

In regards to your question about a less expensive method to 
calculate molecular energies, you might care to check out
our recent paper:  J. Phys. Chem.  v100, p10083.

Here we calculated the energy differences (electron affinites) between
a number of quinones and their respective radical anions.  We compare
several methods and find that the best is B3LYP hybrid HF/DF method
with a 6-311G(dp) or 6-311G(3dp) basis set.  We found that the G2
method, which you mention specifically, gives very bad results
for parabenzoquinone.

I would very much like to hear about you work as it
progresses.

Sincerely

Anthony K. Grafton
Department of Chemistry and Biochemistry
University of Oklahoma
Norman, OK