#### Mathematician who applied his brilliance to quantum chemistry

Sir John Pople, who has died aged 78, was a mathematician who became a pioneer in the field of quantum chemistry. When he shared the 1988 Nobel prize for chemistry with Walter Kohn, the citation read: "We celebrate the fact that mathematics has invaded chemistry; that, by means of theoretical calculations, we can predict a large variety of chemical phenomena."

From different lines of research, the two scientists provided chemists with methods to calculate the bonding of atoms in molecules. Pople was rewarded specifically for developing a computer program called Gaussian, which made possible the theoretical study of molecules, their properties and how they linked together in chemical reactions.

His methods are used today by thousands of scientists in universities and industry around the world to study a vast range of problems in chemistry and biochemistry. With the aid of computer simulations, chemists can now predict how chemical substances will react with each other, in a way that is comparable to the methods used to solve elaborate mathematical equations to make weather forecasts, and calculate the structural integrity of bridges and the aerodynamic characteristics of aeroplanes.

The science of applying quantum mechanics to chemistry began with the basic fact that an atom consists of a nucleus and electrons. The laws of quantum mechanics described the motion of the electrons more than 70 years ago. Scientists realised that those mathematical descriptions contained the explanation of the chemical bond, and, if the equations could be solved, the answer would explain how atoms were bound together to form molecules.

Thus, it should be possible to explain why molecules looked as they did, what their properties were, and how they reacted with each other to form new molecules. In principle, a theoretical description of all of chemistry was within reach. Pople was one of the scientists who recognised the potential that computers provided. Born to ambitious parents in Burnham-on-Sea, Somerset, Pople was told at an early age that he was expected to do more than take over his father's small clothing shop. He went to Bristol grammar school, and recalled developing an intense interest in mathematics at the age of 12; on an introduction to algebra, he was fascinated by simultaneous equations, and read ahead of the class to the end of the book. Coached by two teachers, who he said "were outstanding", he won a maths scholarship to Trinity College, Cambridge, in 1943.

Like other gifted students - particularly in maths, science and medicine - he was allowed to complete his studies, with a view to going on to join military research projects, such as radar, nuclear weapons or code-breaking. But he completed his degree in May 1945 as the war in Europe came to an end, and had to leave Cambridge because the universities were under pressure to find places for a flood of ex-servicemen.

Pople took a job with the Bristol Aeroplane Company, but was determined to use his mathematical skills in some branch of science, and kept looking for a way to return to Cambridge. It came in 1947.

He promptly took as many courses as he could squeeze in, including quantum mechanics, fluid dynamics, cosmology and statistical mechanics. He was lucky enough to become a research student with the distinguished theoretical chemist John Lennard-Jones, even though he had almost no chemical background.

Pople's next 10 years were spent as a research fellow at Trinity College, and then as a lecturer in the mathematics faculty. He recalled that his general plan of developing mathematical models for simulating a whole chemistry was formulated, at least in principle, some time late in 1952.

At that time, computational resources were limited largely to hand calculators. At the end of 1955, Pople developed an interest in nuclear magnetic resonance (NMR), which was emerging as a powerful technique for studying molecular structure. He spent the summers of 1956 and 1957 at the national research council in Ottawa, Canada, working on the theoretical background of NMR.

By 1958, he had clearly changed from being a mathematician to a practising scientist, and had become dissatisfied with his position at Cambridge. He became head of the new basics physics division at the National Physical Laboratory, near London, but it involved too much administration for his liking.

A sabbatical year in the United States convinced Pople that the environment for theoretical chemistry was better in America, and he accepted a post as professor of chemical physics at Carnegie Institute of Technology, in Pittsburgh. There, he returned to some of the fundamental problems of electronic structure that he had thought about at Cambridge, aided now by powerful computers that could develop computer models of chemistry. He was made a fellow of the Royal Society in 1961, and knighted in 2003.

His wife Joy, whom he married in 1952, died two years ago. They had three sons and a daughter. ·

John Anthony Pople, scientist, born October 32 1925; died March 15 2004

Pearce Wright

19 Mar 2004 © Guardian Newspapers Limited 2004