular orbital calculations to elucidate the structures of boranes and to explain their highly reactive behavior when exposed to other compounds. The electron-deficient nature of boron compounds has been frequently used to produce new chemical entities with desired structures and properties. In a sense, Lipscomb's Nobel Prize can be regarded as a continuation of the elucidation of the nature of the chemical bond by his doctoral advisor, Linus Pauling. Much of Lipscomb's later work led to seminal contributions on the structure and function of large biological molecules.

Lipscomb was born in 1919 in Cleveland, Ohio and died in 2011 in Cambridge, Massachusetts. He received his early education in Kentucky and entered the University of Kentucky on a music scholarship. While in Lexington, he followed up on his childhood interest in chemistry and graduated in 1941 with a degree in chemistry. He started graduate school in physics at Caltech, having shown an interest in special relativity as a high school student, but under the influence of Linus Pauling he switched to chemistry in 1942. He joined the faculty of the University of Minnesota in 1946 and moved to Harvard University in 1959, where he remained until his retirement in 1990. His other passions in life were tennis and performing chamber music as a clarinetist.

I had the pleasure of meeting Bill Lipscomb in 1982 when he came to Dalhousie University to give the Walter J. Chute Lectures. He was the third eminent chemist to give the lectures in honor of the sixth and last Head of the Department of Chemistry. I was still building my research group at the time and although I was intimidated by the opportunity of a one-on-one discussion with a polymath, he soon put me at ease and encouraged me to follow my passions.

The 1977 Nobel Prize in Chemistry was awarded to Ilya Prigogine “for his contributions to non-equilibrium thermodynamics, particularly the theory of dissipative structures”. It was the second Nobel Prize in Chemistry for major advances in thermodynamics, the branch of science whose laws govern the physical and chemical processes of large systems in Nature. Whereas Onsager's approach was based on assumptions that a system is close to equilibrium, Prigogine successfully extended thermodynamics to treat systems that are far from thermodynamic equilibrium. He introduced the idea of dissipative structures, which can only exist in symbiosis with their surroundings whereas equilibrium structures, such as table salt and crystalline materials, can exist as isolated structures. The discovery of dissipative structures led to discoveries and applications beyond chemistry, including the description of phenomena in social systems.

Prigogine was born in 1917 in Moscow, Russia a few months before the revolution and died in 2003 in Brussels, Belgium. Unhappy with the new Russian regime, his family lived in Germany for a few years as migrants before settling in Brussels where Prigogine attended school and university. He studied chemistry and physics at the Free University of Brussels and received the equivalent of a master's degree in both in 1939 and his PhD in chemistry in 1941. His distinguished career was mainly spent in Belgium, primarily at his alma mater, and in the United States, at the University of Texas at Austin and the Enrico Fermi Institute at the University of Chicago (1961–1966). According to his mother, he was able to read musical scores before he could read printed words and so it is not surprising that he began playing the piano at a young age. Playing the piano remained his favorite lifelong pastime. He joined the Belgian nobility in 1959 when he was awarded the title Viscount by the King.

It is interesting to note that Prigogine's name has not been immortalized to the same extent as those of many scientists who laid the foundations of thermodynamics. For example, the names of Boltzmann, Carnot, Clausius, Gibbs, Joule, Lord Kelvin, Nernst, and Watt are attached to well-known units, laws, and processes.

The eight Nobel Prizes described above were awarded to individuals, as were all the other Nobel Prizes in Chemistry prior to 1929. The terms of Alfred Nobel's will allow for the Prizes to be shared by a maximum of three individuals. In fact, most of the Prizes in the past few decades have been shared by two or three scientists. Kenichi Fukui and Roald Hoffmann received the 1981 Nobel Prize in Chemistry “for their theories, developed independently, concerning the course of chemical reactions”. Whereas Pauling, Mulliken, and Lipscomb were recognized for their fundamental work relating to the structures of molecules, Fukui and Hoffmann built upon advances in quantum mechanics and experimental observations to propose theories for the chemical reactivity of molecules, such as pericyclic reactions in organic chemistry. Fukui's frontier orbital theory did not receive much attention initially, but after Hoffmann built upon his earlier work with R.B. Woodward (1965 Nobel Prize in Chemistry) their independent discoveries were combined into the theory of the conservation of orbital symmetry, which explains the products, including the stereochemistry, of many chemical reactions. By considering the symmetry properties of orbitals, Fukui and Hoffmann explained why some reactions proceed under thermal conditions, whereas others do not proceed because they are forbidden by orbital symmetry. Furthermore, they were able explain why some thermally forbidden reactions proceed rapidly under photochemical conditions.

