Applications of quantum mechanics in theoretical chemistry

Abstract

Progress in the application of quantum mechanics to study the electronic structure of molecules has, until recently, been disappointing and slow. Many difficulties, both of mathematical method and of numerical analysis, arise when there is a large number of particles in the quantum mechanical system. In this review the different ways of applying quantum mechanics to chemical problems are discussed. The accuracy expected and attained by each method is illustrated, but applications to individual molecules are not reviewed.The coming of electronic computers has already produced great changes in this subject. In particular, it is now possible to calculate highly accurate wave functions from first principles for a range of molecules. Direct calculations of this kind are not possible for large molecules and, for these, the problem has been to find suitable parameters which remain constant for a series of molecules and can be used to describe their properties. This problem is intimately connected with the problem of interpreting quantum mechanical calculations in a chemically significant way. Quantum mechanics can also be applied to molecules by setting up models which simplify the quantum mechanical equations but retain those features which are most significant for a series of related molecules.Finally, some of the objectives of current research are briefly reviewed. The wider significance of the subject and its importance for chemistry and the theories of the solid state and the nucleus are also discussed.