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Vol. 26 No. 4
July-August 2004

Role Models in Chemistry:John Pople

by Balazs Hargittai and István Hargittai

Walter Kohn (left) and John Pople in Stockholm, 2001, during the Nobel Prize Centennial celebrations.
—Photo by I. Hargittai

“We are perhaps not far removed from the time when we shall be able to submit the bulk of chemical phenomena to calculation, wrote J. L. Gay-Lussac in 1888.” Although chemistry will always remain primarily an experimental science, John A. Pople did perhaps more than anybody else to make Gay-Lussac’s prophecy true. Pople (b. 1925 in Burnham-on-Sea, Somerset, England—d. 2004 in Evanston, Illinois) revolutionized chemistry by pushing it into the computer era. He was awarded the 1998 Nobel Prize in Chemistry “for his development of computational methods in quantum chemistry.” He shared the prize with Walter Kohn (b. 1923) who received it “for his development of the density-functional theory.”

Pople’s father was a local businessman and his mother came from a farming family. However, little John was told early enough that he was expected to do more than run a small business in a small town. His road to education was not without hurdles. The local preparatory school, which was of good quality, was not open to children of retail tradesmen, so John was sent to study in Bristol. Some of his school years coincided with the Second World War, yet he managed to get a good education. His intense interest in mathematics started at the age of 12. In 1943, Cambridge University awarded his excellence in this subject by accepting him.

When the war ended, discharged servicemen flooded the university and Pople sought industrial employment for a while. In a couple of years, however, he was able to resume his education at Cambridge. He took many courses, especially in theoretical subjects, and felt an attraction to scientific research. However, he also felt that challenging the likes of Einstein and Dirac would be over ambitious and opted for less crowded fields. At one point he became a research student of John Lennard-Jones, who taught theoretical chemistry at Cambridge, lectured about molecular orbital theory, and was interested in electronic structures. This was a decisive influence in Pople’s career.

John Pople became a research fellow at Trinity College of Cambridge University in 1951, and lecturer on the mathematical faculty in 1954. However, by 1958, he became dissatisfied with his position in Cambridge and wanted to find a new job with more scientific activity. The first attempt was not very successful in that the position he took in a national physics laboratory was burdened by administrative duties. The breakthrough was the result of a sabbatical leave at Carnegie Institute of Technology in Pittsburgh, from 1961 to 1962. This led the Pople family to relocate to Pittsburgh in 1964. He joined the Mellon Institute, which had excellent computational facilities. The Mellon Institute and the Carnegie Institute merged in 1967.

The Poples moved from Pittsburgh to Evanston in 1981 to be closer to their daughter, but he remained affiliated with Carnegie-Mellon. In 1993, his relocation became complete as he joined Northwestern University where he worked, until his recent death, at the Chemistry Department as Board of Trustees professor.
Pople received many awards and other distinctions in addition to the Nobel Prize. He became Fellow of the Royal Society (London) in 1961 and he was knighted in 2003. So, during his last months he lived as Sir John Pople. In 2002, the Royal Society bestowed upon him its most prestigious award, the Copley Medal. He also won the von Humboldt Award in Germany and the Wolf Prize in Israel.

Pariser, Parr, and Pople (L to R) in Chapel Hill, North Carolina, in November 1998 at the occasion of a symposium on Quantum Chemistry in honor of Robert G. (Bob) Parr.”
—compliments of Rudy Pariser

Pople defined computational chemistry as the implementation of existing theory to studying chemical problems by means of computer programs. He preferred not to draw a distinction between computational chemistry and the underlying theory. The theory preexisted, and the computers just enabled it to be implemented much more broadly than was possible before. His approach was to apply theory to the whole of chemistry. His practical approach made him sensitive to considering the “experimental errors” in computational work, something that many computational chemists ignore.

The way he liked to do this was to set up a theoretical model and apply it to all molecules. By applying one approximation to all molecules, he obtained an entire chemistry corresponding to that approximation. This was not real chemistry, but approached it well if the model was good. He used the model to calculate a large number of facts that had also been obtained experimentally. Then he applied statistics and could state that this theory reproduced the experimental facts with certain accuracy. This approach built some level of confidence into that particular level of theory. Therefore, the theory could be applied to a situation where experiment might have not yet existed.

Pople viewed the relationship between experimental and computational work as complementary. He thought that even experimentalists should augment their work with calculations, but he noted that the older generation of chemists was suspicious of theory. He did not think that computational chemistry should be a separate discipline and he advocated for it to be in the general curriculum. He thought that the computer program should be considered a black box, just like a complicated spectrometer, and chemists should learn how to use these programs, and to use them in a critical manner, to understand the limitations of what they find, just like any other technique.

Pople was always more interested in making the computational approach available for application to a large number of people than in going for the highest level of sophistication for some selected systems. He formulated his research strategy back in 1952, when he was still a postdoctoral fellow in Cambridge. This strategy was that one level of theory implies an entire chemistry. He charted this strategy at a time when nothing was yet possible in terms of computational facilities; so he had tremendous foresight. The first theory in this category was the so-called PPP theory, Pariser-Parr-Pople. It handled essentially only one electron per atom and was used for the ∏-electrons of aromatic hydrocarbons. It became very popular and successful in the 1950s. It was a simplified theory, which was possible to apply even without computers in those days.

Pople’s general objective, however, was always to produce theories and the associated computational techniques that would be extensively applicable and illuminate as many chemical properties as possible. This has proved to be enormously successful and was greatly helped by the huge advances in electronic computation. Pople anticipated this technical progress, although not its extent and speed. It might seem that computational technology has advanced so far that there are no longer any limits to computational chemistry, but this was not how Pople viewed advancement. He considered his objectives as such that it will always be necessary to push for more progress.

When Pople was awarded the Nobel Prize, there was universal satisfaction among chemists although he was not a chemist by training. Everybody thought that the 1998 chemistry prize corresponded to the letter as well as to the spirit of Alfred Nobel’s will, which stated that in terms of the prize money, “one part [should go] to the person who shall have made the most important chemical discovery or improvement.” Even if there had been a Nobel prize for mathematics, Pople should have earned the chemistry prize. It does happen from time to time that physicists or even biologists earn chemistry prizes, but it is rare that mathematicians receive them.

John Pople will have a long-lasting impact on how modern chemistry is conducted and where it goes.

In this article, we used extensively materials from the interview John Pople gave one of us in 1995 [I. Hargittai, Candid Science: Conversations with Famous Chemists, Imperial College Press, London, 2000, pp. 178–189].

Dr. Balazs Hargittai is at St. Francis University in Loretto, Pennsylvania, and Dr. István Hargittai is at the Budapest University of Technology and Economics.

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