Fukui was born in 1918 in Nara, Japan and died in 1998 in Kyoto, Japan. He was the first person of East Asian ancestry to win the Nobel Prize in Chemistry.⁷ As an undergraduate student he was very interested in quantum mechanics, especially the Schrödinger equation. His graduate research was carried out in the Department of Fuel Chemistry in the Faculty of Engineering at Kyoto University. He worked on basic aspects of engineering in the high-pressure synthesis of polyethylene which led to his 1948 doctoral thesis on the theoretical study of temperature distributions in the reactors of chemical industry. Three copies of his thesis were required, all handwritten in those days. His wife, Tomoe, helped him produce the copies and as a result her handwriting was mixed with his. He was a professor at Kyoto University from 1951 to 1982. He was primarily an experimental chemist in the early years at Kyoto, but he built up a subgroup of theoreticians in his research group. He earned his place in the annals of chemistry in 1952 when he discovered a correlation between the frontier electron density and the chemical reactivity of aromatic hydrocarbons. By 1972 he had published about 200 papers on the theory of chemical reactions for which he received many honors, including the Nobel Prize in 1981. For most of his career the frontier orbital approach provided the basis of many theoretical and experimental projects in his research group. Even Nobel Prize winners in the national universities of Japan were subject to mandatory retirement and so he became the President of the Kyoto Institute of Technology from 1982 to 1988. Before their marriage, he took Tomoe to a concert after which he noted that they had not played some parts of the symphony as written on the score. Fukui was not only a remarkable scientist, but he had a tremendous ear for music.

Early in my career I heard Fukui speak at an International Congress of Quantum Chemistry, but I never had an opportunity to meet him. He had retired from Kyoto University by the time I visited in 1986 on a lecture tour organized by his former and highly successful student Keiji Morokuma. At the time, I was disappointed that I was not able to discuss my research interests with the dean of the Japanese school of theoretical chemistry.

Roald Hoffmann was born in 1937 in Zloczow, Poland (now Ukraine) and survived many difficult years in the ghetto and a labour camp. Roald's father smuggled Roald and his mother out of the camp in 1943 and arranged for them to be hidden in the attic of a schoolhouse for the remainder of the war. Roald's father was killed in 1943 by the Nazis. His mother remarried in 1949 and the family moved to the United States where Roald graduated from high school, while learning his sixth language, English. He enrolled at Columbia College as a premedical student, but he discovered the joys of research during summer placements at the National Bureau of Standards and the Brookhaven National Laboratory and chose to study chemistry. He started graduate work at Harvard in 1958 and received his PhD in 1962, as the first Harvard PhD of both Martin Gouterman and Bill Lipscomb. During his time as a graduate student, he attended P.O. Löwdin's Summer School in Uppsala and spent nine months as an exchange student at Moscow University with A.S. Davydov, while becoming proficient in Russian. He held a Junior Fellowship in the Society of Fellows at Harvard University from 1962 to 1965. In the Spring of 1964, R.B. Woodward asked him some questions about electrocyclic reactions, which led to an amazingly fruitful collaboration and the publication of the Woodward-Hoffmann rules in 1965. Hoffmann joined the faculty of Cornell University in 1965 and has remained there, most recently as the Frank H.T. Rhodes Professor Emeritus.

I met Roald Hoffmann in 1983 in Halifax when he agreed to be a plenary speaker at the 8th Canadian Symposium on Theoretical Chemistry. The conference was co-organized with André Bandrauk (University of Sherbrooke). Thanks to generous funding from the Natural Sciences and Engineering Research Council of Canada, we were able to attract a stellar group of speakers with Gerhard Herzberg and Roald Hoffmann as our two marquee names. Hoffmann's inspiring lecture was one of many elegant lectures I have heard him give over the years in Canada, the United States, and other countries, including Cuba in 1996. Two of the occasions were particularly memorable. In conjunction with the 14th Canadian Symposium on Theoretical Chemistry in 2001 in Ottawa, the organizer Jim Wright (Carleton University) arranged to have the play Oxygen by Carl Djerassi and Roald Hoffmann performed at the National Arts Centre. I had the good fortune to be seated directly behind Hoffmann who was very interested to get our reaction to the play which is about the discovery of oxygen. In his Nobel Prize biography, Hoffmann noted that he almost switched to art history at Columbia, and so it is not surprising that he would write a play based on a historical event in science. My most recent encounter with the contemporary renaissance man was in July 2022, when Hoffmann gave the final plenary lecture at the twice postponed 12th Triennial Congress of the World Association of Theoretical and Computational Chemists (WATOC 2020) in Vancouver. His spell-binding lecture, “Simulation versus understanding: A tension, and not just in our profession”, covered many topics, including the moral implications of artificial intelligence (Figure 1).

Rudolph A. Marcus was awarded the 1992 Nobel Prize in Chemistry “for his contributions to the theory of electron transfer reactions in chemical systems”. Many chemical reactions involve the transfer of one or more electrons from one molecule or atom to another. Examples include the reactions in batteries, corrosion of metals, photosynthesis, the digestion of food, respiratory processes and many more. It is not an exaggeration to say that electron transfer reactions are among the most basic chemical reactions and that they are the basis of life. Marcus built upon earlier work by Arrhenius and Henry Eyring by considering changes in the structures of the reacting molecules and the solvent molecules. He showed that the speed of an electron transfer reaction in solution can be calculated from the changes in the Gibbs energy of the molecular system. A key aspect of Marcus theory is the rearrangement of charges and its influence on the solvent. Polarization of the solvent determines the Gibbs energy of activation and hence the reaction rate.

