Bulletin Autumn‧Winter 1999

Doing Chemistry with Computers ANewApproachIndependentExperiments While c h e m i s t ry is an experimental science, theory (or calculation) is now playing a role of increasing importance with the use of the computer and the development of new calculation methods. The key to theoretical chemistry is molecular quantum mechanics, which deals with the transference or transformation of energy on a molecular scale. Soon after the formulation of quantum mechanics in the 1920s, it was recognized that, in principle, the application of quantum mechanical principles could lead to accurate predictions of many chemical phenomena. This approach of studying chemistry is called ab i n i t i o — L a t i n for 'from the beginning', an approach independent of any experiment other than for the determination of fundamental constants such as the mass and charge of an electron. Yet although the quantum mechanical principles for understanding the electronic structure of matter had been recognized, the mathematics involved in the application of these principles was intractable at best in the 5 0 years that followed. But with the steady development of new theoretical and computational methods, as well as the availability of bigger and faster computers wit h reasonable price tags in the last 20 years or so, calculations have sometimes become more accurate than experiments, or at least accurate enough to be useful to experimentalists. Calculations are also less costly, less time-consumig, and easier to control. And computational results often serve as a guide to experimental chemists attempting to synthesize or discover new molecules. An indication that calculations in chemistry have been receiving increasing attention in the science community was provided by the award of the 1 998 Nobel prize in chemistry to Profs. J.A. Pople and W. Kohn for their contributions to quantum chemistry.