A one-electron wavefunction describing an electron moving in the
effective field provided by the nuclei and all other electrons of a
molecular entity of more than one atom. Such
molecular orbitals can be transformed in prescribed ways into
component functions to give '
localized molecular orbitals'. Molecular
orbitals can also be described, in terms of the number of nuclei (or
'
centres') encompassed, as two-centre, multi-centre, etc. molecular
orbitals, and are often expressed as a linear combination of
atomic orbitals.
An orbital is
usually depicted by sketching contours on which the wavefunction
has a constant value (contour map) or by indicating schematically the
envelope of the region of space in which there is an arbitrarily
fixed high (say 96%)
probability of finding the electron occupying
the orbital, giving also the algebraic sign (+ or −) of the
wavefunction in each part of that
region.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1142