Sir John Pople, who won the Nobel prize for his work in quantum chemistry, has died aged 78.
Sir John was knighted in 2002
The British scientist won the award in 1998, after joining the Northwestern University in the US two years earlier.
He died on Monday at the Chicago home of his daughter, Hilary Pople. He had been suffering from liver cancer, his family said.
Sir John won recognition for his work on a computer tool that estimates how molecules behave in chemical reactions.
The resulting computer program is used by universities and companies worldwide.
His approach allowed scientists to create computer models of chemical reactions that are difficult or impossible to recreate in the laboratory.
Medics have also benefited from his work - his computer tool is used to simulate the effects of proposed drugs to fight HIV infection.
John Pople was born in 1925 in Burnham-on-Sea, Somerset.
He earned a doctorate in mathematics from Cambridge in 1951.
By 1952, he had formulated his basic plan to make mathematical models for studying molecules without performing experiments.
He was head of the Basic Physics Division at the UK's National Physical Laboratory near London but moved to the United States in 1958.
In 1964, he became professor of chemical physics at Carnegie Tech, which later become Carnegie-Mellon University.
Sir John was knighted by the Queen last year for services to chemistry.
His wife, Joy Bowers, died two years ago. He is survived by three sons and a daughter, 11 grandchildren, and a great-grandchild.