In the Born–Oppenheimer approximation, the nuclei of a molecule are
assumed to be stationary when the electronic states are studied.
The Schrödinger equation for the hydrogen molecule ion, H+ 2 , can be
solved in the Born–Oppenheimer approximation without additional
approximations. The solutions are molecular orbitals that represent
motion of the electron around both nuclei.
Molecular orbitals can be represented approximately as linear
combinations of atomic orbitals (LCAOMOs).
The electronic wave functions of homonuclear diatomic molecules can
be approximated as products of LCAOMOs.
The valence-bond method is an alternative to the molecular orbital
method.
Molecular orbitals of heteronuclear diatomic molecules correspond to
unequal sharing of electrons.
