An introduction to density functional theory in chemistry

Abstract

This chapter introduces to density functional theory in chemistry. The chapter focuses on the study of stationary molecular systems for which relativistic effects are chemically insignificant; therefore, the use of the nonrelativistic time-independent Schrödinger equation is done. The molecular systems are considered to have a wave function adiabatically partitioned into electronic and nuclear portions; therefore the electronic part can be treated separately from the nuclear one. This is known as the Born-Oppenheimer approximation. Despite these three simplifications, the electronic time-independent nonrelativistic Schrödinger equation is still, in almost all cases, unsolvable. The chapter concentrates on how density functional theory (DFT) can help to solve the Schrödinger equation through an exact procedure that bypasses the calculation of the wave function. Although many density functional methods are ab initio, for historical reasons the latter term are reserved for those methods that are based on the wave function approach to the energy eigenvalue of the Schrödinger equation, as opposed to density functional (DF) methods that use the electronic density to obtain the energy eigenvalue. At the risk of making the already confusing nomenclature even more so, it is important to distinguish between semiempirical and ab initio DF procedures, which differ in whether the functionals have or have not been fitted to experimental data. © 1995, Elsevier B.V.