Marcus was born in 1923 in Montreal, Canada and was wheeled through the McGill University campus as a baby by his mother, who years later recounted that she had told him that he would study there someday. Upon completion of his BSc degree, he pursed graduate work on the kinetics of nitration under the supervision of Carl C. Winkler. He received his PhD from McGill in 1946 and joined the new postdoctoral fellowship program at the National Research Council of Canada in Ottawa, where he continued to study chemical reaction rates experimentally. During this time, he started to develop an interest in theoretical chemistry and decided that he would do a second postdoctoral fellowship. There were no theoretical chemists in Canada at the time and so he wrote to six prominent theoretical chemists in the United States. Oscar K. Rice at the University of North Carolina offered him a position despite his lack of experience in theoretical chemistry. His transition to being a theoretical chemist was spectacular. Within a few months, he formulated a particular case of what would later become known as RRKM (Rice-Ramsperger-Kassel-Marcus) theory. Despite his excellent credentials, he had difficulty obtaining a faculty position in 1951. After spending many years at the Polytechnic Institute of Brooklyn and the University of Illinois, he moved to California Institute of Technology in 1978 and has remained there for the rest of his remarkable career. He celebrated his 100th birthday in July 2023 by speaking at a symposium in his honor at Caltech.

The 1998 Nobel Prize in Chemistry was awarded jointly to Walter Kohn and John A. Pople. Kohn was cited “for his development of density-functional theory” and Pople “for his development of computational methods in quantum chemistry”. The press release noted that “the Laureates have each made pioneering contributions in developing methods that can be used for theoretical studies of the properties of molecules and the chemical processes in which they are involved”. In the 1960s, Kohn and Pople independently began to use digital computers to apply quantum mechanics to chemical problems, which is the objective of quantum chemistry. Prior to Kohn's seminal work, it was generally agreed that the application of quantum mechanics to the structures and properties of molecules requires a precise quantum description of individual electrons. Kohn showed that it was sufficient to know the average number of electrons located at any given point in space, which is the basis of density-functional theory.

With access to the excellent computing facilities at Carnegie Mellon University, in 1964 John Pople began to focus on developing model chemistries, a topic he had contemplated abstractly many years earlier. The Pople group made many innovations to speed up the complex computations and pioneered the development of composite methods in quantum chemistry. Their advances were incorporated in a software package called Gaussian, which used Gaussian-type orbitals in the basis sets. The first version, known as Gaussian 70, rapidly became popular in many countries. Pople stopped working on Gaussian in 1991 because of an acrimonious difference of opinion among the authors. There have been many subsequent releases of the world's most popular package for electronic structure calculations on molecules. Density-functional theory was incorporated for the first time in a separate release known as Gaussian 92/DFT.

Walter Kohn was born in 1923 in Vienna, Austria and died in 2016 in Santa Barbara, California. When he received the Nobel Prize at the age of 75, he noted that his feelings toward his native Austria remained very painful. He lived for 1.5 years as a Jewish boy under the Nazi regime, which murdered his parents and other relatives. He was sent to England under the Kindertransport rescue operation and transferred to Canada in 1940, spending time in a detention camp in Sherbrooke, Quebec. The camp provided some educational facilities which allowed him to continue his education and subsequently enter the University of Toronto. As a German national, he was not allowed to enter the chemistry building and so he opted to study physics and mathematics. After receiving his bachelor's and MA degrees in applied mathematics, he received his PhD in physics from Harvard University, where he worked on the three-body scattering problem under Julian Schwinger and came under the influence of J.H. Van Vleck. He held faculty positions at Carnegie Melon University and the University of California, San Diego, before becoming founding director of the new Institute for Theoretical Physics in 1984 at the University of California, Santa Barbara. He remained there for the rest of his life.

John Pople was born in 1925 in the Somerset seaside resort Burham-on-Sea, United Kingdom and died in 2004 in Chicago, Illinois. His father owned the principal men's clothing store in town and successfully survived the depression years. His mother came from a farming background and as a young woman tutored the children of a wealthy family. Due to the English class system, he was not allowed to attend the preparatory school in Burnham. In 1936 he enrolled in the Bristol Grammar School, which involved a long commute, two miles by bicycle, twenty-five by train, and the final mile by foot. Bristol was subject to many air attacks during World War II and so many of his classes were held in damp bomb shelters. At the age of twelve, he worked out that there were 11! possible batting orders of the eleven players on a cricket team. Later he was disappointed to learn that n! is a textbook formula for the number of permutations of n objects. He became the first member of his family to attend university when he entered Trinity College, Cambridge. He received his PhD in mathematics in 1951 under the supervision of John Lennard-Jones for a thesis titled simply “Water”. He moved to the National Physical Laboratory near London in 1958. His relocation to Carnegie Mellon University in Pittsburgh in 1964 was front page news in the UK with one London daily referring to his move with the headline “Another Brain down the Drain”. He moved to Northwestern University in 1993, where he was the Trustees Professor of Chemistry until his death.

