Chemists used to create models of molecules using plastic balls and sticks. Today, the modeling is carried out in computers. In the 1970s, today’s Nobel Laureates laid the foundation for the powerful programs that are used to understand and predict chemical processes. Computer models mirroring real life have become crucial for most advances made in chemistry today.
The work of Karplus, Levitt and Washel is ground-breaking in that they 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.
This year’s Nobel Laureates in chemistry took the best from both worlds and devised methods that use both classical and quantum physics. For instance, in simulations of how a drug couples to its target protein in the body, 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.
The importance of the work of the laureates is independent of what strategy is used for the choice of studied configuration(s). The prize focuses on how to evaluate the variation in the energy of the real system in a accurate and efficient way for systems where relatively large geometry changes or changes in electronic configuration in a smaller part of the studied system is strongly coupled to a surrounding that is only weakly perturbed.
The work behind this year’s Nobel Prize has been the starting point for both further theoretical developments of more accurate models and applied studies. The methodology has been used to study not only complex processes in organic chemistry and biochemistry, but also for heterogeneous catalysis and theoretical calculation of the spectrum of molecules dissolved in a liquid. But most importantly, it has opened up a fruitful cooperation between theory and experiment that has made many otherwise unsolvable problems solvable.