Quantum Computational Chemistry

One of the most promising applications of quantum computing for near-term applications is the calculation of the structures and energies of molecules. Why is this important? One of the fundamental principles of chemistry is the link between form and function. For example, how well a drug molecule interacts with a target virus depends on the form (shape) of the molecule and how well it connects to the part of the virus the drug is designed to attack. Catalysts are another good example, where the shape of the catalyst materials determines the effectiveness of their ability to promote other chemical reactions. More generally, the properties of most complex materials depend on the shape of the molecules that make up the material.

The other key principle is that the different shapes are associated with different energies and it takes energy input or output for the molecule to change from one shape to another. Here is a specific example: When your eye “detects” light, a photon is absorbed by a rhodopsin molecule in the retina of your eye. The absorption of the photon’s energy changes the rhodopsin from a more-or-less straight-line shape (called cis) to a bent form (called trans). That change in shape leads to an electrical signal sent over your optic nerve from the retina to the brain, telling the brain that light has been detected. Knowing the energies associated with those two rhodopsin shapes is important in predicting the efficiency of light detection.