I had the good fortune to meet Walter Kohn in June 2002 at the Steacie Institute for Molecular Sciences in Ottawa, Ontario. Dennis Salahub, then Director of the Institute, decided the National Research Council of Canada (NRC) should organize a symposium in honor of Walter Kohn who held an NRC Postdoctoral Fellowship in Copenhagen before joining the faculty of Carnegie Mellon University. Kohn told a wonderful story about a photographer taking a picture of a fountain on the UC Santa Barbara campus. He noticed that the photographer appeared to be very well equipped, and that the camera was facing in the direction of the sun. After debating with himself about whether he should offer some advice, he finally summoned the courage to suggest to the photographer that it might be better to take the picture from the other side so that the sun would be behind the camera rather than shining directly into the lens. The photographer thanked him for the suggestion and Walter Kohn meandered off to his office. Months later the university commemorated a special occasion by publishing a book with a cover photograph of the same fountain. It was a stunning photograph with the sun shining through the water fountain and individual water droplets illuminated by the sun. When he saw the book, Walter Kohn realized that he had tried to offer advice to Ansel Adams, a celebrated American landscape photographer.

My talk at the special symposium in honor of Walter Kohn was entitled, “Density Functional Theory as a Powerful Tool for the Development of Biological Models”. At the end of my talk, Kohn asked a very pertinent question related to hydrogen bonding and appeared to be satisfied with my answer, although I suspected he had hoped for a better one. Later during the coffee break, he asked me if the functionals we were using provided an adequate treatment of the many weak interactions in our systems. I replied that I thought there was a need for better functionals and that we relied upon the experts to develop better functionals. He smiled gently and thanked me for being part of the symposium. He struck me as being a brilliant scientist, and a perfect gentleman with warm feelings toward Canada. Sadly, when he sought a faculty position in Canada, he was unsuccessful. Carnegie Mellon University was desperately looking for someone to teach solid-state physics. Within 48 h of making an inquiry, he received a telegram offering him the position from which he went on to enjoy a stellar career (Figure 2).

I first met John Pople in 1981 when the Chemical Institute of Canada held its annual chemistry conference in Halifax. As one of the younger faculty members at Dalhousie University, I was called upon to play several roles, including Chair of the Scientific Program Committee. I saw it as an opportunity to organize a theoretical chemistry symposium and, despite my lack of experience, I managed to garner some financial support. Programming constraints limited me to a one-day symposium, which was subsequently expanded to a second day. My first choice for the opening speaker was John Pople. I must say that I was very surprised when he accepted my invitation because I doubt that he had even heard of me. Several very prominent Canadians agreed to participate even though I could offer no financial support beyond waiving the registration fee for a select few. I was very impressed with Pople's talk and as I will explain in a later section it rekindled thoughts about the choices that I had made years earlier. The final speaker of the morning session made a huge impression on the audience. A new postdoctoral fellow was planning to join my group about a month after the conference and so I offered him a chance to give a talk. He had an impressive academic record and had recently completed a self-supervised thesis on numerical Hartree-Fock-Slater calculations on diatomic molecules. The previous year he had written to several theoretical chemists in Canadian universities to see if they would host him as an NSERC Postdoctoral Fellow (equivalent to the award that Walter Kohn held in Copenhagen in 1950–1951). He knew exactly what he wanted to work on as a PDF and was looking for an opportunity to pursue his ideas in an appropriate environment with computing facilities. I was the first to respond to his inquiry and confirmed that he could be an independent PDF in my small group. And so, in June 1981, I met both John A. Pople and Axel D. Becke whose famous papers^{8, 9} on the development and benchmarking of exchange-correlation functionals in Kohn-Sham density-functional theory were instrumental in the awarding of the 1998 Nobel Prize in Chemistry. After three years of externally funded fellowships at Dalhousie University, Becke took up a position at Queen's University in 1984 and quickly became Canada's best known and most highly cited theoretical chemist. In 2006, he returned to Dalhousie as the Killam Chair in Computational Science.

Fritz Schaefer organized a symposium in honor of John Pople in October 1989 in Athens, Georgia. The symposium was entitled Forty Years of Quantum Chemistry. In his opening comments Schaefer said that he had chosen the dates in anticipation that there would be an announcement that John Pople was the winner of the 1989 Nobel Prize in Chemistry, and he thought it would be wonderful to have many of the world's computational chemists at a conference when the announcement was made. As it turned out, the party was scheduled nine years before the event. More than 400 participants attended the symposium. I contributed a poster entitled Electron Correlation and Electron Density Distributions based on two papers that L.C. Wang and I published in 1989. Wang wrote the code to generate the densities from Møller-Plesset perturbation theory and configuration interaction calculations using Gaussian 86. After we were returning from the barbecue, I was astonished and more than a little nervous when John Pople told me that he wanted to discuss my poster with me. It turned out that he was very interested in what we had done, and he clearly grasped the technical details faster than me. We described the technical details in a paper¹⁰ in The Journal of Chemical Physics in the same year as the symposium.

