Quantum chemistry is a sub-discipline of chemistry focusing on the properties and behavior of subatomic particles, especially electrons, through the application of quantum mechanical principles and equations. Chemical bonds are quantum mechanical; therefore, to understand many of the functionally important properties of molecules requires quantum theory.
Quantum chemistry ranges from the development of the fundamental understanding of molecules, through chemical applications, to numerous applications of quantum phenomena used to study biomedical problems. Examples include the understanding of bond-making and bond-breaking in chemical reactions and the use of coherent quantum superposition states for ultrasensitive measurements of protein and DNA structure and their interactions with drug molecules.
Quantum chemistry is a powerful tool for studying the properties of molecules and their reactions. The development in quantum chemistry methods, especially that of density functional theory (DFT) methods, has made it possible for quantum chemistry calculations to achieve accuracies comparable to those obtained in experiments for molecules of moderate sizes. Also, the rapid development of computer technologies facilitates the use of quantum chemistry to understand, model, and predict molecular properties and their reactions, properties of nanometer materials, and reactions and processes taking place in biological systems.
DFT is a type of electronic structure calculation that has become the dominant method for the quantum mechanical simulation of periodic systems. It has also been adopted by quantum chemists and is widely used for the simulation of energy surfaces in molecules.