Chemistry computations earn Nobel prize.

Computers have revolutionized many scientific disciplines, and the field of chemistry is no exception. In recognition of that fact, the 1998 Nobel Prize in Chemistry was awarded to two scientists for their development of computational methods that describe the properties of molecules. Walter Kohn, a physicist at the University of California, Santa Barbara, and John A. Pople, a chemist at Northwestern University in Evanston, Ill., share the honor.

Based on quantum mechanics, the pair's techniques allow chemists to understand the shapes of molecules, how molecules interact, and the results of chemical-identification techniques. Kohn's work and Pople's are "two faces of the [same] coin," says Christopher J. Cramer, a computational chemist at the University of Minnesota in Minneapolis. Both scientists' approaches "have reached very sophisticated levels. This is just the right time for the Nobel prize" for computational chemistry, he says.

In the mid-1960s, Kohn greatly simplified the calculations needed to describe the quantum mechanics of molecules. Previous techniques required scientists to account for the motions of individual electrons, making it nearly impossible to analyze large molecules.

Kohn proved mathematically that it's enough to know the average number of electrons at any one point--the electron density. "His real contribution was in seeing a very different twist to quantum mechanics," says Cramer.

It took about 25 years, however, for scientists to learn how to apply Kohn's method to practical problems. Now known as density-functional theory, it's one of the main theoretical tools of chemists.

Also in the 1960s, Pople developed his novel approach to analyzing the electronic structure of molecules, which he called theoretical model chemistry. He constructed a computational method, applied it to a variety of calculations, and, over time, corrected its weak points.

In 1970, Pople packaged the modeling tools he had developed into a computer program called Gaussian, which he distributed free for many years. In 1992, he incorporated Kohn's density-functional theory into the program, allowing chemists easy access to both techniques, Continually updated, today's commercial version, sold by Gaussian Inc. in Pittsburgh, is one of the most popular quantum chemistry programs available.

Pople was "almost always about 5 years ahead of everyone else in seeing what was possible with digital computing," says Cramer. "The vision he had was just spectacular."

Pople's program gave computational tools to chemists who might not have benefited from them otherwise. Gaussian is "so user-friendly," says Cramer, that "lots of experimental chemists--people who are not theorists-,are able to apply these theories and interpret them."

Awarding this year's prize to both Kohn and Pople makes sense, says George W. Flynn of Columbia University. "It represents a good example of how, in [the study of] condensed matter, physics and chemistry are tightly coupled."