The following year I had the opportunity to host John Pople in Halifax when he gave the Walter J. Chute Distinguished Lectures at Dalhousie University. The Chute Lectures are the intellectual highlight of the year in the Department of Chemistry. Many of the speakers were Nobel Laureates and many others gave the Chute Lectures before going to Stockholm. I am happy to say that John Pople was among the latter. John Pople was the second theoretical chemist to give the Chute Lectures and some of my colleagues questioned the choice. After hearing his splendid talks, I heard nothing but compliments about the choice, which was done through a very open and transparent procedure. The Poples' itinerary allowed an afternoon for sightseeing and so I took them to Peggy's Cove and a seaside restaurant for lunch. It was a very foggy day in November. Joy in her charming English accent kept saying how lovely it was to which John replied with his wry and wonderful sense of humor, “you must be seeing more than me”. John married his piano teacher, Joy Bowers, in 1952, soon after the completion of his PhD. They were married for 50 years until Joy died in 2002. It was clear to me from their 1990 visit to Halifax, that John was very dependent upon Joy and so it is perhaps not surprising that he did not live long after her passing. I don't think it is widely known that John Pople was knighted by Queen Elizabeth in 2003, the year before he passed away. I suspect that had he lived longer he would have cracked a small smile when introduced as Sir John before giving a remarkably clear lecture on his latest interest in computational chemistry.

I had several more memorable interactions with John Pople, including a conference in Cambridge that Nicholas Handy organized in September 1995 in memory of S. F. Boys and in honor of Isaiah Shavitt, two highly influential pioneers of quantum chemistry. In December the same year, Suehiro Iwata, Leo Radom, Fritz Schaefer, and I organized a symposium at the 1995 International Chemical Congress of Pacific Basin Societies in Honolulu in honor of John Pople. As I recall, almost everyone we invited to speak accepted our invitation and I think Pople attended every invited talk. On both occasions, I listened carefully to Pople's splendid talks (Figure 3).

It was a great honor for me to be invited to speak in March 2005 at the ACS Memorial Symposium in Honor of John Pople in San Diego. In my talk, entitled Computational Studies on Biomolecules and Reaction Mechanisms, I noted that our contributions to the field would have been impossible without John Pople's careful systematic studies and his development of model chemistries. Although I was not a student of John Pople, I learned more from his papers and books than I did from any other person in theoretical and computational chemistry.

The 2013 Nobel Prize in Chemistry was awarded jointly to Martin Karplus, Michael Levitt, and Arieh Warshel “for the development of multiscale methods for complex chemical systems”. For many years there was much speculation among computational chemists about when would the Royal Swedish Academy of Sciences recognize the remarkable developments in molecular dynamics simulations. The suspense ended on the 9th of October 2013 with the press release from Stockholm. Karplus, Levitt, and Warshel were recognized for combining the classical physics of Newton for treating part of a system, such as a solvent, with quantum mechanical methods for other parts of a system, such as the active site in an enzymatic reaction. It is interesting that in his Nobel Lecture, Martin Karplus noted he was disappointed that molecular dynamics simulations were not mentioned in the announcement of the 2013 Nobel Prize in Chemistry.

Martin Karplus was born in 1930 in Vienna, Austria. His family fled from the Nazi occupation of Austria to Switzerland and then to France before immigrating to the United States. He graduated from Harvard College in 1951 and then pursued graduate studies at the California Institute of Technology under the supervision of Linus Pauling. Following the completion of his PhD in 1953 he was an NSF Postdoctoral Fellow with Charles Coulson at the University of Oxford for two years. He held faculty positions at the University of Illinois at Urbana-Champaign and Columbia University before joining Harvard University in 1966. Since 1996, he has divided his time between the University of Strasbourg in France and Harvard University.

Michael Levitt was born in 1947 in Pretoria, South Africa. His family moved to England when he was 15. He attended Pretoria Boys High School from 1960 to 1962 and graduated from King's College London in 1967. He received his PhD in computational structural biology from Cambridge in 1972. He was a professor of chemical physics at the Weizmann Institute from 1980 to 1987 and has been a professor of structural biology at Stanford University from 1987 to the present. He holds South African, American, British, and Israeli citizenship, which may be a record for the Nobel Laureates listed in Table 1.

