While today, chemical modeling is carried out in computers, in the early 1970s that was far more difficult. Chemical reactions occur at lightning speed. In a fraction of a millisecond, electrons jump from one atomic nucleus to the other. Classical chemistry has a hard time keeping up; it is virtually impossible to experimentally map every little step in a chemical process using physical models.
The researchers laid the foundation for the programs that are now used to understand and predict chemical processes. Computer models mirroring real life have become crucial for most advances made in chemistry today.
Karplus, Levitt and Warshel managed to make Newton’s classical physics work side-by-side with the fundamentally different quantum physics. Previously, chemists had to choose to use either or. The strength of classical physics was that calculations were simple and could be used to model really large molecules. Its weakness, it offered no way to simulate chemical reactions. For that purpose, chemists instead had to use quantum physics. But such calculations required enormous computing power and could therefore only be carried out for small molecules.
In simulations of how a drug couples to its target protein in the body, for example, the computer performs quantum theoretical calculations on those atoms in the target protein that interact with the drug. The rest of the large protein is simulated using less demanding classical physics.
Karplus is currently at Université de Strasbourg, Levitt is at Stanford and Warshel is at USC.