Biomedical Engineering Reference
In-Depth Information
GaussView is
the
GUI for Gaussian 03. The latest version is GaussView 4, and the
MS/Windows version is GaussViewW. It allows you to build molecules, submit jobs and
visualize output. The screenshot shown in Figure 17.1 will give the flavour.
Figure 17.1
A GaussView session
GaussView sits on top of Gaussian 03; use it or not as you wish. It certainly adds to our
quality of life.
17.2 Visualization
Visualization follows the path discussed in Chapter 15, but naturally there are very many
more HF-LCAOs than in the case of dihydrogen. In any case, the HF-LCAOs are not
uniquely determined by the HF procedure. This is because the electronic wavefunction has
to be written as a Slater determinant; one of the properties of determinants is that we can add
together multiples of rows and/or columns without changing their value. This is equivalent
to mixing the HF-LCAOs, and at one time it was fashionable to use this idea in order to
produce
localized
orbitals. Organic chemists place great emphasis on the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). I have
used GaussViewW to produce the HOMO and the LUMO orbital plots for l-phenylanine
in Figures 17.2 and 17.3.
The HOMO comprises large contributions from the benzene ring. By contrast, the LUMO
has a nodal plane through the benzene ring as shown, and a much larger contribution from
the remainder of the molecule.
Plotting individual orbitals is all good fun, but there can be very many of them.