Arieh Warshel was born in 1940 in Kibbutz Sde-Nahum, British Mandate of Palestine (now Israel). He received his BSc in Chemistry from the Technion, Haifa in 1966 and his PhD from the Weizmann Institute of Science in Rehovot in 1969. After three years as a postdoctoral fellow with Martin Karplus at Harvard, he returned to the Weizmann Institute in 1972. From 1972 to 1976 he divided his time between the Weizmann Institute and the Laboratory of Molecular Biology, Cambridge, England. In 1976 he moved to the University of Southern California after being denied tenure at the Weizmann Institute. He served as a soldier with the Israel Defense Forces in the 1967 Six-Day War and the 1973 Yom Kippur War.

I have heard the 2013 Laureates speak at conferences, but apart from a few brief conversations with Warshel, I have not had an opportunity to get to know them. I was fortunate to hear Martin Karplus give a Charles A. McDowell Lecture at the University of British Columbia in 2020, mere weeks before the COVID pandemic closed the university to in-person events. At the time, I reflected on the fact that his lecture was presented in a building adjacent to the one where I heard his PhD mentor Linus Pauling speak in 1967, and on how my career in computational and theoretical chemistry had been inspired by so many outstanding scientists with exceptional communication skills.

I received several comments on the contents of Table 1. It was suggested that I could have included the 1996 Nobel Prize in Chemistry awarded jointly to Robert F. Curl Jr., Sir Harold W. Kroto and Richard E. Smalley “for their discovery of fullerenes”. Although Robert Curl was interested in theoretical chemistry and spent a sabbatical with Charles Coulson, and Harry Kroto published several papers involving electronic structure calculations, I think the 1996 Nobel Prize in Chemistry celebrated a remarkable experimental discovery and does not meet the criteria I used to make the selection of the entries. I could have included some anecdotes about my interactions with Harry Kroto from 1974 to 2007, but they would not be in the context of this article.

The current state of computational chemistry could not have been achieved without the breakthroughs recognized by the Nobel Prizes in Chemistry described in the preceding sections. Moreover, it would be impossible to carry out state-of-the-art simulations of chemical phenomena without the innumerable advances in mathematics, physics, engineering, and computer science. Alfred Nobel's will established prizes in only five fields: chemistry, literature, peace, physics, and physiology or medicine. Physics is the most relevant of the Nobel disciplines to computational chemistry and therefore it is appropriate to include a section on the Nobel Prizes in Physics.

As noted above, two of the first three Nobel Prizes in Chemistry were awarded in theoretical chemistry, whereas in the case of physics, the first nine were awarded in experimental physics. The first Nobel Prize in theoretical physics was not awarded until 1910 when van der Waals was recognized for his work on equations of state. However, the number of Nobel Prizes in theoretical physics soon overtook the number in theoretical chemistry because of what we may refer to as the quantum revolution.¹¹ In 1954, Linus Pauling received the fourth prize in theoretical chemistry for his insight into the nature of the chemical bond, the same year in which the tenth prize in theoretical physics was awarded to Max Born for his insight into the statistical interpretation of wavefunctions. The number of Nobel prizes in theoretical physics continues to outnumber those in theoretical chemistry. Table 2 lists 28 Nobel Prizes in Physics that recognize an accomplishment in theoretical physics up to and including 2013, the year in which the most recent prize in theoretical chemistry was awarded.

Many of the names in Table 2 appear regularly in publications and textbooks in computational and theoretical chemistry, especially the first ten. Indeed, the names of van der Waals, Planck, Einstein, Bohr, de Broglie, Heisenberg, Schrödinger, Dirac, Fermi, Pauli, and Born are all as recognizable as the chemists listed in Table 1. The prizes in theoretical physics in recent decades have been much less pertinent to computational and theoretical chemistry. In the interest of brevity, the Nobel Prizes in Physics will not be discussed in as much detail as the Chemistry Prizes. The choice of wording for the citations is interesting. Some citations seem to be a little understated relative to others. Whereas some scientists were recognized for their work, services, contributions, demonstrations, research, studies, etc. Werner Heisenberg was recognized for the creation of quantum mechanics. In some cases, the citations are succinct and well aligned with the achievement, but in other cases the citations are cumbersome. For example, the citation for the 2013 Nobel Prize in Physics could have been simply “for their discovery of how elementary particles acquire mass”.

In the history of the Nobel Prizes, there have been several cases where more than one member of a family has received a Nobel Prize. In the context of this article, it is interesting to note that Aage Bohr, co-winner of the 1975 Physics prize, is the son of Niels Bohr, winner of the 1922 prize. Whereas the father was focussed on the electronic structure of atoms, his son made a seminal contribution to our understanding of the structure of atomic nuclei.

Examination of Tables 1 and 2 reveals that only one of the 42 Nobel Prizes recognizes the achievements of a woman. Maria Goeppert Mayer received one quarter of the 1963 Nobel Prize in Physics for her “discoveries concerning nuclear shell structure”. She grew up in an era when girls were discouraged from studying mathematics and science. Despite her exceptional talent and potential, she did not become a professor of physics until she was forty. Following her death in 1972, the American Physical Society established an award in her memory that recognizes young female physicists at the beginning of their careers. It is a fitting tribute to a leading physicist who persevered as a volunteer for many years before receiving an appropriate professional appointment and reaching the pinnacle of her discipline.

