The application of computation to the solution of problems in chemistry. This include finding solutions to the Schrodinger wave equation, which determines stable configurations of atomic particles and therefore what molecules are physically realizable. Another instance would be modeling the motions of molecules as a result of the various forces acting upon them: electrostatic attraction and repulsion, van der Waals attraction, thermal vibration, etc.
The equations used to determine the stability of a proposed molecular structure analyse the interactive forces between every atom in the molecule. Thus, as the number of atoms in the molecule increase, the number of equations that must be performed go up exponentially. With so many calculations to be performed, the realistic use of this approach to chemistry requires vast amounts of computing power, and super computers and distributed computing are used.
This approach is one of the fastest growing areas of chemistry in the pharmaceutical industry. Instead of having to synthesise and test thousands of possible new drugs in the laboratory, the first stage of elimination can be performed on a computer. This has the twin advantages of saving a lot of money, and reducing the need for dependence on animal testing to understand the chemical interactions in biological systems. In the future it may be possible to eliminate animal testing using this knowledge.