Theoretical chemistry is the study of chemical phenomena with the help of mathematical models and computer calculations. It is different from bench chemistry done in laboratories in that theoretical chemistry is done outside of the laboratory, and is done using supercomputers.

Most of theoretical chemistry is based on quantum mechanics. In fact, another name for theoretical chemistry is quantum chemistry. Theoretical chemists devise mathematical models to determine the properties of atoms and molecules, and to determine how atoms and molecules react with each other. These models are centered largely on quantum mechanical principles. Chemists perform numerically intense computations in order to make predictions from these models.

Though theoretical chemistry can be called chemistry out of the laboratory, there is a strong relationship between bench chemistry and theoretical chemistry. Theoretical chemistry allows chemists to study molecules that have not yet been isolated in a laboratory and molecules...