As I completed writing about the physics prizes, I began to wonder if one of the Nobel Prizes in Physiology or Medicine had been awarded for an achievement in computational biology. The answer appears to be no, but through my investigations I learned that the International Society for Computational Biology¹² (ISCB) was established in 1997. The ISCB organizes the annual Intelligent Systems for Molecular Biology conference, and awards three prizes for scientific achievements in computational biology and bioinformatics. The ISCB is similar to WATOC, the World Association of Theoretical and Computational Chemists,¹³ which organizes a triennial world congress and awards the Dirac and Schrödinger Medals.

Nobel Prizes are not normally awarded posthumously and therefore it is interesting to speculate about distinguished scientists whose contributions were not recognized by the Royal Swedish Academy of Sciences. One of the most obvious omissions in my opinion is Gilbert N. Lewis (1875–1946). In 1916, he proposed his famous theory of chemical bonding, which continues to be the basis for teaching chemical bonding to undergraduate students. Had he received the Nobel Prize, the citation might have been “for his discovery of the covalent bond and his concept of electron pairs”. As Dean of the College of Chemistry at Berkeley, Lewis mentored and influenced many Nobel Prize winners, including Harold Urey (1934), William F. Giauque (1949), Glen T. Seaborg (1951), Willard Libby (1960), and Melvin Calvin (1961). Lewis was nominated for the Nobel Prize virtually every year between 1922 and 1944.¹⁴ William B. Jensen's excellent essay¹⁵ on the mystery of G.N. Lewis's missing Nobel Prize provides insight into the nomination and selection of the Nobel Prizes, a topic which in the interest of brevity is not explored herein.

The contributions of John C. Slater (1900–1976) to computational and theoretical chemistry are commemorated by many well-known terms including Slater determinants, Slater-type orbitals, Slater integrals, Slater's rules, Slater-Condon rules, etc. After completing his PhD in physics at Harvard, Slater was a postdoctoral fellow with Niels Bohr in Copenhagen which led to the publication of the Bohr-Kramers-Slater (BKS) theory in 1924. He introduced the determinantal form (Slater determinant) for an antisymmetric wavefunction in 1929. Later, he built up the large and influential Solid State and Molecular Theory Group at MIT. He was nominated for the Nobel Prize in both Chemistry and Physics many times. Had one of the nominations been successful, the citation might have been “for his contributions to the theory of the electronic structure of atoms, molecules, and solids”.

My third selection, among many possibilities, is Charles A. Coulson (1910–1974). He studied mathematics at Trinity College, Cambridge and went on to earn his PhD in 1936 under the supervision of Sir John Lennard-Jones, the first Professor of Theoretical Chemistry in the UK. He held academic appointments in several universities in mathematics, physics, and chemistry prior to becoming the Rouse Ball Professor of Mathematics at Oxford from 1952 to 1973. He was succeeded by Sir Roger Penrose (2020 Nobel Prize in Physics). Coulson was a prolific author on many topics, which no doubt played a role in attracting many graduate students, postdoctoral fellows, and senior visitors to his group. Several members of his group subsequently became leaders in their respective fields, and a few won Nobel Prizes in Chemistry and Physics, including Peter Higgs co-winner of the 2013 Nobel Prize in Physics. Coulson's textbook Valence was nearly as influential as Pauling's The Nature of the Chemical Bond and therefore my suggestion for the citation is “for the application of the quantum theory of valency to molecular structure, dynamics and reactivity”.

I had the good fortune of joining Coulson's group as a National Research Council of Canada Postdoctoral Fellow in January 1971. It was a very international group with a broad range of research interests in theoretical chemistry and related fields, including applied mathematics. Coulson did not apply for research funding and so all members of his group had to secure their own funding. When I wrote to inquire about the possibility of being a postdoctoral fellow, he replied that the decision would be made by the NRC of Canada. Many Canadians worked with Coulson thanks to the generosity of the NRC, including Michael Robb (later Professor of Chemistry, Imperial College) who arrived the previous year. Similarly, Americans were supported by the National Science Foundation, as Martin Karplus was about 20 years earlier. I was attracted to Coulson's group by the diversity of research interests even though based on the papers I read as a graduate student a far more logical choice would have been John Pople's group at Carnegie Melon University. Every time I heard Pople speak, I was reminded that my heart had chosen Oxford, whereas my brain had told me that I should have gone to Pittsburgh. Fortunately, it worked out well for me.

