The important aspect of this approach is that it is now possible to arrive at an approximate one-electron
wave function that can be used in other calculations. For example, Slater-type orbitals form the basis
of many of the high-level molecular orbital calculations using self-consistent fi eld theory and other
approaches. However, in most cases, the Slater-type orbitals are not used directly. Quantum mechanical
calculations on molecules involve the evaluation of a large number of integrals, and exponential integrals
of the STO type are much less effi cient in calculations. In practice, the STO functions are represented as a
series of functions known as Gaussian functions, which are of the form a exp( br
2 ). The set of functions
to be used, known as the basis set , is then constructed as a series of Gaussian functions representing each
STO. When a three-term Gaussian is used, the orbitals are known as a STO-3G basis set. The result of
this transformation is that the computations are completed much more quickly because Gaussian inte-
grals are much easier to compute. For a more complete discussion of this advanced topic, see the book
Quantum Chemistry by J. P. Lowe, listed in the references at the end of this chapter.