For many years, Henry F. Schaefer III, a highly cited and prolific leader in computational quantum chemistry, has organized the Robert S. Mulliken and Charles A. Coulson Lectures at the University of Georgia. Robert G. Parr gave the first Mulliken Lecture in 1988, the same year that Michael J.S. Dewar gave the inaugural Coulson Lecture. It is interesting to note that John Pople and Martin Karplus gave Coulson Lectures in 1989 and 1996, respectively, many years before they were awarded their Nobel Prizes. It was a special honor for me to present the 2011 Charles A. Coulson Lecture in Athens, Georgia.

When I shared early drafts of this article with some friends and colleagues, I received many suggestions of prominent theorists who were not Nobelists to be included in this section. An obvious omission is Josiah Willard Gibbs (1839–1903). Surely, his contributions to thermodynamics and statistical mechanics were at least as significant as those of Lars Onsager and Ilya Prigogine. Unfortunately, Gibbs died shortly after the first Nobel Prizes were awarded, but not before his accomplishments were celebrated with many awards including the Copley Medal in 1901, which at the time was the most prestigious international scientific award.

There are many cases of leading figures who, like Coulson, created centres of excellence and organized summer schools and the equivalent in theoretical chemistry. A prime example is Per-Olov Löwdin (1916–2000) who made many seminal contributions to quantum chemistry while dividing his time between Uppsala University and the University of Florida. He is remembered for many contributions including being a founder of the International Academy of Quantum Molecular Science¹⁶ and establishing the International Journal of Quantum Chemistry. I had the good fortune to attend his Winter Institute in Gainesville, Florida in December 1968. I fondly recall that his enthusiasm and energy for his favorite topics was boundless.

The names of Douglas Hartree (1897–1976) and Vladimir Fock (1898–1974) are immortalized by thousands of papers that report Hartree-Fock calculations every year. Another possibility is Michael Polanyi (1891–1976) who made many theoretical contributions. His name is associated with the Bell-Evans-Polanyi principle, the Eyring-Polanyi equation, and many other textbook topics. Michael Polanyi's son John Polanyi (University of Toronto) shared the 1986 Nobel Prize in Chemistry with Dudley R. Herschbach and Yuan T. Lee “for their contributions concerning the dynamics of chemical elementary processes.” In the end, I chose not to expand this section significantly and to retain the focus on Lewis, Slater, and Coulson.

When I started high school in September 1960 in New Westminster, British Columbia, I doubt that I had heard of the Nobel Prizes. My high school was newly built and called Lester Pearson High School in honor of the winner of the 1957 Nobel Peace Prize, Lester (Mike) Bowles Pearson (1897–1972), who later served as the fourteenth Prime Minister of Canada from 1963 to 1968. We were quite proud to be attending a school named after a diplomat who played a key role in ending the Suez Crisis.

My first nine years of schooling were in Kelowna, British Columbia, then a small town where academics were much less important than sports. Grade ten was a revelation for me. I found myself among students who were highly motivated and planning to go to university, an opportunity that no one in my family had enjoyed prior to me. My favorite courses were chemistry, mathematics, and physics, and to my amazement I was successful in high school and at the University of British Columbia (UBC). In 1975, Dalhousie University was looking to hire a physical chemist; fortunately for me they lacked the resources to support an experimental chemist and they decided to take a chance on a theoretical chemist.

My first exposure to a Nobel Laureate was hearing Linus Pauling speak at UBC, as described earlier in this article. In my fourth year as an undergraduate, I was assigned to do my research project at UBC under the supervision of Professor David C. Frost. One day the Head of the Department, Charles A. McDowell, brought a distinguished looking gentleman into the lab. I was the only person in the lab at the time. Prof. McDowell asked me to tell the visitor about my research project. I told the visitor that I was trying to modify a home-built spectrometer to study the angular dependence of photoelectron emission and that I only started my project two months earlier. The visitor smiled and commented that it sounded like a rather ambitious project for an undergraduate student and continued his tour of the Department. The visitor was Ronald G.W. Norrish, cowinner of the 1967 Nobel Prize in Chemistry.

As described above, I had the pleasure of meeting John Pople, Bill Lipscomb, Roald Hoffmann, and Gerhard Herzberg in Halifax during my time at Dalhousie University. In addition, I was fortunate to speak with many previous and future Nobel Laureates who visited our department. In approximate chronological order, they are John Polanyi (1986 Nobel Prize in Chemistry), Dorothy Hodgkin (1964 Nobel Prize in Chemistry), J. Fraser Stoddart (2016 Nobel Prize in Chemistry), Richard R. Schrock (2005 Nobel Prize in Chemistry), Harry Kroto (2006 Nobel Prize in Chemistry), and Robert F. Curl (2006 Nobel Prize in Chemistry). It was a thrill and an honor to have met so many remarkable individuals who encouraged me, by their example and kind words, to pursue my academic journey in theoretical and computational chemistry.

I have written this little history in anticipation that it may inspire others to pursue their dreams and that it may have an indirect impact on the future of computational chemistry. I shall not attempt to predict the future other than to speculate that in the not-too-distant future quantum computers will have a more dramatic impact on the field than the advances in digital computer technology had during my career.